Building Envelope Design: Intro and Selecting the Right Contractor/Firm

INTRODUCTION

The way a building looks is up to the designer. The form, shape, size, color, and fenestrations all come together to create what we see and what we touch and feel. We presently have more choices of materials available for the building envelope than ever before. Some designers choose to design from the inside out, framing views of the site. Others prefer to work from the outside in, letting the expressive form dictate where openings in the envelope occur. Individual expression is the norm.

Some buildings will be large; others will be small. Some will have flat (low slope) roof forms, whereas others may have 12-in-12 pitch or more. We may see punched window openings or glass curtain walls. The options are endless.

We are limited by our clients' budgets, the amount of time and materials avail able, the skills of our workers, and by our imagination.

In contrast to this, the conditions we are designing for have much more commonality. Regardless of where we are, certain physical principles are constant.

Gravity doesn't change much from Helsinki to Helena. Gravity stays relatively constant from summer to winter. It is one of the most constant of all the physical forces acting on our buildings, and for this reason, it's important to take gravity into consideration in all of our envelope design decisions. Wind and water are two more basic common elements of our physical environment.

Wind is the result of cyclic heating and cooling of our oceans and continents as a result of interaction with the sun as our earth rotates. Water makes up three-quarters of our planet. Water is present in all three physical phases in different parts of the planet at different times. It requires energy to change the temperature or phase of water or anything with mass. Velocity, acceleration, momentum, potential, and kinetic energy-all these terms describe real physical properties that affect the building envelope. The laws governing them don't change from Austin to Zimbabwe, just their values.

The evaporation of water from rivers, lakes, and oceans has a huge influence on our built environment. Evaporating water forms clouds, which are the result of liquid water changing phase and turning into gas (water vapor). This phase change reduces the temperature of the remaining water. Warmer air rises because it's less dense than cool air. Temperatures in the upper atmosphere are lower than those at lower levels. When vapors condense in the cooling clouds, they turn from gas into liquid rain that's carried by the wind and drawn back to earth by gravity. If it's cold enough, the droplets change into solid water in the form of snow or ice. This is the way it has been for millions of years.

Designers in a cool climate make different decisions for the building envelope than those in a warm climate. It is logical, then, that designs for a beach house in a hot, humid climate such as Florida are different from those for a mountain chalet in northern Canada. They both share the same approximate gravitational pull. We would expect the two to have vastly different roof and wall sections, insulation, and more. We would design the chalet for seasonal snow loads and the beach house for occasional hurricanes.

We feel that it's logical and appropriate, therefore, to discuss principles in this guide to the building envelope not only by system but also by climate. We have tried to provide a systematic approach for looking at the building envelope that will be of value regardless of the environment for which you are designing.

You can see from the Table 4-1 that temperatures vary greatly from location to location. The other thing that we would like you to notice is the difference between the average monthly low and high temperatures and the recorded lows and highs. Which should we use in calculations? If our insulation and /or mechanical systems are not sized to handle the extreme temperatures, what problems might we expect? How can we hope to avoid reaching the dew point in the wall or roof cavity? This is why we recommend that you hire a good team of professionals to design and build your buildings. Together you can make informed decisions throughout the process of project planning, design, and construction that can result in a completed project that will resist the elements for the long term.

SELECTING THE RIGHT FIRM

In the process for a building described earlier, the program was completed in the pre-design phase. The program is usually done by an architectural firm, and it does not need to be the same firm that will be doing the design. In some cases it will have been determined early on that the same firm will do the design. Two good reasons for this are continuity and time. With the same firm, there is less of an opportunity for lost continuity, and relationships that have been established can continue. Any information passed between participants in the program will be retained in design.

If there is time to be gained by not interviewing and selecting another architect and engineering (A/E) design firm, this might be another good reason to stick with the same firm. Some firms do a better job of programming than they do of design. There are a multitude of reasons why any project manager would do things differently in two different project situations.

As in most long-term relationships, there needs to be a good fit among individuals in the decision-making positions. We have heard of architect selections that have been made based on who the owner would most like to have as a dinner guest. When you think of all the hours that will be spent together and the hundreds of decisions that need to be made together (assuming that all the short-listed firms are nearly equal in competence and experience), then this may be as good a selection criterion as any. When you think of the hundreds of millions of dollars that may be at stake, you might make the selection based on logic or a proven track record of delivering complete documents.

One prominent client (the world's largest entertainment company) chooses to hand many of its development projects to one design firm and has been doing so for more than 15 years. When we asked why, we were told that their documents are more complete than those of any competitors. By getting complete documents, the developer has had far fewer change orders during construction.

This has several important benefits. Most important, it allows the developer to tie up less money for contingencies. The second factor was reported to be lower operating and repair/replacement costs as a result of good design at the detailed level. We are talking about building envelope performance as it equates with operation and maintenance. These are powerful reasons for selecting that same firm over and over.

You always should reach a comfort level with the design firm before signing a contract. The same goes for a design firm having a comfort level with the owner.

First-time relationships can be troublesome, and references may never tell you the full story over the phone. Conversely, they may tell you that the contractor or owner was not honorable when, in reality, the relationship was soured by the person you are talking to in checking the developer's references. First impressions can be right more often than not, but we wouldn't want to be haggling later over an interpretation of a clause in the contract with a developer that was trying to get the designer to pay for contractor's errors. We have found that the people you feel are generally treating you fairly in negotiating a fee will treat you reasonably throughout the relationship. This is why so many architects and builders like to have repeat business. You know what you can expect.

There are two other ways that architects can be selected. One is based on the fee.

Some owners will select the A/E team with the lowest fee. This can lead to a successful set of documents with no problems, or it can lead to the least amount of time being spent on the fewest sheets by the least experienced and qualified firm. This can lead to a series of unanticipated changes which could result in significant construction change orders.

The other common traditional means for selection is based on design competition. Some projects are awarded to the firm that comes up with the best-looking model or drawings. In our experience, this accounts for fewer than 2 percent of all projects. If selection is made based on a design that fulfills the building program, it can result in a terrific solution. If, on the other hand, selection is based on a "beauty contest" held before the program is started, it may not be so wonderful. Trying to squeeze a program into a predetermined form does not often result in a functional product for operation. For most client groups, it's a good idea to choose a firm with local participation, a local branch office (at a minimum), and local project management talent. This will make it easiest for timely responses and on-site representation. You could choose a firm based on merits and attitude or relations and then challenge the firm to come up with an acceptable form based on the program. Provide the firm with a good program, complete with image concepts, and let it come up with several quick solutions.

In this way, you will have improved your chances of getting an aesthetically pleasing form from a firm in which you have confidence.