Guide to Water-Resistant Design and Construction Techniques: Changes vs. Time

SOME HISTORY

Ever since humans began to evolve, we have been struggling to do more than survive. We want to protect our families from predators, feed and clothe them, and protect them from a sometimes hostile environment. Global warming isn't anything new; researchers tell us that we've been having cycles of hot and cold every hundred thousand years or so. The hot cycles lasted about 20,000 years, followed by another 80,000 years of ice. Our human ancestors learned to adapt to their changing environment.

Early shelters were constructed mainly out of native materials such as cut earth, stone, wood, and animal hides. African fossils have led many historians to the conclusion that the Olduvai Gorge area of Africa must have been the home for the earliest hominid habitat, around two million years ago. We find evidence of changing climate, both temperature and humidity. It had a tropical climate and lush vegetation between 1.2 million and 700,000 years ago, which then changed to a dryer, arid climate. In northern China , prehistoric people used naturally occurring caves and caverns to survive the cold winters as early as 800,000 B.C. In Europe , basalt and granite walls were used as wind breaks as far back as 970,000 B.C. Our ancestors may have seen and used fire earlier, but it seems they learned to control fire about 500,000 years ago. Could you imagine the sense of security that fire must have brought to them back then? Not only did it offer warmth and light their caves, but it also offered protection against many predators. Nomadic hunter-gatherers are believed to have built the first artificial shelters nearly 180,000 years ago around the same time they learned to use tools. Humans soon learned to plant food and raise domesticated animals. This changed everything. Soon, civilizations began to form in support of common goals.

Early shelters.

The last ice age ended about 35,000 years ago. Since then, the explosion of knowledge and development of specialized tools has led to rapidly advancing cultures across the globe. We have seen tremendous advances in travel, medicine, arts, and sciences. As people satisfied the more basic needs of food and shelter, they began to seek out ways to satisfy higher-level needs, such as knowledge and wealth. In some cultures, this led to war; in others, a search for meaning.

Each culture since that time has been developing an identity of its own in response to climate and social differences. In Asia , civilization was deeply influenced by the ruling class. Different dynasties and conquering invaders tended to shape the built environment. In coastal Chinese areas, average annual rainfall exceeds 80 inches (2 meters) per year. Steeply pitched roof forms and wide overhangs were used to combat the natural forces. Central columns were used to support the roof systems. Buildings became highly ornamental in the Ming and Han dynasties. As intercultural trade expanded, so did the forms of building expression. The Chinese developed a process of apprenticeships for developing construction skills through generations of workers. In Europe , the dominant forms were mostly constructed of masonry, as brought by Greek and Roman conquerors. Stone and wood were used to span between closely spaced stone columns. The Romans forced their skilled masons to travel as part of their army, engineering solutions and building masonry buildings wherever they extended their empire in Europe , Africa , and Asia .

CHANGES vs. TIME

In North America , native settlers were quite nomadic until the Europeans over whelmed them some 500 to 700 years ago. These Spanish, English, and French conquerors brought their customs and building forms with them as well.

Following the Industrial Revolution, mass transportation and electricity began to change the world at an entirely new pace. With the invention of locomotives and automobiles, there was no limit to where we could go and how we could get there. It was more a question of how fast we could get there and what we would do when we got there.

Starting about 1950, people were now able to live in areas where conditions were previously difficult to bear. We really began to dominate our environment in true European fashion. With the end of World War II and a recovering economy, Americans began moving to the hot, humid areas of the South at a record pace. Rich and poor alike were on the move. Many of those migrating built only modest structures in their new locations, limited by their means and uncertain futures. Lower cost homes commonly were shotgun-style one-story structures, considered perhaps temporary or short-term solutions in case the family didn't like them, or they couldn't stand the bugs. Some people, however, brought their comfortable forms with them from the colder climates, building a Cape Cod-style home out of lap siding in coastal Florida . Well, coastal Florida has a different climate than Cape Cod . In the summertime, such structures needed more roof overhang, and in the winter, they benefited from more thermal mass and insulation.

Recognizing a need to protect the public health and welfare, people began to establish building codes. Engineers, builders, insurers, designers, and businesspeople all worked together to form associations and draft regulations.

Since establishment of the codes and regulations, permitting agencies have continued to introduce more rules for building envelope performance. Many jurisdictions adopted energy codes as a means for requiring more efficient consumption and to encourage conservation of energy.

RECENT TRENDS

Shade and natural ventilation.

Simple wall section, plan view.

PT or Cypress Sole Plate 2 by 4 Wood Studs Lap or Bevel Siding Whitewash or Similar Coating Diagrm. 4 Simple wall section, elevation view.

Lath and Plaster Wood Siding Sole Plate Wood Starter Joist Girder Floor Joists Foundation Posts Stud Framing Many of the early buildings in the United States were constructed of native materials. Pine and cypress were the most common wall materials used. Some cities where clay was mined locally made bricks. Most building occupants relied on natural ventilation and shade for human comfort (see Diagrm. 2).

After the Industrial Revolution, more and more building materials were widely distributed. Concrete block became as common for walls as frame construction.

Since the 1960s, most of our commercial buildings have been designed to be air-conditioned. Even residential buildings typically operate with all the doors and windows closed. Occupants have become more reliant on air conditioning systems to introduce outside air for breathing and comfort. The building envelope has become much more complicated during the same period of time. Where we used to nail cypress siding right to exterior wood stud framing, we now use layers of sheathing, vapor retarders, insulation, and a variety of finish materials (see Diagrm. 5). As a result of these and other factors, buildings have become more difficult to design and construct.

With improvements in living conditions, more and more people are moving to coastal regions. They have begun to spend more of their time inside buildings than previous generations. With this has come the increasing challenge of keeping the indoor environment healthy. With increased energy costs, we find our buildings becoming "tighter." By this we mean that we have less air moving through the building envelope. This also means that it's more difficult for water that may get into the building to drain out (see Diagrm. 6).

Diagrm. 5 Complex wall section. [Interior Paint Interior Sheathing Concrete Masonry Units Metal Framing with Insulation Waterproof Membrane Air Infiltration Barrier on Sheathing Stucco on Lath Exterior Paint Furring] Another result of the increased population is the drastic need for housing. Homes are being built faster and selling for higher prices than ever before. Many buildings that were built as hotels or apartments have been sold as condominium units. The result of all these factors is that we have seen an increase in the number of claims against developers, builders, and designers. What can be done? The answer is both simple and clear. We need to design and build better places.

Designers must do a better job of developing plans and specifications that lead to good solutions. Builders must make good decisions and do a better job of quality control during construction. Developers must enable design and construction teams to come up with long-term, successful solutions. We can't let poor management decisions lead to lawsuits. As a team, we must resist the urge to save a few bucks if it can result in problems in the future. This is not to say that just by spending more money we can prevent problems either. What is the right answer? How can we design and build better places? Diagrm. 6 Water becomes harder to drain out.

Diagrm. 7 Increase in number of claims.

We need to learn from problems of the past. We can look at cause-and-effect relationships. Then we can pay attention to details. We can provide excellent construction details and help to make sure that they get installed right. It takes a cooperative team effort from the office to the field-and back. Lessons learned in the field need to be communicated back to the designers and programmers and should be used to educate owners.

Feedback loop.

COMMON CAUSES and EFFECTS

This section looks at problems that have been identified from the past. It looks at the contributing factors causing problems and explores ways such problems could have been avoided. In Sections 3 through 6 you will find more detailed information for application through design and construction.

This includes typical roof, wall, and floor details for different building types.

These details are discussed in relation to the most basic geometric aspects.

Materials are called out, and fasteners are shown, as well as flashings and sealants. Our objective is to provide a methodology for preventing the most common problems identified as contributing to building envelope failures and potentially to mold growth. Following is a list that includes 25 of the most common problems:

1. Materials got wet during construction.

2. Dew point is reached in a wall without planning for condensation removal.

3. Insulation is inadequate, misplaced, or on the wrong side of the vapor barrier.

4. Leaks at windows and doors or at other holes in the walls.

5. Roof penetrations.

6. Water comes in at the intersections between walls and floors.

7. Inadequate ventilation.

8. Negative-pressure building.

9. Inadequate air-conditioning.

10. Bad laps of membrane.

11. No vapor barrier.

12. Expansion of materials over time.

13. Bad design.

14. Poor construction.

15. Membranes damaged during construction.

16. Poor joint geometry.

17. Building below finish grade.

18. Hydrostatic pressure.

19. Poor maintenance.

20. Reliance on sealants.

21. Wrong material for the job.

22. Exposure to ultraviolet (UV) radiation during construction.

23. Failed roofing products.

24. Reliance on coatings instead of membranes.

25. A series of bad decisions and /or other forces.

Moldy sheathing.

Materials got wet during construction

Very few building materials can be rained on during construction without increasing the potential for future problems. Many builders today strive for just-in-time (JIT) delivery for materials in order to minimize the risk of expo sure, theft, damage, etc. With the volatility of the markets and the competition for materials, some materials often get stocked months before they are installed. General contractors struggle to protect stored materials, often renting warehouses for months just to limit their exposure to inflation or shortages.

There are times when a contractor may choose to install drywall or other interior materials before the exterior building envelope is complete. Any organic material such as drywall should not be installed in standing water or where it can be rained on. There are more inert materials such as glass-fiber-reinforced sheathing materials that have no paper backing and that can experience incidental water exposure without requiring removal. Block and brick should be stored so as to stay clean and dry until used. Even the best-stored materials can grow mold if spores are present and temperature and humidity are right to sup port growth. If materials get wet, you must make a decision about their removal. If organic or hygroscopic materials remain wet longer than 12 to 24 hours, they should be removed and replaced..

Dew point is reached in a wall without planning for condensation removal

When humid air cools by a few degrees, condensation can occur.

Condensation is the formation of small water droplets. These drops are formed when air cools to where it can no longer hold water vapor in the gaseous state.

We call this the dew point. Water is needed for mold growth. If we can prevent condensation, we will reduce the potential for mold growth. Careful consideration should be given to modeling the point in the wall section where condensation is likely to occur. Temperature and humidity can be calculated to prevent condensation in normal conditions and to provide drainage pathways for moisture formed in extreme conditions. Condensation can form on a cool surface in a wall, such as metal furring or studs. Good design dictates that each material used in the wall cavity must be selected carefully. Refer to Section 4.4.5 in Section 4 for condensation avoidance. If condensation is allowed to build up, structural damage can result.

Insulation is inadequate, misplaced, or on the wrong side of the vapor barrier

Some designs leave inadequate space for proper insulation. Others may use cold-climate wall sections for hot-climate buildings. This problem can be as simple as insulation being installed on the non-conditioned (warm in the summer) side of the vapor retarder in walls. Some builders use foil-backed fiberglass batt insulation in such a way that the fiberglass stays wet and drips liquid water into the wall cavity, increasing the potential for bacterial growth. If the insulation has too low an R value, interior finishes may warm to where the dew point is reached. Wood paneling, ceramic tile, and drywall can provide environs for mold and other undesirable growth.

If the vapor retarder is placed on the cool (interior in the summer) side of the insulation, the increase in the moisture level of the insulation will reduce its effectiveness. This results in wasted energy and potential moisture problems in the wall. Refer to Section 4.6.8 in Section 4 for more on insulation.

Leaks at windows and doors or at other holes in the walls

This is a wide-ranging issue and includes openings in wall planes. Window and door frames can be difficult to seal properly against leakage. Other problematic penetrations may include such things as louvers, vents, lights, and beams. As designers, we can carefully select the right kind of product to match the materials and methods of construction. We should skillfully create the plan and section view details to both prevent wind-driven moisture from entering the walls and to allow drainage pathways for water that may pass the outermost protective barriers. This must occur at the head, jamb, and sill and continue to below grade.

With the development of better sealants and products such as expanding-foam fillers, builders have become more dependent on them. Whereas we used to rely mostly on positive detailing applied over the flange or water tables at the head, we now have a tendency to leave an intentional gap and use negative detailing. These gaps may vary from 1/4 inch to more than 3 inches. Both foam fillers and sealants (formerly referred to as caulk) have been proven to fail over time.

Roof penetrations

There are many different problems we see related to roof penetrations and construction. One is the result of water continually ponding or left standing on the roof membrane. As a result of continued contact, the membranes begin to break down. Membranes are not meant to stay wet. Most roof failures occur at penetrations or where different systems come together. Failure to seal and flash intersecting roof planes and vertical parapets causes most common problems. The result is damaged substrates, which can lead to mold and mildew problems over time. When a roof membrane is being removed during renovation, remodeling, or reroofing, you can see where water has been repeatedly defeating the membrane. This typically occurs at hard-to-flash areas, such as skylights, chimneys, and vent stacks on sloped roofs.

Another common problem results from difficulties in fully sealing scupper penetrations and internal gutter or leader construction. Metal gutters in commercial buildings also can fail to hold water for a number of reasons. Most integral gutter failures are related to movement over time, but horizontal and vertical laps also can be problematic.

Sealants fail over time.

Integral gutter section. [Top of Parapet Water Level in Gutter Higher than Lap in Metal Water Enters Wall here]; Finish floor above finish grade.

Water comes in at the Intersections between walls and floors

Many one-story buildings use slab-on-grade construction. Multilevel commercial and residential buildings have walkways and balconies. Accessibility codes have made it more challenging to keep positive drainage away from walls.

The point where walls connect to floors is one of the most difficult-to-control moisture infiltration areas. The best protection against infiltration of large quantities of liquid water is to keep the finish floor more than 6 inches above finish grade. There are several proven methods for closing the voids between sill plates and floor slabs, but the best prevention is an elevated slab.

We recommend use of gravity and geometry as a basis for prevention of water intrusion at the base of walls.

During storms, wind-driven rain can impact our walls at more than 100 miles per hour. Sometimes the droplets come in horizontally or even in an upward direction. Good design and construction can provide barriers that prevent water from natural or human-made sources from defeating the building envelope. It starts with good detailing.

These details must provide planned-in pathways for the moisture to drain out.

Some studies in 2003 reported that block walls built on slabs at grade with no insulation, no furring, and no drywall typically have not supported mold growth as much as some of the more complex wall types. It is believed the biggest contributing factor to their resistance is that there is no place to trap water in the wall. After a rain event, the wall can dry out fully.

Multiple wythe walls create an even bigger challenge. Water can get trapped in between the wythes, creating good environments for organic growth. Brick, block, and stone walls built today often have interior components framed into them.

Insulation is often installed between the framing members. Designers must pay special attention to details where multiple layers of wall construction are used.

Inadequate ventilation

Ventilation is important for human comfort, as well as to prevent or minimize bacterial growth. Studies have shown that the best way to avoid bacterial growth in walls is to keep the temperature cool and the air dry. This is difficult to do in warm humid climates or if it's cold and damp out. The difference between indoor and outside air temperatures can cause condensation in the walls. The moisture in walls needs to be removed. It should be aided by ventilation. Attic spaces, wall cavities, and crawl spaces must have adequate ventilation to inhibit bacterial growth and to maintain relatively dry materials to prevent rot. Historically, builders strove to maintain less than 50 % relative humidity (RH) in occupied spaces.

The American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE) is working to develop new guidelines slated for adoption in 2007 that lower design values to new levels (among which is a recommended 40 percent RH in hot humid climates). This should result in two things. First, it will result in larger cooling-coil capacity. Second, it should help to prevent humidity from reaching high levels in the building, even in peak conditions. We should keep air in the wall cavities, especially those inside of vapor barriers, at less than 50 percent RH to minimize the potential for mold growth.

Brick vents in section.

In brick and stone walls, for example, we typically design vents and weeps to minimize trapped water in the cavity. Vents typically are installed under window sills and at the tops of walls under roof overhangs. This enables water vapor in the cavity to migrate out as it rises up. Weeps are important at the low points of these walls. They should be installed by way of tubes, flashings, or water tables to get liquid water (from infiltration or condensation) out of the wall cavity. Ideally, the point of discharge is below finish grade so that any staining caused by the discharge is not visible. Discharge above grade requires additional treatment, such as change of materials, or acceptance of discoloration. Removal of the liquid and vapor water is important to minimize the possibility of contaminating the conditioned spaces. Ventilation is the key to removing water in the walls.

Inadequate ventilation also can take many forms. If conditioned air is not circulating properly, there can be warm dead-air spaces in the rooms. These also can be places for growth on and in the walls. It is also key to remove warm, moist air from occupied, closed spaces within buildings. An example of this would be in showers and laundry areas (see Diagrm. 14). Ventilation is also important for flat roof systems. We like to specify vented deck to promote drying if light- or normal-weight concrete is applied. This removes moisture from curing concrete faster. Then we design vented membrane systems to allow hot air to escape above the concrete.

One challenge with vented metal deck is to limit the problems that can result from dripping and deck draining long after concrete placement.

Plan for moisture removal at sources.

Outside air system diagram.

Heat wheel.

Negative-pressure building It is now a building code requirement in many states to have positive pressure in occupied buildings. What this means is that more air is brought into the building than is exhausted. Diagrm. 15 shows a section through a representative four story building. In it you can see a schematic flow of air to and from the outside air conditioner. It also indicates the other components of a building pressurization study-exhaust, vents, and exfiltration. Exhaust is the sum of all building fan-induced components, such as bathroom, kitchen hood, or bathroom exhaust.

Vents are dryer vents, items such as gas appliances, and plumbing vents. The exfiltration component is for air exiting the building through windows, doors, and perimeter leakage. The sum of all the negative values must be less than the amount of outside air coming in for the building to stay positive.

In most cases, the outside air is ducted to the suction side of the air-conditioning system and mixed with the return air. Some buildings have sophisticated sensors that measure exhaust air and outside-air makeup and , through a series of variable-speed fans, are able to maintain positive building pressure. The sensors work together to control fan speed or dampers to keep more air coming in than goes out. An enthalpy wheel is sometimes used to capture energy from leaving air and transfer it to entering air. Such wheels, often referred to as a "heat wheel", result in lower energy costs as well.

The key component of a well-designed and well-balanced system is the unit air-conditioning system. Diagrm. 17 shows ducted return air and a backdraft damper to the outside air duct. This can prevent unwanted loss of return (pre conditioned) air.

By keeping the building pressure positive, we can minimize relative humidity in our building roof, exterior walls, and their cavities. Negative-pressure buildings can lead to the continual introduction of warm, moist (in some cases dirty) air. This can lead to the slow buildup of hidden mold that can be tolerated at low levels for a long period of time. Sometimes a single trigger event, such as a hurricane, can cause the rapid spread of bacterial growth to intolerable levels within a few days. The hurricane force winds can blow water into the envelope and then afterwards loss of electrical power for days or weeks. If you couple a negative-pressure building with high-humidity conditioned air (such as may be caused by an undersized coil section, high chilled-water temperatures, or too high an air velocity), you have created a moist environment where bacteria can flourish. Once mold reaches this level, remediation is quite costly and requires many affected materials and systems to be removed completely and replaced.

Unit air-conditioning system.

Inadequate air-conditioning

There are many ways the air-conditioning system can contribute to indoor environmental problems. There are just as many reasons why a project can end up with inadequate air-conditioning. On some projects, design decisions or assumptions may be flawed. The design team has to make many decisions.

Maybe some of those decisions may not have been fully communicated to all team members.

Perhaps design insulation values were miscalculated or otherwise not achieved. Perhaps cost-cutting decisions were made that were not consistent with design values. Maybe the system was designed for 95ºF days and fails if temperatures hover around 98ºF . In the Diagrm. we see that temperatures stayed above 95ºF for a long period of time. If the envelope was not sufficiently insulated (and few are), the transfer of heat through the envelope will exceed the unit's ability to reduce temperature and humidity in the conditioned spaces. This will result in the perfect environment for bacterial and fun gal growth. The way around this is to have the design engineers raise the design values. In most cases, about 5_F more in design values will provide enough additional cooling capacity to handle the worst summers. Some systems can keep the air cool enough but fail to dehumidify it adequately. This can result in RH in the space exceeding 65 percent, an undesirable value.

Maybe chilled-water values discussed during planning stages, and supposedly delivered by the local municipal utility company, were never actually provided to the building site. This happens in cities that are experiencing rapid growth.

Cities, counties, hospitals, schools, and large commercial projects often provide the design team with expected values for chilled water to be provided by existing supply loops. As more users are brought into the loop, historical values may not be met. This can result in reduced capacity for cooling and dehumidification in the new building, as well as problems in the older ones in the same loop.

Temperature over time.

There are many operational reasons why the system can prove inadequate.

Perhaps there is insufficient maintenance of the condenser water tubes or poor control of chemical treatment. Both of these can lead to poor heat transfer and less cooling capacity. Sometimes there can be a great system that was installed poorly. Perhaps the ductwork is leaking, crushed, or undersized. Controls failures or bad settings also can lead to poor performance.

The system must be capable of maintaining temperature and humidity control in whatever operating conditions. Most designers will derive guidance from standard practice in the industry. Most owners or developers will not review or participate in the establishment of system design parameters. We often get feedback from owners or contractors about ways to save initial costs on the air-conditioning system. Some projects suffer from poor cost savings measures. There was one project a major firm worked on where the owner was offered a big savings to switch from a central plant and chilled water system to direct exchange (DX; i.e., air to air) units. The designers recommended against the change, but ultimately, it was made. The DX units had undersized coils for the amount of outside air and could not provide enough cool, dry air to the spaces. Problems were observed by fall of the first year. Litigation followed against the designers, who had recommended against the change in unit.

There are other ways the system may not perform as well as needed. The system may be well designed and fully capable of doing the job. Sometimes the problem may be the result of controls settings. After owners and operators take over control of a building, things are likely to change. One of the first things to change is set points. In a large building with a central plant, air and water set points can be changed by anybody with a password. In an attempt to lower heating or cooling energy costs, operators can change set points. If the supply air temperature is set 2ºF warmer, the operator might save a thousand dollars per week in the summer. This is an easy and obvious decision for someone with budget responsibility, especially if he or she has no training in mechanical engineering.

Other tempting changes include closing off the outside air makeup grill, raising the humidity set point, or turning unit resistance heaters off. All these changes are likely to result in an increased potential for mold and mildew growth. The way to avoid these problems is by keeping focus on the big picture-long-term successful operation of the building. Do not permit decisions to be made only to help the short term if they have long-term negative effects. It is up to the decision makers in each project to balance the input with the project needs and come up with a good, well-balanced set of design and construction values to be met. This should be done in the programming phase, not after design documents are near completion. Good project managers will use their experience to adjust the design values pro vided by others so that the design and construction teams end up providing a successful building.

Bad laps of membrane

In walls and roofs that use sheet membranes for vapor or air infiltration barrier, the manner in which the membranes are installed is very important.

Manufacturers provide clear instructions on recommended procedures and will only warrant properly installed products. Sometimes even the simplest tasks can be performed poorly. The most basic aspect of a properly installed sheet membrane for air infiltration is sealing the seams. The joints between successive layers of sheeting must be sealed by the right product. For example, manufacturers may recommend that applications of XYZ Air Infiltration Barrier are sealed at fastener penetrations, ends, and laps with XYZ brand tape to maximize performance of the product.

After you get past the obvious, each penetration through the wall, such as windows or electrical devices, must be sealed in the same manner. Rather than rely on foam or tape, installers should seal penetrations, lapping each successive sheet of material from the bottom up. All laps above grade typically need to be installed from the bottom up, with each successive layer lapping over the one below. Just as with roof sheathings, membranes on wall surfaces should be installed to direct water down and away from the building. Whether air infiltration barriers or water proof membranes, laps should be installed using gravity to prevent the introduction of water.

Diagrm. 19 Avoid backwater laps.

[Backwater Lap Wood Siding WaterProof Membrane Backwater Lap Sole Plate Plywood Flooring Joist Girder Floor Joists Wall, Below ] There are proper ways to seal the tape to the membrane as well. Both surfaces should be dry and free from dirt, grease, or foreign materials. Self-adhesive membranes should follow similar procedures. Fully detailed plans will include graphic and written instructions for proper application of membranes. Specifications should match products with applications. Special care must be taken to match sealants with membrane products if they come in contact with each other.

No vapor barrier

Each climatic condition requires a different treatment with regard to air and vapor retardant. Each client and building system has different requirements.

Many buildings have problems resulting from not having an effective air infiltration or vapor barrier. Many thousands of buildings have been constructed without any vapor barrier at all (see Diagrm. 20). Others rely on stucco on block to prevent water (in liquid or vapor form) from entering the building envelope.

Some use flake board or siding to protect the shell, whereas others rely on a coat of paint to function as air and water protection. Even if this works when new, it relies on proper maintenance, such as additional coats after 5 or at most 10 years. Beyond this, in the flake board or plywood sheathing example we are relying on a system component to do more than it should. If building felts are installed in a wall, can they be an effective air barrier? Perhaps, if the joints are sealed tight with a roofing cement product, but this is not what it's designed for. Some types of sheathing, when joints are sealed with proper materials, such as a fiber reinforced mesh and mastic system can be used as an air infiltration barrier. The biggest issue here is matching the wall type with the climate, especially amounts of rainfall and temperature ranges.

Wall section without vapor barrier.

Expansion of materials over time

Some building envelopes may work well when constructed, only to fail later.

This can be the result of material movement over time. Forces such as deflection resulting from wind, expansion and contraction due to temperature changes, or uneven foundation settling can lead to leaks. In some cases, leaks are caused by cracking of structural and /or finish materials. In others, leaks can be the result of failed sealants at joints. If initial installation of roofing membranes does not provide for adequate movement, resulting forces can rip the materials. All materials tend to expand and contract as they change temperature over the course of a season or even a 24-hour period. Temperatures on a roof coping can vary more than 80ºF in one day. Therefore, long lengths of any envelope component must be designed and constructed to permit movement without loss of protection. In metal, we often rely on elongated fastening slots, such as Whitney slots, to allow for tight fit and expansion, or contraction without compromising the performance of the joint.

Similarly, joint covers are designed to be pinned on one end and slide on the other.

Refer to Section 4 for more on roof flashings.

Slots to permit movement.

Building section where details need to be drawn.

Bad design

It may be that the design documents show a bad detail or neglected to address an important force. In an attempt to create a certain aesthetic, some designers can end up with a bad detail. This could occur at any location in the building but most likely would be at the floor or windows and doors. Another possibility would be at the roof edge, such as drip, parapet, or fascia. --- plan and section locations that must be designed and detailed in even the simplest buildings to control water intrusion.

Poor design can result in water intruding into or forming in a wall cavity or building interior. Good design typically will locate roof planes above door openings to reduce wind-driven rain energy. Some designers feel the need for new expression. They develop new ways to solve timeless problems. A different explanation for a bad detail might be the lack of experience on the part of some member of the design team. For less-experienced designers, using time tested details will reduce the possibility of bad details. Many project teams use waterproofing and roofing consultants to review plans and specifications during the design process. This reduces the likelihood of bad details. Some consultants will develop your details for the project and share in the liability.

There are other ways designs may not illustrate the best solution for construction.

If, for example, we have long spans that may deflect over time or with changing live loads, the right design response might include deflection tracks or expansion joints to accommodate the movement without leaking over time. Another example of bad design could be the location of a chimney flue or mechanical vent in a valley condition. Still another would be failure to slope the exterior grades away from all four sides of the building. These and other flawed design decisions can be caught in peer review before release of drawings, by building contractors, by plans examiners, or by other design professionals during their review. Only by all of us working together as a team can we consistently produce the best product.

A significant portion of this guide (all of Section 4) focuses on design. We felt that this was necessary because so many decisions are made in the design process that affect envelope performance.

Poor construction

Alternatively, the design decisions all could have been sound. The submittals all could have been equivalent to the basis of design. A poorly performing building can be the sole result of poor construction practices. It can be the result of a poor application of materials designed to prevent liquid water intrusion. If the air-conditioning system dries the indoor supply air adequately, water vapor is much less likely to be the cause of bacterial growth or material damage. It is most often the result of condensation or liquid water intrusion.

Even small quantities of liquid water, if frequent, can lead to big problems.

As you can imagine, the roof can be the most frequent location for a source of water intrusion. Low slope or flat roofs, if installed improperly, can trap water where it can find its way into buildings (see Diagrm. 23). If the installers don't install flashings and membranes properly, the building will likely have problems. Frequently, leaks can occur at corners and where horizontal surfaces meet vertical surfaces.

As the materials expand and contract with changes in temperature, rips and tears can occur in the membrane. Laps and seams are less frequently the cause of leaks, yet leaks still can occur there. Proper application and protection would be more important in the use of a single-ply roofing system than with the case of a three-ply membrane system. On sloped roof surfaces, there can be many causes of leaks as well. Commonly, the dry-in membrane is installed months before the metal or shingles go on. Most manufacturers will not war rant performance of their products if they are exposed to UV radiation for more than 30 days. If the membrane is not nailed properly or fully adhered, rips can occur. If it's not stretched properly or installed when the rolls are cold, it can develop big bulges or humps in it when the material warms. Some roofers have been known to cut the membrane with knives to get the bumps out prior to installing the shingles. This practice basically voids the integrity of the membrane.

Water can enter a building when trapped on the roof.

Plumbing vent detail.

Shingles are not intended to serve as the membrane; they are intended to keep the sun off the membrane beneath. Additionally, flashings along sides of sloped roof surfaces need to be installed in such a way as to prevent water intrusion.

Laps in metal or sheet membranes must be made the right way. Penetrations such as vent pipes or equipment supports must be sealed properly and should extend a minimum of about 12 inches above the roof (see Diagrm. 24).

All too often, walls and roofs are penetrated after the air infiltration barrier or waterproof membranes have been applied. Proper installation of penetration protection relies on timely or sequenced installation requiring coordination among many trades. Many of our projects today are built entirely by subcontractors specializing in one trade only. It has become more difficult to manage the sequencing and coordination of trades. The roofer usually installs flashings and membranes at the roof, it's a good idea to have the responsibility for roofing membranes and flashings to reside with one contractor.

A building could have some concrete, some block, and some metal stud (usually including drywall and exterior gyp sheathing) subcontractors. The electrician, plumber, air-conditioning, and miscellaneous metal subcontractors often penetrate the other contractors' completed work. One way to seal the late penetration is to remove finish materials back far enough to access the membrane.

Then slit the membrane above the new penetration and slip a piece in behind the original sheet. Tape it, and fit the new piece around the penetration. Then replace finishes.

In some contractual arrangements, the sealing of the penetrations falls to the person penetrating the other subcontractor's work, whereas in others it goes back to the original installer. Some projects may have a caulking and sealant subcontractor. It gets very challenging to get them all to work together with the time constraints of the other interdependent subcontractors. It only takes one of the many trades not being cooperative to cause problems for all the others.

--- presents an enlarged detail for a portion of the envelope, calling out materials requiring coordination. It also lists some of the many trades that all need to go in the right sequence. Prior planning and two-way communications are the best preventive measures. It used to be that sleeving wall and slab penetrations was the norm. The space between the sleeve and the penetrating pipes or conduits would be filled later. Now, the norm has changed. It is more common to see the penetration core drilled through a floor slab or busted through a wall. In many cases, the membranes are already complete and finishes installed. Any penetration at this late stage can't be sealed properly at the air infiltration barrier level without backing up (as opposed to moving for ward). If the air barrier is not sealed to the penetrating object, the integrity of the building envelope's continuous air barrier is at risk for failure.

Windows and doors are the next likely source of leaks. We have seen many projects where concrete walkways around the exterior walls were constructed at an elevation slightly higher than the finish floor elevation. Let us assume that they were not designed as such, but are the result of inconsistencies in placing concrete at slab-edge forms, thus the walks got placed too high. You can see this condition in Diagrm. 26. This can lead to frequent introduction of water under perimeter walls.

When this occurs at entry doors, water can find its way in easily. The addition of sill pans at doors can help prevent intrusion at doors. At windows (and louvers), flashing is also extremely important. Many installers tend to rely on sealant (often by others) to prevent water from coming in at their penetrations.

Holes are often cut the wrong size, air infiltration barriers (AIBs) are installed before blocking, flashing is omitted, or worse. One contractor tried to fill in the void along a slab edge at grade that resulted from bad layout of the slab and walls with additional pieces of filler material (see photo of the filler and surrounding voids.). This required corrective concrete work (backing up) and properly adhering cementitious filler to the slab edge.

We would like to take this opportunity to discuss an opinion that we formed over the past several years working on large commercial and government projects. Our detailed drawings need to be done to a different level of detail than in past decades. We seem to have a less-skilled workforce available. Many of our workers don't speak or even understand the language in which the plans are provided. For these reasons, our plans, sections, and details need to be more graphic and easily understood than in recent history. It used to be that a section at 1/8 inch per foot scale and some general notes would suffice for defining a wall-to-roof intersection. We can no longer just note "Install as per manufacturers' recommendations."

Photo as detail was constructed.

Now we have to almost provide a recipe for construction. We have to show every part of the system, call each component out, and indicate where it goes.

We can't even expect our workers to understand abbreviations anymore. We have begun providing enlarged details at 3 inches = 1 foot, or even full size.

This is the best way that we have found to guarantee proper estimating and construction. This places a huge burden on our design teams, requiring more time and effort to be spent on details than ever before. The people designing our buildings, and especially those drafting the designs, must know what each and every line stands for. Diagrm. 29 provides a good example of a detail that required extra large illustrations for workers to fully understand the proper sequencing of materials. Without enlarging the detail and pointing out the various materials and methods of construction, we were certain that the people looking at our drawings could not understand, comprehend, and build the building the right way. We learned a lot about our workforce that week. We learned that we have to provide a lot of enlarged details to get complex walls built right.

Poor construction can take many forms. For every job that's done, there can be many wrong ways that it can be done. Backwater laps in waterproof membranes can lead to water intrusion. Laps in flashings and membranes should be made from the bottom up so that falling rain can drain over the previous layer at the laps and not behind the previous layer. The enlargement helps us to understand the importance of all these lines and words.

Corners can be lapped wrong, metal can be fastened wrong or cut wrong, and there can be countless other errors. The best means for prevention of improperly installed materials is to hire experienced, well-trained installers. Those installers need the right materials, at the right time, and in the right sizes. Then there should be a quality-control process, such as frequent walks by experienced observers such as general superintendents and trained inspectors. Many owners or developers hire specialists to observe projects during construction for good waterproofing practices. If the architect has a contract for full time, on-site construction administration, that should help with the quality review and observation process. Section 6.13 in Section 6 focuses on quality control during construction.

Membranes damaged during construction

Roof and wall membranes can be damaged during construction. They often get installed long before all the work around them is complete. Other workers may be less than careful working on or around a membrane. Roof membranes probably take the worst abuse. People may leave nails lying around, and others may walk on them. Nail or screw heads can easily punch holes in a membrane.

Sometimes we have welding that occurs above a membrane. There may be a torched-on cap sheet, during which AIBs can be damaged or melted if nearby. Scaffolding may be assembled and rolled around on the membrane. Some of these scaffolds have sharp corners that may puncture sidewall flashings or membranes. Other workers may fasten their work to or through a membrane. Some of these membranes may be difficult to patch, whereas others, such as a good self-adhesive membrane (SAM) or ethylene propylene diene monomer (EPDM), are relatively easy to patch properly.

Contractors and designers need to work together to specify the right roof membrane for the sequence of construction. If they know that the dry-in or base sheet likely will be damaged by workers performing a series of applications on scaffolding, for example, they should make sure that future plies are going to go on.

This is a benefit of three- and four-ply membranes. No matter what the intentions are, it can be difficult to protect a membrane if masonry is installed above it, say, on a side wall, for example. A roof membrane with a bunch of patches is not as reliable as a roof membrane that no one punctured while working above it.

Poor joint geometry

Joint geometry is a term we use to describe the physical shape of the path rain water would have to take to get into a wall. Poor joint geometry allows water to get behind flanges, sidings, or any finish material more easily. Membranes can be installed improperly, flashings omitted, trim installed at the wrong depth in the wall, etc. There are many ways that the manner in which the details are installed can permit easy entrance of water (see Diagrm. 32). Joint geometry is important to keep out normal water. By this, we mean the way the joint is constructed physically. In the macro sense, this can be divided into positive and negative detailing.

Negative details are developed with the fewest number of pieces and often rely on sealants to close off the joint to the weather.

Negative details often expose all the fasteners and structural members to view.

Post and beam framing is an example of negative detailing. Positive details, in contrast, typically don't expose connections to view and use more applied pieces of trim. There are pros and cons of the two different methodologies. Negative detailing typically has a lower initial cost and relies on sealants to keep out the weather. This often leads to higher maintenance and upkeep costs. Positive detailing typically has a higher initial cost and lower maintenance costs. While both methods can work, we observe that positive details tend to keep out wind-driven rain better than negative-detail joints. The down side is that if not detailed, installed, and maintained properly, positive-detail joints can create places where water can be trapped and find its way into the building over time.

Positive and negative detailing both have their places in keeping with the style and expression of the architectural concept. Traditional architectural styles such as shingle style, colonial style, and Mediterranean style typically have used positive detailing. Pieces of stone, stucco, wood, or metal frequently cover the voids between materials and planar surfaces.

We believe that well-conceived positive detailing can be the most effective at keeping water out of our buildings located in wet or humid regions over the long term. Details that place a piece of material over potential voids along a window jamb and head have the best success in preventing wind-driven rain from entering the building envelope. Similarly, we should use positive detailing at the bases of walls. Trim shapes for a window or door sill should slope away from the building facade-first down, then out. Similarly, positive detailing can be used at other types of joints as well. Positive detailing at the slab edge or top of a wall, for example, can take on many forms. In each, the objective is the same: Make it harder for water to get behind the membrane(s). Our idea of good detailing is to make wind-driven water lose energy by making it oppose gravity, change direction, or both. At the very least, we want to slow it down and make it change direction. Except in the most extreme conditions, water will not enter a detail horizontally, turn vertical, and then travel more than a few inches upward. This is the basis of most good positive detailing. Block the easy way in. Make the water lose energy, change direction, and go uphill. Then, by having a vertical leg that's taller than the water will climb, we effectively keep it out of the building. Along the coastal areas, that vertical leg on flashing is preferred to be a minimum of 12 inches; in lower-wind-speed zones, 8 inches may suffice. For window sill pan flashings 2 inch minimum is preferred on the interior vertical leg.

Beyond this overview, there is the micro-geometry, that's , the detail level.

Depending on the system chosen, this can take on many different forms but will have features in common. The idea is to keep water from getting behind the waterproof membrane. Whether it's the paint on the face of stucco or wood siding or a sheet membrane several layers in the wall, the big idea is the same. The challenge is to keep (predominantly) liquid water outside the membrane. Metal and sheet membranes can be used in concert to keep water from getting behind windows, door, and louvers in walls. Sealants can be used to augment the whole, reducing voids between and beneath flashings or behind and around trim. If such measures are installed right, the water will have pathways to drain at the low point in the cavity/detail condition. Refer to Sections 2 and 4 for more on geometry.

1Building below finish grade

Despite many building codes requiring the finish floor be more than 6 inches above finish grade, we find many buildings don't meet this requirement. This should only result from conscious decisions of expression and not from a lack of coordination between site and building designers. Architects must instruct civil engineers as to desired spot elevations around the building perimeter. There is one building type where finish grade is intended to be elevated above finish floor (not including basements, etc.). This is when buildings are intended to be earth sheltered. This decision should have resulted in special design details that would include special insulation and waterproof membrane details. In addition, many designers add a designed-in pathway for the water to drain out, such as a socked perforated drain in a rock exfiltration bed.

The only way these earth-sheltered buildings can avoid problems from condensation, vapor, or water intrusion is to keep temperatures and humidity in the wall under control. These measures often include an applied sheet membrane on the exterior face of the wall and closed-cell foam insulation.

If the finish floor is constructed below finish grade, gravity can make it easier for water to cause problems in the wall. To make matters worse, subterranean insects can erode the building protection system. Good design will only result in finished floors less than 6 inches above finish grade only when absolutely necessary. At accessible doorways, for example, walks should be designed at about 3/8 inch below floor elevation. Exterior walks begin to gently slope away from that required elevation when beyond the door area so as to maintain the 6-inch code-required offset.

Hydrostatic pressure

Additional measures must be taken to prevent hydrostatic pressure from introducing water into occupied spaces. In many coastal regions, there are areas that typically are well above the groundwater table. As a result of seasonal conditions, the water table may rise temporarily. Some soils create perched water tables, artificially keeping water locally higher than the average water table in the surrounding area. When the ground has more water than can be absorbed, it seeks relief. Often the rise can exceed 2 feet in elevation. This water will seek relief through even the smallest microscopic voids in concrete floors and walls.

There are several methods for preventing migration through walls and into a conditioned space, but the best protection is to keep the water from getting past the out side face of the wall. Two of the most common means for preventing water from getting into a wall are bentonite mats and plastic- or rubber-based impermeable sheet membranes. Some builders prefer the bentonite where the moisture levels are somewhat constant. Others rely only on the impermeable sheet membrane.

One of the inherent challenges is to prevent any punctures of the membrane.

Pipes, conduit, and other required penetrations will need to be sealed properly according to manufacturers' recommendations. Whichever system is chosen, if water does find a way in, there is likely to be a void in the system. That void must be dealt with. One proven method is to inject grout into holes that were drilled in the wall or floor slab near the apparent source of the leak. Another method involves the application of crystalline coatings that change the chemistry of the interior concrete to reduce water transmission.

Even well-intentioned maintenance procedures can result in hydrostatic introduction of water at the slab edge. Some maintenance practices include frequent pressure washing of walls and walks. The proper angle for the wand would be close to the wall so that deflected water moves away from the wall. In most cases, the pressure wand is located so as to spray toward the wall, potentially degrading sealants and reflecting water into the wall cavity.

If maintenance plans are known in advance, the design team can develop a detail that will effectively prevent introduction of spray into the wall cavity.

Again, go back to good geometry first. There must be a way to reduce pres sure and velocity of the pressurized water spray.

Enlarged plan detail:

1. Structural Steel

2. Fireproofing

3. Light Gage Metal Framing

4. Insulation

5. Drywall

6. Densglass

7. Air Infiltration Barrier

8. Paper-Backed Lath

9. Stucco

10. Roof Flashing

11. Miscellaneous Metals

12. Roofing Membranes

13. Painter

Poor geometry at floor.

Detail as intended. [ 5/8" F.R.T. Plywd. A. I. B. ; S. A. M. ; S. A. M. Extend 2" Beyond Face of Glas-Mat Sht'g 6" Wide Strip of Glas-Mat Exterior Sheathing Fiber Cement Batten Fiber Cement Board 6" Wide Screen Mat'l W/1/8" Holes at BTM, of Rainscreen Membrane 1/4" Rainscreen Membrane ]

Enlarged detail at roof edge.

Photo of punctured side-wall roofing membrane.

Melted wall membrane from torch applied roofing.

Poor joint geometry at wall.

Negative detail relies upon sealant. If Water Gets in here, it may Enter the Wall Sealant here could Trap Water in the Wall

Positive detail keeps out wind-driven rain. Membranes and Flashing Direct Water Out, Away Sealant here is Good, Keeps Water Out

Geometry to reduce energy of rain. Slab Edge Recess Reduces Likelihood of Water Intrusion Material blocks Path of Water Finish Grade is 6" Lower than Finish Floor Sidewalk, Sloped Away from Wall

Design for earth shelter.

Enlarged detail at sill. [Sill Pan, Set in Sealant Counter-flashing Insulation and Membrane Drain Board]

Pressure washing.

Failing sealant.

Poor maintenance

No system or product lasts forever. Whatever the products used, there exists the need for maintenance, repair, or replacement. Some system components need more maintenance than others. Decisions made in material selections, methods of application, frequency of maintenance, and environmental forces all can affect the length of service of a waterproofing system. If we rely solely on the elastomeric coatings on our exterior stucco for water resistance, the wall surface will need recoating as the original paint loses its effectiveness.

Sealants used will need to be removed and replaced over time. Even terra-cotta roofing tile applied over a three-ply modified system will last only about 50 or maybe 100 years before it may begin to have problems. These problems typically manifest as failures at valleys, copings, or where movement, water, or sunlight may have affected the membrane. If the tile is nailed, the nails can come loose over time. If copper or lead flashing is used, it may rot as a result of deposits from animals or plant materials. Operation and maintenance manuals or manufacturers' recommendations should be followed in order to keep the system components working to their fullest capacities.

Poor maintenance can manifest itself in many different ways. If one area of a building is maintained poorly, it can result in other problems. If the air conditioning filters are not changed often enough, it can lead to condensate pan overflow or failure to cool or remove humidity from the conditioned spaces. This alone can cause bacterial growth.

If organic material is allowed to maintain contact with metal flashings (especially copper and aluminum flashing), the metals can degrade quickly. If the lawn sprinkler system is not well maintained, it can spray water into the building over time or cause hydrostatic pressure by creating an artificially perched water table. If vent fans aren't lubricated properly, extra moisture can build up in kitchen and bath areas. Poor maintenance in one area also tends to reflect on maintenance as a whole. When a building is new, everything usually works well without any care. It is typically after the first five years that things which have been ignored begin to fail. If the building heating, ventilation, and air conditioning (HVAC) controls are not functioning properly, the air-conditioning system may not function as designed.

Maintenance that may have good intentions can have bad results too. Untrained applicators may apply sealant where water is intended to drain, effectively damming water behind the sealant. Perhaps they used the wrong paint, applying an epoxy paint to the inside face of exterior walls, which can lead to condensation at that point in the wall. They may change HVAC system settings to try to save energy, resulting in high humidity in the building. We have seen countless mechanical equipment rooms with filters that have not been changed as recommended (even with a supply of filters lying up against the wall). This can lead to reduction in air volume and reduced dehumidification. Omitted filters or filter bypass can cause cooling coils to get dirty and reduce heat transfer, raising supply air temperatures. Perhaps the exterior wall was designed as a drainage mass wall to allow moisture in and out through the face at a controlled rate. Maybe the contractor used white stucco on the face with a 4.0 perm rating block sealer on the concrete masonry unit (CMU) wall below. After 10 years, the wall may have been discolored, or the owner may have gotten tired of pressure washing it. Maybe the painter used an elastomeric paint, effectively trapping water behind the coating and prohibiting drying to the outside. We have seen outside air grills closed off, heaters turned off, bypass valves closed off, foam sprayed on leaking roof membranes, and all kinds of other well-intentioned but short-sighted maintenance actions affecting envelope performance.

Reliance upon sealants

This is an area where we have seen a lot of localized water intrusion problems.

Since the science behind our industry has advanced so greatly in the past 40 years, the materials we have available today are far superior to any in history. Sealants have better adhesion and elongation properties and wider temperature ranges. We have begun to rely on technology more than in times past, to the point where sealants are being relied on to stop water. We see 30-story condo towers with 2-inch sealant joints as the only means of protection against water intrusion at window and door jambs. When coupled with the changes in design philosophy (more negative detailing) and increased labor costs, we can begin to understand the move toward reliance on sealants to solve design issues. "Beat to fit and caulk to match" has become a common attitude among builders.

With the better, more specialized chemistry in the makeup of sealants today comes an increased need for understanding. It has become more difficult to match the specialized sealants with each condition in a building. Designers must take care to specify the proper sealant product for the job, not just in color and number of years in the warranty period. Some of these sealants can not be used if they are to be in contact with certain other materials. Some react with copper, some with paint, and many of them with waterproof membranes.

Active ingredients may include solvents that react with paints.

The area and surfaces of the materials being sealed are important too. Many manufacturers will limit the gap being filled to 3/4 inch, whereas others can be used to fill a 3-inch gap. There are three forms of sealant joints, and the geometry of the joint is critical to the success of each. Sealants should be shaped like an hourglass in section to best maximize adhesion to end surfaces and to reduce transmission of forces in the bonds (see Diagrm. 40). Properties of sealants vary greatly, and the selection should be matched to the operating conditions and stresses. Section 4 provides an overview of sealant design. Some sealants can be driven over with a fork lift without compressing. Others will elongate more than 400 percent. Birds and insects will pick out some types of sealants. If the designer or builder relies only on sealants to close the void in a joint, he or she has to consider providing access to the location for future replacement. Sealants fail. Consider the maintenance crew, schedule, and skill set before you decide to rely on sealants. Flashings should be designed to protect sealant joints and to reduce exposure to UV light, wind, and the force of rain. Then, when the sealant fails, less water will get into the wall or parapet cavity.

Sealant shape.

Wrong material for the job

Too often the wrong material is used. Recently we heard of a contractor proposing a substitution request to use an air infiltration barrier in lieu of the specified waterproof membrane under asphalt shingles on a 3-in-12 pitched roof. Proper match of material for each job is very important. Some subcontractors want to use 15-pound felt as an air infiltration barrier. In some conditions, designers rely on details which allow water vapor exfiltration, whereas others don't . The design may call for vented sidewall roofing membrane, soffit vents, ridge vents, AIBs, or a series of materials used in concert. Some contractors accidentally omit the vents or use the wrong roofing membrane. Some may try to rush the job and forget to order a long-lead item far enough in advance. This can lead to the use of substitutions that are not equivalent to originally specified materials, or worse-omission of a key component.

We have heard of subcontractors installing foil-faced fiberglass insulation where unfaced insulation was called for. Others have used galvanized furring strips where pressure-treated wood was shown on the plans. In both cases, condensation occurred at the cool face, and bacterial growth began. The right material is important for every job, whether we are talking about major components such as the air conditioner or roof system or small items such as the right kind of tape or screws. Builders need to be detail-oriented. Designers have to know a lot about materials and methods. Both have great responsibility and , today, great liability. The two teams need to work together to have the best chance for success.

Contractors need to ask questions, especially if they see something that looks out of the ordinary. The way the question is worded will have an impact on the way the designer receives the question and ultimately answers it. Try not to make it sound like finger pointing or ridicule. It often helps if alternate solutions are provided, along with an explanation of what is perceived to be deficient in the original detail.

Architects often rely on guidance from specialists on many topics. Due to the complexity of the projects these days, building systems are getting pretty specialized as well. The complexity of the building envelope can cause even well intentioned installers problems. For example, let us imagine the design for a concrete block wall with stucco over lath on 15-pound felt. Assume that the wall was designed to allow moisture to penetrate the stucco and block, where the CMU was to absorb a limited amount of water and dry back to the outside after a rain event. Maybe it was designed as a mass wall with no insulation.

Specified paint was to be latex inside and out. Now let us imagine further that the builder wanted to improve the design. Maybe he or she changed the paint to enamel on the outside and epoxy on the inside (both vapor barriers). This would tend to increase the potential for condensation in winter or summer and could trap moisture in the wall. Not good!

Exposure to ultraviolet (UV) radiation during construction

Several products we use in construction are negatively affected by exposure to weather. Many roof underlayments and air and vapor retarders should be limited to less than 30 days of exposure to UV rays. The warranty may be voided, and the membrane could crack and fail sooner than usual. Manufacturers' recommendations typically state the duration and types of exposure that are acceptable without significant impact on the product's performance. Most roof underlayments rely on the final surface product to keep damaging UV rays from degrading them. If a membrane's exposure exceeds manufacturer's recommendations, you should remove and replace it. Putting a second layer on could lead to problems you haven't considered. Pay attention to flashings in relation to membrane placement. An exception might be a fiberglass roof dry-in membrane for shingles or a tile roof. We will typically use a 30-pound felt instead of the mini mal 15-pound felt if we know that it's likely to be left exposed for longer than 30 days. Then, right before the finish material is applied, a new overlay of membrane (perhaps 15-pound at this point) would suffice. You may need to remove and reattach the flashings after the new membrane is applied. The concern is that you are deviating from the original permeability of the system as designed. Perhaps that permeability is critical to drying of the ceiling cavity.

Ask the designer before changing the permeability of any components or adding additional layers.

Failed roofing products

This may be one of the most expected problems. Whether it's the ridge vent that came loose from high winds and tree branches or cracked, broken, or missing roof tiles (see Diagrm. 41), a roof needs to be considered a holistic system. If one or more components of the system are not working properly, the system is at risk for failure. For a big commercial project, there could be 20 or more components interacting that can affect the outcome. It can begin with uneven settling at the foundation. Perhaps the spans were too great for the roof beams or joists, causing too much deflection. There can be problems with the lightweight concrete cracking. If batched or applied wrong or if not engineered to limit problems caused by thermal expansion, the concrete may crack, causing a chain of events above it.

Cracked or missing roof tile.

The tapered insulation may have been applied too thick for the fasteners.

Insulation boards may not have been applied properly. Perhaps it was raining or the slurry was sitting in the drum too long. Maybe the bag mix got rained on previously. Maybe there was a loss of power, and materials were not placed in a timely manner. The project may have been designed for 90 mile an hour winds and seen 125 mile an hour wind-driven rains. Perhaps the base sheet was applied too early, trapping excessive moisture under the membrane.

Maybe the wrong type of decking was used. The basis of design may have been vented metal decking, and it may not have been installed as such. Perhaps the crew installing the flashings went to lunch, and another crew came in to finish without sufficient knowledge of the product. Maybe it started raining during the mopping-in of the roof plies.

There are countless reasons why the system can fail later. Perhaps a bad batch of product was manufactured that month. Some of the rolls of material could have been stored improperly, causing flat spots in roll goods that prevented full flat adhesion. Perhaps the vents were not installed properly.

Maybe there were skylights that showed up late and got installed out of sequence. This can lead to membrane lap issues, patching, and potential problems. Maybe the roof curbs were installed 1/2 inch too low. Perhaps sill pans were damaged during installation or holes were drilled in them that went unnoticed.

Sill Pan damaged during construction.

There can be inadequate ventilation in the roof cavity; maybe the birds picked out all the sealant at the precast copings. The masons may have punctured the membrane with rolling scaffolding. Maybe everything was done according to the manufacturer's recommendations, and it still failed. Perhaps the primer used to seal the seams had been stored in too much heat. The best way to pre vent roof leaks is by paying attention to details and executing the installation to the best of everyone's abilities.

Reliance on coatings instead of membranes

During the late 1980s, we saw an increase in energy costs that led to an increase in the use of insulated roof coatings on low-slope roofs. You can find them on many schools and commercial buildings, often applied directly over tar and gravel systems. The old tar and gravel roof may have been leaking.

There could have been localized patches. The application of foamed-on roof coatings had two common immediate results. It lowered short-term operational costs as a result of the added insulating value. This was achieved by lowered cooling and heating bills. It also temporarily reduced roof leaks.

The down side of this was often not discovered for a few years. Many of these roof coatings used a two-part foam that formed a skin where exposed to the air at the surface. Unfortunately, some of these foams were not fully mixed during application. This resulted in a continuous expansion of portions of the foam.

The off-gassing of the curing also created bubbles above the roof. These bubbles eventually exceeded the material's elastic properties and popped. Some of these foam products are not really a closed-cell foam, meaning that there were small pathways for water to migrate through the foam. The water would find its way down to the original roof. If there were voids or failed patches in the original roof, this water would find its way into the ceiling cavity. It would be impossible to tell from below where the membrane was leaking.

Many building owners were forced to keep patching the foam topping by cutting out a portion of the affected area of foam and reapplying the same product. As a result of the physical nature of the system, other patching products have a difficult time adhering to the silicon skin. If the roof membrane were leak-tight prior to application of the foam, the building would not be experiencing these problems.

There are countless other examples where a coating is used in lieu of a membrane. Generally, membranes perform better than coatings. A few examples are below-grade exterior wall membranes and flat-roof systems. In exposed, accessible flat-surface applications, sheet membrane system applications place less importance on the performance of the installer than liquid applied coatings. For hard-to-reach places or horizontal areas with a lot of corners, liquid applied coatings depend less on the skill of the applicator, and are therefore utilized.

For sealing roof penetrations, the traditional solution was to use pitch pans filled with liquid roofing products such as hot tar or modified asphalt. New liquid products have much better long-term performance, such as the hybrid silicon and elastomer compounds. Many waterproofing experts still prefer metal flashing applications over liquid-filled pans. --- shows a poor example of a pitch pan used to seal a roof penetration. Sealants were added to the liquid applied roofing product as leaks were observed over time. Details like this are why owners prefer a properly installed penetration with sheet membranes.

Pipe penetration detail using a pitch pan and collar flashing.

Sealant Draw Band Watertight Sheet Metal Rain Collar Overlapping Penetration Pocket Sheet Metal Pitch Pan, Soldered/Welded Watertight (4" [102 mm] Min. Height 4" [102 mm] Min. Flange, Set in Roof Cement Over Field Plies, Prime Flange Before Stripping Multiple-ply Membrane Stripping Plies Multiple-ply Modified Bitumen Roof Membrane Coverboard Insulation Thermal Insulation Roof Deck; Approx. 1/4" [6 mm] Clearance at Corners Pourable Sealant Non-shrink Grout Roof Cement or Sealant at Penetration to Membrane Juncture Optional: Wood Nailers; Varies Depending Upon Size of Penetration

Photo of pitch pan as installed.

A series of bad decisions and /or other forces

Sometimes failures can be the result of bad decisions. We may specify the wrong product or apply the wrong detail to a condition. There have been designs that worked in one location that get imported into a project located in a different climate. If this happens in the early stages of the design process, there should be a system of checks and balances in place to prevent the poor decision from being built. Other examples could include finish grade above finish floor (without proper detailing), omission of crickets on roofing against vertical surfaces (such as chimneys), improper flashing design, lack of protection above windows and doors or louvers, inadequate ventilation, undersized air-conditioning equipment leading to a negative-pressure building, bad value engineering, etc.

There can be hundreds of reasons for a poorly performing building. It usually requires a combination of bad decisions and poor construction to create an indoor air-quality problem over time. Let's make up an example of decisions made in the process of design that could lead to a problem building. In our make-believe project, let's imagine a $40 million mixed-use building. Let us imagine that it's to be built on the Atlantic Coast . During schematic design, it's detailed using a primary structural steel post and beam system with 3 5/8-inch light-gauge stud exterior infill walls. It is assumed to have 3 1/2 inches of insulation in the walls, exterior fiberglass sheathing, vapor barrier, air infiltration barrier, and rough stucco over lath.

It was designed to use long overhangs on a hip roof to shade the east and south glass sliding doors and walls. The mechanical design was done assuming insulated tinted glass, R30 minimum roof insulation, and existing vegetation to block late-afternoon sun from west walls. The developer wanted to have gas water heaters with solar cells.

Let us imagine that the cost of construction went up 15 percent during the next four-month period of design. The developer already pre-sold the units based on schematic estimates with a 4 percent escalation estimate built in. Does this sound possible or maybe even familiar up to this point? Our pretend developer made the decision to try to cut 10 percent of the initial cost to make up a big chunk of the escalation. It seems that the price of steel went up the most, so the project changed to load-bearing concrete block exterior walls. This only saved 6 percent, so the team next had to save on something else. The next decision affected the roof. Instead of three-ply modified bitumen, the contractor changed to single-ply EPDM roofing and saved another 2 percent of project cost. One more value-engineering offer accepted was to change from rough three-coat to a new one-coat stucco system. The developer decided to pay the last 2 percent out of his 5 percent contingency budget (this is what contingency lines are for, isn't it)? At the end of design development, the team had the bidders go through the pricing check again. It seems that the more completed scope shown on the design development documents cost another $1,500,000. Now what can the team do? More value-engineering (cost cutting) decisions were made. The first one cut back the roof overhangs, and the second deleted the furring, vapor, and air infiltration barriers on the exterior walls, placing the one-coat stucco right on the block walls. The trade-off is to rely on a high-quality elastomeric paint to limit moisture in the building.

Guess what! These changes were not made known to the mechanical designer, who instead was asked to try to cut a few hundred thousand dollars from the air-conditioning system costs. Since he had oversized the coils, the designer agreed to reduce the tonnage by a half ton per unit. Insulation on ducting was reduced from 2 to 1 inch on supply ducts. Insulation was reduced to R20 aver age in the roof. Do you see a pattern developing here? The project reaches the 100 percent contract documents phase and goes into construction just 3 percent over budget. The developer decides to proceed knowing that he might have to pay the overage but commits the $300,000 out of his contingency budget, leaving him just about $50,000 in contingency remaining.

During the subcontract award phase, the contractor realizes that he didn't cover all the underground piping scope on the civil and plumbing drawings. So the contractor's contingency budget is almost gone too. The mechanical con tractor offers his own value engineering (VE), offering a savings of more than $350,000 to go to a lower-cost, lower-seasonal-energy-efficient-ratio (SEER) system instead of the designed system. Things are looking better to the con tractor, who was worried about his rising costs affecting his profit margin.

What else can go wrong? Now it seems that the roofing contractor can't bond the job. The second-low bidder was $400,000 higher than the apparent low bidder. It seems that the roofer was selling his business and used the job to sweeten his selling price to the ultimate buyer. Things were starting to back up on the job site, and finally, the contractor and owner were forced to take a hit and award the roofing to the second-low bidder. The drywall contractor is pushing the schedule, needing to maintain the original schedule to meet other commitments. The window sub contractor was late getting his submittals together. As often happens, a huge summer storm is approaching. The roof sheathing is almost done, and the roofer hasn't even gotten his contract signed yet. The general contractor decides to proceed with the roof sheathing and dries it in with his own staff of framing carpenters.

In order to maintain the schedule, the general contractor authorizes the drywall subcontractor to begin hanging drywall. The special-order insulated windows are still eight weeks out. The contractor submits a substitute window that he can get in two weeks. The stucco contractor starts applying stucco to the exterior block.

The storm hits, and it rains for four days. Only a little of the drywall gets soaked when a portion of the dry-in membrane comes loose and blows off. In another corner, the window openings allowed wind-blown rain to soak the dry wall stacked on the floor. Are the warning flags going up yet? Before now, every experienced project leader should have already become concerned. An entire series of decisions is combining with natural forces to create potential future problems.

Rather than continue to follow every step of the way, let's jump to the conclusion. The first year there were no big problems reported. A few windows leaked, and one roof leak occurred during a tropical storm. The builder takes care of them because the building is still under warranty. A little caulk and some roofing cement later, things seem to be going well. Then the trees died.

It seems the roots were cut during site utility work. The trees were replaced by 4-inch caliper oaks and 20-foot palms. Obviously, they don't provide much shade. The next summer was a hot, humid summer. The temperature stayed over 98ºF for three straight days, and the humidity was 100 percent. Then the rainy season started. Did we mention that the cheaper windows used were not insulated? To make things worse, the stucco installed on the parapets damaged the single-ply membrane. The flashings were not put in the right sequence of construction, so when the rain came in sideways, it overflowed the flashing and soaked the roof insulation. The mold started growing in the walls and around the windows on the exterior wall surfaces. When power was lost for three days, the bacterial growth was accelerated. When the owners got power back, the undersized air-conditioning system could not get the moisture out fast enough. Guess what happened next? The building owners sued the developer, builder, and architect. You can see where a series of decisions made during the heat of the construction process can lead to future problems. This is where a system of checks and balances can help to prevent catastrophic failure. In many projects, the inclusion of a water-proofing consulting firm to the processes of design and construction can reduce or even avoid such disastrous results. At a minimum, have a peer review of your planned details reviewed by someone with years of proven experience in the building type and climate. The relatively small investment in review services prior to construction begins may prevent time and money lost later.