FUNCTION of Interior Design

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Function is the requirement or set of requirements a detail must meet based on its basic purpose. E.g., a doorframe must provide support for the door, conceal the rough opening, provide a way to stop the door swing, and provide a way to latch or lock the door. If the opening is fire rated, the frame must also be rated along with the other components of the opening. Although related, function is most often independent of design intent, constraints, and constructability issues. In the case of a doorframe, the door must be supported by the frame regardless of the design of the opening or constraints such as local regulatory requirements or the project budget. This section reviews some of the common functional requirements of details and how they can be met.


Details are often used to conceal other construction or simply as a decorative surface. E.g., a wood base hides the joint between the partition and the floor. A coat of plaster provides a smooth finish over a rough concrete masonry wall.

In many cases, a concealing or finishing detail is simple, with few requirements other than direct application. In other situations, the concealing detail may be an integral part of the detail it covers, requiring the detailer to consider requirements such as fire resistance, durability, connections, movement, and tolerances. There are three variations of concealment and finish: covering substrates, covering joints or connections, and hiding mechanical and electrical services.

Covering Substrates

Covering a substrate is the simplest type of concealment and finish detail. It can be as straightforward as painting, applying wallpaper, and laying carpet, or more complex such as hanging thick stone panels on a high partition. However, even the simplest material application must take into account concerns such as the limitations of the material, the proper type and preparation of the substrate, and material durability.

Most designers and architects consider the requirements of applied materials to be specification items. Although they are communicated in writing in the specifications, they are best dealt with during the early stages of detail design and development. By reviewing applied materials early in the process, the designer can prevent problems, develop useful information for the specification writer, and coordinate the efforts of the design team.

There are two detailing responses for covering substrates.


To minimize costs and speed construction the number of individual steps required to apply a

finish should be kept to a minimum. E.g., if a rough plaster finish is desired, it may be possible to achieve it with veneer plaster construction rather than a more complex three-coat plaster application. If the right paint is specified in the correct dry- film thickness one coat can be used instead of two coats.


In most situations, minimizing the weight, thickness, or size of the covering saves money, simplifies installation, and minimizes structural problems. E.g., using thin veneer stone as a wall covering requires a less rigid substrate than a traditional full-thickness stone application. It’s also faster and costs less. See ill. 1. Thick stone would only have to be used if the substrate was significantly out of plumb or if large, individual stone panels were required.

However, minimizing thickness and weight is not always desirable. When the functions of fire resistance, acoustics, durability, maintainability, and security are considered, a heavier or thicker covering may be required. The desired weight and thickness of the covering should be matched to the functional needs and approved by the client before detailing begins.

Covering Joints and Connections

In many details, there are rough joining methods or mechanical connections that should not be visible, either for strictly aesthetic reasons or for reasons of safety, security, or maintainability.

For instance, the joint between a carpet and adjacent tile flooring can be made without any covering, as shown in ill. 2(a), if the installer correctly turns the edge. However, it’s likely that the joint will collect dirt, the carpet edge will fray, and the edge of the tile will chip. Two simple solutions are to use a metal edge or cover the joint with a metal strip, as shown in ill.2(b) and (c). Although other solutions are possible, these are two of the simplest.

In some cases, however, the designer may decide to emphasize the joints or connections, making them a prominent design feature. While this may contribute to the overall design concept, it can create other problems. Complex and intricate details can collect dirt, dust, and debris and may require greater maintenance than construction where complex joining is covered.

There are three detailing responses for covering joints and connections.

ill. 1 Minimize weight/thickness of covering (a) full thickness stone application (b) thin veneer stone application 1-1/2"-1-3/4" (38-45) thick stone veneer double layer gypsum wallboard shelf angle base required thin veneer stone mastic applied bottom tile can be trimmed to follow floor line ±3/8" (10)

ill. 2 Covering joints stone or tile floor thin set on subfloor metal angle metal threshold wood blocking pad tackless strip (a) tile/carpet butt joint (b) metal edge (c) tile/carpet joint covered

ill. 3 Reveal joint covering fire-rated partition preformed reveal trim joint compound

ill. 4 Covering connections for safety (a) exposed fasteners (b) concealed fasteners The detail is improved by concealing the fastening with the handrail itself, recessing the screws, as shown in ill. 4(b). Rounding the edges of the wall bracket also minimizes dirt and dust collection and makes maintenance easier.


The strictly functional needs of a detail must be considered when deciding how to cover a joint or connection. These include the functions of fire resistance, acoustics, water and moisture control, durability, maintainability, and safety.

If fire resistance is required, the covering, in most cases, must have the same fire rating or flame spread rating as the construction or it must be part of a tested assembly, such as a premanufactured, fire-rated access panel. E.g., a reveal joint in a fire-rated partition would have to be detailed in such a way that the approved fire-resistant construction was not compromised. One way of doing this is shown in ill. 3, where an extra layer of gypsum wallboard provides the continuity of the fire rating while a standard reveal joint is mounted in a second layer of wallboard. Unfortunately, this detail requires the entire partition to be covered with an additional layer of gypsum wallboard, increasing cost and construction time.

Joints in construction assemblies that are designed to reduce sound transmission must be given special attention because even very small cracks in an otherwise well-detailed and constructed assembly can ruin its sound rating. Small joints and cracks can only be sealed easily and effectively with acoustical sealant, so any finish covering only conceals the sealant rather than providing the acoustical seal itself.

A covering in a wet area must be sealed against water penetration and itself be resistant to damage from moisture. In most cases, water-resistant covering materials include ceramic tile for continuously and intermittently wet areas, such as bathrooms and shower rooms. Materials such as high-pressure decorative laminate and solid surfacing are also used for occasionally wet areas such as countertops. In either situation, joints must be sealed against water because even small amounts of moisture can damage wood, finishes, and other construction.

Concealing joints and connections should be also made with a material that is both durable and easily maintained. Materials should be at least as durable as the surrounding construction, and the covering should be replaceable if it wears or gets damaged.

Finally, a detail should be covered or otherwise designed to reduce the likelihood that people will be injured. For instance, a handrail prominently fastened to a wall in a corridor with exposed bolts may create an interesting detail but poses both safety problems as well as maintenance problems. The detail shown in ill. 4(a) could result in cut fingers and torn clothing.


Once a method of covering a joint or connection has been selected, it presents its own problems of fabrication, including those related to the functions of connection, structure, movement, tolerances, and construction. E.g., a designer may want to use wood wainscoting and trim on a fire-rated partition that requires control joints. The detail must allow for movement of the partition as well as for the attachment of trim. One way to do this is shown in ill. 5. In this example, a piece of wood trim is screwed to only one side of the joint, providing a sliding joint. Deep rabbets in the trim allow the paneling to move with the partition, while the joint still provides the continuity of fire rating. In this detail, the paneling must met flame-spread ratings of the applicable building code.

ill. 5 Trim covering an expansion joint trim attached on one side of joint only expansion joint double layer of 5/8" gypsum board to maintain 1-hr. rating wood panel 1/2" (13) max. 5/8" (16)

ill. 6 Use removable coverings (a) access to equipment (b) access for repair and replacement Z-clip translucent panel removable cover magnetic catch removable stop


In many situations, the underlying joint or construction must be accessible for repair or replacement. Coverings should be detailed so that they are easily removable with simple tools and in such a way that soiling and physical damage are avoided or minimized. Making coverings removable also makes it easier to deconstruct the project to recycle or reuse individual materials.

ill. 6(a) shows a removable covering for a back lighted panel so that lamps and other electrical components can be serviced. The cover is hung with Z-clips at the top and fixed with a magnetic catch at the bottom. This cover is easily removed without the need for tools or special knowledge. ill. 6(b) shows a typical removable stop for replacing broken glass.

Hiding Mechanical and Electrical Services

One of the most common reasons to use a concealment detail is to hide building services, including mechanical ductwork, plumbing pipes and fittings, electrical conduits and wiring, light fixtures, and sprinkler piping. In addition to simply concealing the services, certain mechanical and electrical equipment must be accessible. This is particularly true for control devices such as fire dampers, fans, heating and air conditioning units, valves, electrical junction boxes, control panels, and similar equipment.

There are three detailing responses for hiding mechanical and electrical services.

ill. 7 Clearances for HVAC distribution equipment varies hanger for duct suspended from structure above flexible duct 8"-12" (200-300) typical ceiling line supply air diffuser linear slot diffuser rigid or flexible supply air duct varies, allow 2" (50) min.

2"-8" (50-200) one slot:

12"-14" (300-360) two slot:

14"-18" (460-500)


If a service does not fit into a particular partition or ceiling construction being used the building assembly can simply be made thicker or larger as required to accommodate the service. The assembly can be made larger in just the area where the increased size is needed or the entire partition or ceiling can be enlarged so there is a smooth surface.

The amount of size increase required is dependent, of course, on the service or services to be accommodated. Where space is limited, the exact sizes of equipment should be verified with the consulting engineers, contractors, or suppliers. Some of the clearance requirements for common mechanical and electrical services are shown in ill.7 through 3-11. Actual sizes of common plumbing piping is given. These clearances are approximate for preliminary detailing purposes. Exact clearances should be verified once specific fixtures or services are specified.

ill. 8 Actual pipe sizes coupling 3/4"-1-1/2" (19-38) larger than outside diameter pipe diameter, D; D allow approx. cast iron hub and spigot copper, steel and plastic gasket coupling on cast iron and plastic drainage pipe sizes.

ill. 9 Sprinkler piping clearances (a) concealed head drop from 2" main 9" (230) min. can be reduced by using a pendent head 3" (75) min. clearance 3" (75) min. clearance grooved fitting threaded fittings (b) pendent head offset drop from 1-1/4" main 12" (300) min. add approx. 2" (50) for concealed head note: all dimensions approximate depending on pipe sizes, coupling types, head types, and installation methods verify clearances required with larger pipe sizes hanger.


When several services must be accommodated near each other or when increasing a partition thickness is not practical a separate chase can be constructed. A chase wall between two back-to-back restrooms is one example of this detailing technique. Two rows of studs are used, separated by enough space to accommodate all the plumbing pipes and fixture hangers used for both restrooms. Another common example is a ceiling plenum, where enough space is provided between the structural floor above and a suspended ceiling to conceal all the necessary services. Some of the common alternatives to using separate chases are shown in ill.12(a) and (b). Solutions for horizontal services are shown in ill.12(c) and (d).


In some situations, the best approach is not to conceal services at all but to leave them exposed.

This generally only works for services in the horizontal plane above where a suspended ceiling would normally be. At this location, the services are safely out of reach and don’t interfere with the function of the space. If exposing ductwork, piping, and light fixtures is consistent with the overall design concept, this approach often reduces both cost and construction time, as well as minimizes the need for new materials and their embodied energy that would otherwise be added to the project. The services can be left in their natural state, painted black to minimize their appearance, painted bright colors to make them a design feature, or partially deemphasized by suspending an open grid as an open ceiling. One popular technique is to use a standard T-bar suspended acoustical ceiling grid without using any acoustical tiles and paint all the services above the grid black. The effect for people at eye level is that of a normal ceiling plane with everything below it lighted, while the exposed services are less visible in darkness.

If the mechanical services are a major design feature, exposing them can sometimes cost more than concealing them. This is because of the additional expenses of carefully planning their layout, accurate and neat installation, and additional finishing, such as painting.

ill. 10 Clearances for electrical conduit and boxes outside diameter, D; R coupling size varies depending on type; allow ± 1/2" (13) over conduit size (c) electrical metallic conduit sizes and minimum bends (a) 4 x 4 junction box (b) 2 x 4 switch box 1-1/2", 2-1/8" (38, 54) 2", 2-1/2" (51, 64) 4" (102) 4" (102) 2" (51) 4" (102) EMT size, in. (mm) 1/2 (13) 3/4 (19) 1 (25) 1-1/4 (32) 1-1/2 (38) Min. radius, R, in. (mm) 4 (100) 5(125) 6 (150) 8 (200) 10 (250) minimum bending radius EMT or IMC size in. (mm) 1/2 (13) 3/4 (19) 1 (25) 1-1/4 (32) 1-1/2 (38) Approx. diam. D, in. (mm) 7/8 (22) 1-1/16 (27) 1-5/16 (33) 1-7/8 (48) 2-3/8 (60) Approximate outside diameter of conduit EMT: electrical metallic conduit IMC: intermediate metal conduit.

ill. 12 Use separate chases (a) chase wall for vertical services (b) furred out chase for vertical services (c) raised floor for horizontal services (d) dropped ceiling for horizontal services


One of the most basic design and detailing parameters is responding to the basic size and movement capabilities of human beings or for the objects the environment serves. In most cases, human beings are the primary users of interior space but interior design may also be concerned with accommodating such nonhuman elements or scale such as factory processes, automobiles, animals, or sports stadia.

There are four detailing responses for human and object fit.

ill. 11 Typical clearances for recessed luminaires (a) incandescent downlight (b) HID downlight (c) compact fluorescent, vertical (d) compact fluorescent, horizontal (e) LED downlight (f) low voltage MR-16 (g) standard recessed fluorescent troffer (h) recessed parabolic reflector fluorescent Note: when space is limited, verify sizes based on specific luminaires specified

Base Dimensions on Human Size and Reach or Object Size

The size, form, and movement capabilities of humans have been extensively studied and published by both the military and private sectors. Two good reference guides for interior designers are Human Dimension and Interior Space and The Measure of Man and Woman: Human Factors in Design. Refer to the sources at the end of this guide for complete bibliographic information. These sources, as well as others, document the wide range of human dimensions both as averages and relative to percentile data. Other reference sources, such as Interior Graphic Standards, give similar, condensed data and suggested sizes for spaces and objects designed for human use.

Designing details for human use must take anthropometric requirements into account for construction such as cabinets, work surfaces, storage units, built-in seating, doors, kitchens, and stairs. Although many dimensional standards have been developed for most of these items based on average human size, many of them may not be the best for current human usage.

E.g., the standard heights of vanities and kitchen countertops are generally too low for most users.

Designing for objects or processes in addition to human beings can be a challenge because of the often con flicting requirements of scale or environmental requirements.

Recognize Differences in Age, Height, Abilities

Most standard dimensions for details are based on the average, adult, able-bodied human. In many cases, an interior detail must accommodate a wide range of users ho may differ in age, size, and physical abilities. E.g., a stairway intended for use by both adults and children should have two handrails at different heights. A detail with operating devices should be accessible to the disabled as well as others.

Provide Adjustable Details

When possible, design details so that there is adjustability for different people who may use the detail at different times during its life cycle. Adjustable shelving, tilting surfaces, and movable partitions are examples of adjustable details. Because of the added cost, adjustable details are not always possible unless the convenience, use, or number of people involved justify such a detail.

Provide Alternate Fits

When it’s not possible to provide adjustability in a detail, two or more options may be given to the users. E.g., providing two different service counter heights is a common way to allow access to both standing and wheelchair users.


There are two different types of safety. One is safety from accidental harm, such as trips, cuts, scraps, and falls, and the other is safety from intentionally harm, such as robbery, shootings, and terrorism. In many cases, safety from accidental harm is important enough that requirements have been codified in building codes and other regulations, as discussed in Section 2. This section highlights some of those and provides additional information on basic safety parameters for all details.

There are eight detailing responses for protection from accidental harm.

Use Nonslip Flooring

Some of the most common accidents in the environment involve slipping on stairs and ramps, as well as on flat surfaces. Details that involve flooring should use material that provides an adequate degree of slip resistance for the intended use. Tile, stone, terrazzo, and other smooth surfaces can be potentially dangerous, especially when wet or covered with grease or other slippery substances.

As discussed in Section 2, slip resistance is evaluated and specified with the coe fficient of friction (COF). A COF of 0.5 is generally considered a minimum value, with a minimum value of 0.6 for accessible routes and 0.8 for ramps.

Avoid Sharp Edges

Close to Human Contact Many details and standard methods of construction result in sharp edges and corners. These are unnecessary hazards to human safety and are easily preventable. Consider the height and typical movement of human beings near counters, work surfaces, upper cabinets, shelving, and other woodwork. Also treat corners near circulation spaces where people are likely to cut a corner. Corners can be rounded, chamfered, or otherwise detailed to minimize injury on contact. See ill. 13(a).

Hardware and exposed fasteners should also be selected and detailed to minimize sharp edges and places where people could catch clothing or scrape their hands or other parts of their body. See ill. 13(b).

ill. 13 Avoiding sharp edges rounded chamfered reentrant (a) smooth corners (b) protect hardware and fasteners exposed smoothed recessed countertop For finish materials, carefully consider avoiding the use of rough finishes close to where people may scrape their body against them.

ill. 14 Handrail con figurations 1-1/4"-2-3/4" (32-70) 1-3/4" (45) min. 5/16" (8) min. 3/4" (19) max. where recess begins 7/8" (22) max. 3/8" (10) min. minimum radius of 0.01" (0.25) 1-1/2" (38) min.

If handrails have a perimeter greater than 6-1/4" (160 mm), they must have a graspable finger recess as shown or a similar profile.

(b) Type II handrail alternate shape (a) Type I handrails 1-1/4"-2" (32-51) 1-1/2" (38) min. circular section 2-1/4" (57) max. 1-1/2" (38) min. non-circular section; perimeter min. 4" (102) and max. of 6-1/4" (160)

Provide Handrails and Guards When Necessary

Handrails and guards are required by both building codes and ADA regulations in most of the common hazardous locations, such as stairs, ramps, and elevated platforms more than 30 in. (762mm) above the adjacent floor surface. However, the designer should consider detailing handrails and guards when they may not be necessary by regulation, such as corridors, low platforms, or near three or fewer rises in dwelling units and sleeping units in Group R-2 and R-3 occupancies, and in corridors.

When handrails are used, they must be easily graspable and mounted far enough away from a wall to allow gripping. The IBC and ADA/ABA guidelines limit the size and shape of handrails. These are shown in ill. 14. In addition to a standard Type I handrail, the IBC now allows a Type II handrail where the perimeter is greater than 6-1/4 in. (160 mm).

These are allowed in group R-3 (residential) occupancies, within dwelling units in Group R-2 occupancies (apartments, condominiums), and in Group U occupancies that are accessory to a Group R-3 occupancy or accessory to individual dwellings in Group R-2 occupancies.

Design Stairs Correctly

A large number of accidental falls occur on stairs in both residential and commercial construction. As with handrails, stair design is largely governed by code and accessibility requirements, but these are minimum acceptable limits. The designer can improve on stair design by following several guidelines.

++ When possible, use riser heights slightly less than code maximums. A riser height of 6-1/4 in. to 6-1/2 in. (159 mm to 165 mm) is easier to traverse, especially for older people, and reduces fatigue on long flights of stairs. Don’t use risers less than 4 in. (102 mm) high.

++ Increase the depth of the tread beyond the minimum of 11 in. (279 mm). In addition to matching a corresponding decrease in riser height, a deeper tread accommodates larger foot and shoe sizes and gives firmer footing and a greater allowance for missteps. A depth of 12 in. (305 mm) is good with a riser height of 6-1/2 in. (165 mm).

++ Don’t use nosings with sharp edges underneath as required by code, and limit nosing projection to 1 in. (25 mm) instead of the 1-1/4 in. (32 mm) allowed by the IBC. Limit the radius of the leading edge of nosings to 1/2 in. (12.7 mm) as required by the IBC.

++ Don’t use open risers, even if they are allowed by the local building code or occupancy type.

_Maintain consistency in riser height from one riser to the next. Although the IBC allows up to 3/8 in. (9.5 mm) variation between the largest and smallest riser height or tread depth in any flight of stairs, keep the variation to a maximum of 3/16 in. (5 mm) between adjacent riser heights.

++ Provide a stairway width to accommodate the volume of people using it. For monumental stairs that are not part of the required width of egress, a minimum width for two people walking abreast or passing is about 60 in. (1525 mm). When wider than 60 in., monumental stairs that are not part of the required means of egress should have a handrail for each 60 in. of width, even if they are not required by the local code.

Provide handrails for both sides of narrow stairs, even if they are not required by the local building code.

++ For hard surface floors on stairs, use nonslip nosings and contrasting colors or materials so that the nosing is clearly visible. Avoid carpet or flooring patterns that may be confusing and make it di fficult to discern the edge of the nosing.

++ Provide a second handrail about 24 in. (610 mm) above the nosing line if children will frequently be using the stair.

++ Extend handrails beyond the top and bottom risers in residential applications where they might not otherwise be required, just as they are for commercial construction.

++ Avoid sharp edges in handrails, balusters, and walls along stairways.

Mark Full-Height Glass

Although the IBC allows the use of full-height glass adjacent to walking surfaces if it’s safety glazing, consider using a horizontal mullion, crash bar, or other clearly visible markings on the glass at eye level to prevent accidental collisions with the glass. If clear views are not required, textured or art glass can also be used to transmit light, while making the barrier obvious.

Avoid Single Steps Single steps can be unsafe. However, if one or two steps are used, they should be clearly marked with distinctive risers, treads, or nosings and provided with handrails. Consider using a ramp instead or adjust the change in levels to accommodate a minimum of three risers.

Avoid Slight Change of Level

Changes in level, no matter how slight, pose a tripping risk. This is especially true for children and the elderly. A change as small at 1/2 in. (13 mm) can be enough to trip someone. In most cases, accessibility regulations limit a vertical change in level to 1/4 in. (6 mm). Changes in level of 1/2 in. (13 mm) may be made but only with a bevel of one vertical unit to two horizontal units. If possible, make changes in level less than these maximums where they are required and use the same guidelines for residential occupancies and other locations where they might not otherwise be required by accessibility regulations.

Use Nontoxic Materials

Many materials used in detailing may contain harmful chemicals such as formaldehyde and volatile organic compounds (VOCs), as well as others. Adhesives, particleboard, and other panel products may contain formaldehyde and adhesives, and other finishes may contain VOCs. Refer to the section on sustainability later in this section.


All interior design projects require some type of security, whether as simple as a lock on the front door of a house or as complex as an alarm system and security barriers for a bank or government installation. In most cases, the designer or detailer does not develop security systems but may work closely with an architect or consultant to incorporate security measures into partitions, door opening assemblies, glazing systems, reception stations, security stations, display cases, and support for wall- and ceiling-mounted equipment. Before beginning the details, the designer should gather and understand all the requirements including the type of equipment that must be incorporated into the detail, and any electrical, communication, and data cabling requirements.

There are five detailing responses for protection from intentional harm.

Use Locks, Detection, and Intrusion Alarms as Appropriate

Locks and alarms are the simplest types of standard security measures to control access, protect property, and secure rooms or entire areas of a building. Locks can be as simple as a cabinet lock on a drawer or as complex as a system of card-reader-controlled doors monitored at a central supervision station. With information provided by the security consultant, owner, or architect, the interior designer can plan ahead to accommodate security devices and hardware to minimize their visual impact.

Design Physical Barriers for the Level of Security Required

Although standard interior partitions provide little protection from break-in or firearms, when combined with intrusion alarms they are often enough for most uses. If more security is required gypsum wallboard partitions can be reinforced or other types of partitions constructed.

ill. 15 shows some possible security partitions.

As shown in ill. 15(a), heavy-gauge steel studs can be used with security mesh to create a partition that appears to be like any other wallboard construction, with about the same thickness. Solid plaster partitions, shown in ill. 15(b), can be used, but they are more di fficult to construct. For very high-security partitions, reinforced masonry may be needed, as shown in ill. 15(c). In any case, the owner must inform the interior designer of the desired level of security before design and detailing begin.

Use Electronic Surveillance When Required

Electronic surveillance is the interception of sound and electromagnetic signals with remote sensing devices. When an owner requires security from this type of intrusion, a variety of methods can be used, which basically require building a "cage" of continuously conductive material that catches signals and conducts them to the ground. For most corporate needs copper foil or nonwoven fabric with electronically conductive metallic coatings can be used.

This is placed behind the finished wall surface so that it’s not noticeable. For windows, fine metal screens can be used, but special shielded glass is also available that looks like normal glass. Doors designed for radio frequency or electromagnetic shielding are also required to seal a room. In all cases, a security expert should be consulted for specific product specifications and detailing requirements.

Use Ballistic-Resistant Assemblies

If security from a ballistic attack rather than a physical break-in is required, ballistic armor can be used, as shown in ill. 16. This is fiberglass-reinforced composite material available in rigid sheets like plywood, in thicknesses from 1/4 in. to 1/2 in. (6 mm to 13 mm). It can be covered with various finishes or simply painted. Flexible ballistic armor is also available, which is covered with gypsum wallboard.

ill. 15 Security partitions structural steel studs security mesh welded to steel studs furring and gypsum wallboard base as required perforated steel sheeting welded to angle high-strength plaster base as required (a) wire mesh reinforced steel angle bolted to concrete floor finish coat of plaster steel plate anchored to unit masonry if required fully grouted concrete unit masonry reinforcing bars gypsum wallboard on furring (b) solid reinforced plaster (c) masonry

ill. 16 Ballistic protection partition ballistic armor panel steel or wood studs gypsum wallboard finish laminated over armor

Devise Space Plan for Supervision

Although not strictly a part of detailing, space planning can aid in a good overall security plan. E.g., spaces with similar security needs should be located together, if possible.

This makes it easier to enclose the area with physical barriers and well as minimizing the number of electronic devices required. Also, security personnel can be located in a central position with a clear line of sight to as many secure areas as possible. For minimal security, store clerks, receptionists, and other normal users can be located where they can supervise much of the space.


As discussed in Section 2, sustainability can be treated as a constraint if there are local or state regulations concerning materials, energy use, VOCs, and the like. In most cases, however, creating sustainable interiors should be considered an opportunity to create a functional, healthy, responsible environment. In this way, sustainability should be considered one of the basic functions that all details ful fill. Even if the owner of the facility is interested in applying for LEED certification, sustainability should be viewed as an opportunity rather than a constraint.

Sustainability, as a broad term, means meeting the needs and wants of the present generation without harming or compromising the ability of future generations to meet their needs. Sustainable design involves the design, operation, and reuse concepts that together can create functional, healthy, nonpolluting, and environmentally friendly buildings with out compromising practical requirements or human comfort. When evaluating details and products for sustainability, the designer should consider many individual criteria, including recycled content, recyclability, energy consumption, and life-cycle assessment, among others as described below.

Some of the criteria for evaluating how sustainable a detail or product is include the following. Of course, not all of the criteria apply to every detail. In addition, the designer must make informed judgments because some criteria con flict. E.g., aluminum has a very high embodied energy, but recycled aluminum has about one third the embodied energy, is plentiful, and the material can be recycled again after its useful life. The value of a lightweight, extruded aluminum section may outweigh the fact that it takes large amounts of energy to produce aluminum and it may not be a locally produced product. The amount of aluminum in a detail may also be so small in proportion to all the material in a building that the question is less important than other sustainability concerns.

There are 12 detailing responses for sustainability.

Detail with Materials That Incorporate as Little Embodied Energy as Possible

The material or product in a detail or used as a finish should require as little energy as possible for its extraction as a raw material, initial processing, and subsequent manufacture or fabrication into a finished building product. This includes the energy required for transportation of the materials and products during their life cycle. The production of the material should also generate as little waste or pollution as possible. Tbl. 2 gives some of the embodied energy requirements of some common building materials. When comparing proprietary products, the manufacturers may be able to provide information on the embodied energy of their products. Generally, products that are produced near the building site require less embodied energy because of transportation issues. However, the embodied energy in materials accounts for a very small percentage (some estimate about 2%) of the total energy requirement of a building's design and long-term operation.

Tbl. 2 Embodied Energy in Common Interior Detailing Materials Embodied energy Material Btu/lb. MJ/kg Detail elements lumber 1080 2.5 gypsum wallboard 2630 6.1 particleboard 3450 8.0 aluminum (recycled) 3490 8.1 steel (recycled) 3830 8.9 plywood 4480 10.4 glass 6850 15.9 steel 13,790 32.0 PVC 30,170 70.0 aluminum 97,840 227 Finishes stone (local) 340 0.79 clay brick 1,080 2.5 zinc 21,980 51.0 brass 26,720 62.0 copper 30,430 70.6 paint 40,210 93.3 linoleum 49,990 116 synthetic carpet 63,790 148 Source: Environmental Resource Guide To convert MJ/kg to Btu/lb, multiply by 431

Use Renewable Materials

A material is sustainable if it comes from sources that can renew themselves within a fairly short time. Some examples of products that meet this criterion include wool carpets, bamboo flooring and paneling, straw board, linoleum flooring, poplar oriented strand board (OSB), sun flower seed board, and wheatgrass cabinetry. However, as with all sustainability issues choices must often be made between con flicting facts. E.g., bamboo is a very renewable resource, but it must be transported long distances to the United States. However, bamboo so quickly renews itself that the transportation issue may not be as important as not using other hardwoods for flooring.

Use Materials with High Recycled Content

The more recycled content a material has, the less raw materials and energy are required to process the raw materials into a final product. Each of the three types of recycled content should be considered: postconsumer materials, postindustrial materials, and recovered materials. Postconsumer materials are those referring to a material or product that has served its intended use and has been diverted or recovered from waste designed for disposal, having completed its life as a consumer item. Postindustrial materials refer to materials generated in the manufacturing process that have been recovered or diverted from solid waste. Recovered materials are waste or byproducts that have been recovered or diverted from solid-waste disposal. Using recycled content products has two advantages. First, it reduces the need for the production of new materials. Second, greater use creates a better market for recycled products and encourages others to recycle, while lowering the cost.

When Possible, Use Products or Design Details That Can Reduce Energy Consumption

In addition to using materials with low embodied energy, some materials and details may help reduce the energy consumption of building operation. E.g., intelligent use of glazing can improve daylighting and reduce lighting energy requirements, as can the use of light- reflective materials. If a building has been designed for natural ventilation or solar energy, interior partitions, openings, and other finishes and details should not defeat the heating and ventilating systems designed by the architect and mechanical engineer. Although there are limited opportunities with detailing to affect the overall energy use of a building, the designer should consider the possibilities whenever possible.

Use Local Materials

Using locally produced materials reduces transportation costs and can add to the regional character of a design. Generally, local materials are considered those that are extracted, harvested, recovered, or manufactured within a radius of 500 mi (804 km) of the project. When compared with many traditional interior materials that are sourced from other countries, the use of local material can make a huge difference in the sustainability of a project.

Use Materials with Low or No VOCs

As mentioned in Section 2, volatile organic compounds are now regulated by the EPA as well as some states, notably California, which has strict limits on the VOC content of building materials and cleaning products, among others. VOCs are found in many indoor sources, including building materials and common household products. Common sources of VOCs in building materials and details include paint, stains, adhesives, sealants, water repellents and sealers, particleboard, furniture, upholstery, and carpeting. Other sources include copy machines, cleaning agents, and pesticides. Any detail should minimize or eliminate the use of materials with VOCs. The designer may even want to use materials that have a lower VOC content than required by EPA or local regulations. Refer to Tbl. 12 for a listing of some of the VOC limits on finishes and adhesives.

Use Materials with Low Toxicity

In addition to limiting VOC-containing products, materials should be selected that emit few or no harmful gases such as chloro fluorocarbons (CFCs), formaldehyde, and others. There are potentially hundreds of organic and inorganic chemicals that may be harmful to humans.

The California Office of Environmental Health Hazard Assessment has a list of 76 chemicals (current at the time of this writing) that the state regulates along with the chronic inhalation reference exposure level (REL) for each, in micrograms per cubic meter (µg/m3 ). These were developed as a result of California's Proposition 65, which was passed in 1986.

The Greenguard Environmental Institute also produces a list of products, chemicals in those products, and allowable maximum emission levels. Some of the common chemicals include VOCs, formaldehyde, aldehydes, 4-phenylcyclohexene, and styrene, as well as particulates and biological contaminates. In order to be certified, a product must meet standards after being tested according to ASTM D5116 and D6670, the state of Washington's protocol for interior furnishings and construction materials, and the EPA's testing protocol for furniture.

Design Details and Select Materials to Minimize Moisture Problems

If possible, materials should be selected that prevent or resist the growth of biological contaminants, mainly mold and mildew. Molds and mildew are microscopic organisms, a type of fungi, that produce enzymes to digest organic matter. Their reproductive spores are present nearly everywhere.

Mold spores require three conditions to grow: moisture, a nutrient, and a temperature range from 40 F to 100 F (4 C to38 C). Nutrients are simply organic materials, which can include wood, carpet, the paper coating of gypsum wallboard, paint, wallpaper, insulation, and ceiling tile, among others, that serve as a nourishing food source for organisms. Because nutrients and a suitable temperature are always present in buildings, the only ways to prevent and control mold are to prevent and control moisture in places where it should not be, or to use a material that does not provide a nutrient. For most details this is not a problem unless the detail is near a water or moisture source, such as a kitchen or bathroom cabinet, millwork in humid areas, or materials in pool and spa areas.

Use Durable Materials and Details

Materials that have a long life span contribute to sustainability in two ways. First, durable materials obviate the need to create new materials, reducing energy consumption and resource depletion. Second, durable materials need to be replaced less often, reducing waste problems.

As an added bene fit, durable materials generally require less maintenance over the life of a product or building. Even though initial costs may be higher, the life-cycle costs may be less.

Design Details to Simplify Maintenance

Details that degrade or break need to be maintained or parts need to be replaced, and as with durability, this creates the requirement for more materials and waste disposal issues. Details should also be designed to only require nontoxic and low-VOC cleaners.

Specify Materials and Design Details to Maximize Recycling Potential

Some materials and products are more readily recycled than others. Steel and aluminum, E.g., can usually be separated from other materials and melted down to make new products, reducing the embodied energy in the new products. On the other hand, plastics used in construction details are di fficult to remove and separate. Details should be designed to allow them to be dissembled easily for recycling, if possible.

- Tbl. 3 Sustainable Product Certification Programs Program Description BIFMA International Develops two standards for VOC emissions from o ffice furniture systems and seating as well as a furniture sustainability standard.

FloorScore of the Resilient Floor Covering Institute FloorScore program tests and certifies flooring products for compliance with strict indoor air quality requirements in California and that qualify for use in high-performance schools and o ffice building in California.

Forest Stewardship Council (FSC) International body that oversees the development of national and regional standards based on basic forest management principles and criteria. It accredits certifying organizations that comply with its principles. The FSC logo ensures that materials have come from well-managed forests and have followed the other FSC principles.

Greenguard Environmental Institute (GEI) Nonpro fit, industry-independent organization that oversees the Greenguard Certification Program that tests indoor products for emissions to ensure acceptable indoor air quality.

Green Label Plus program of the Carpet and Rug Institute (CRI) The Green Label Plus program is a voluntary testing program for carpet, cushion, and adhesive that conforms to California's high performance schools program. Carpet carrying the Green Label Plus mark is certified as being low-emitting.

Green Seal Independent, nonpro fit organization that develops standards for products in specific categories and certifies products that meet the high standards of the program.

Institute for Market Transformation to Sustainability (MTS) MTS is an organization that oversees the SMaRT (Sustainable Materials Rating Technology) program, which identifies sustainable products based on awarding points in the areas of (1) safe for public health and environment, (2) energy reduction and renewable energy materials, (3) company and facility requirements, including social equity, and (4) reuse and reclamation. Products are certified at one of three levels: silver, gold, and platinum.

MBDC Cradle to Cradle (C2C) The C2C certification program offers two types of product certification: C2C technical/biological nutrient certification that certifies that a material can be continually reused as either a biological or technical nutrient or a C2C product certification, which is a three-tiered classification of silver, gold, or platinum, based on the criteria of materials, nutrient reutilization, energy, water, and social responsibility.

Scientific Certification Systems (SCS) Under its Environmental Claims Certification program, SCS certifies specific product attributes such as biodegradability and recycled content. It also certifies environmentally preferable products (EPP). Another program is Indoor Advantage, which covers non- floor interior products. SCS also certifies well-managed forests under its Forest Certification Program.

Sustainable Forestry Initiative (SFI) The SFI program gives four different product labels to participating companies that meet the SFI requirements based on both environmental and market demands.


Design Details for Reusability

A product should be reusable after it has served its purpose in the original building. The product may become a salvaged material that can be reused in another project, such as a door assembly, or the component parts should be easily separated for recycling as discussed above.

E.g., details that can easily be dismantled with mechanical fasteners are often better than those that may require adhesive for connection that can destroy the component parts when disassembled or make it too di fficult to deconstruct.

For more information on sustainable materials and certification programs refer to Tbl 3.


Sustainability Issues Related to the Detailing Parameter Function

++ Question if covering a detail is really necessary. This minimizes the need for materials, avoids possible toxic materials, and makes it easier to deconstruct the detail for reuse or recycling.

++ Question the need to hide building services for the same reasons.

++ If coverings are used, make them easily removable for reuse or recycling.

++ Think "end-of-life" product responsibility from the start of design and detailing. This includes thinking of how the materials in the detail will be disposed of or recycled or reused.

++ Use nontoxic materials in details such as formaldehyde-free panel products, adhesives with volatile organic compounds, or plastics that may outgas harmful chemicals. Limit toxic fire-retardant materials.

++ Use materials that minimize organic material that could support mold or mildew if they got wet. If this is not possible, detail to control moisture penetration into the construction assembly.

++ Provide for multiple uses of the same construction element. Cabinetry, movable partitions, and similar elements can be designed for different purposes to limit the need for disposal of existing products and creation of new products.


The use of a buildings or leased interior seldom stays the same. If possible, details should adapt to the possibility for change over the life cycle of their use. In many cases, a detail may be so specific to a particular user or function that, when the use changes, the detail must be removed. In this case, the responses to the sustainability function of recycling and reuse apply. E.g., a serving line in a cafeteria would work for little else if the space were remodeled into a bank. However, in many cases the designer can anticipate change and design accordingly.

There are three detailing responses for change and re-locatability.

Design for Relocating the Detail with the Same User

In many situations, the same user may occupy the same space for a long time but may need to make occasional (or frequent) changes to continue the business. This is one of the easiest responses to implement because the basic physical environmental requirements usually stay more or less the same with the same user. Business o ffices are a common example of this situation, where changes to business needs, methods of operating, or personnel require a new arrangement of o ffices and support facilities. Movable partitions or demountable partitions are one of the common design responses to this type of need. Cabinets, workstations, storage units, and doorframes can be designed and detailed to make modification and relocation possible.

Other details, such as glazing, gypsum wallboard, or ceilings may not be easily relocated but may be designed to be simple, low cost, and easy to deconstruct.

Detail for the Same Function but with a Change in Users

Many times an owner or tenant will move and a similar user will occupy the same space for the same purpose. The existing physical con figuration may work for the new user with only minor modifications or just significant modifications to one part of the space. This happens often with apartments, condominiums, o ffices, retail stores, and even some restaurants. In these cases, basic details can be designed to remain structurally the same with the potential for easy modification of finishes. E.g., built-in display cases for a retail store can remain the same size and shape with lighting and adjustability but allow for a simple replacement of new shelves with a different finish for different merchandise.

As the needs and design requirements of a future user can only be roughly anticipated at the time of the original design, the detailer must make a best judgment concerning what may change.

Detail for a Change of Function of the Space with Different Users

This type of response is more di fficult to respond to because a change in user with a different function usually means a completely different environmental response. E.g., changing from a restaurant to a retail store requires a wide difference in design, detail types, construction, and finishes. In reality, the most the designer can do is detail common building element, such as door openings, storage cabinets, suspended ceiling systems, stairways, and the like so that they can be reused as much as possible.

ill. 17 Two-hour rated steel column enclosure heavy column corner beads required at each outside corner extra layer required when column is a lighter than a W 10 x 49 1-5/8" (41 mm) steel studs 1/2" gypsum wallboard face layer over 5/8" type X gypsum board base layer


In most cases, fire resistance is generally viewed as a constraint, as discussed in Section 2.

Unless otherwise required by the client, the designer seldom builds in more fire resistance than is required by the building code or the local fire marshal. However, for general safety of an interior, fire resistance can also be viewed as a basic function. As stated in Section 2, there are two basic concerns with fire resistance, the surface burning characteristics of finishes and the fire resistance of an entire assembly.

There are five detailing responses for creating fire resistance.

Use Noncombustible Materials in Details

A basic material is considered to be noncombustible when it meets the requirements of ASTM E136. For composite materials, the structural base must be noncombustible and the surfacing can be no more than 1/8 in. (3.18 mm) thick with a maximum flame spread of 50 when tested in accordance with ASTME84 or UL 723. Even if the building code does not require a portion or all of a detail to be fire-resistance-rated, consider using noncombustible materials.

E.g., if wood blocking is allowed, metal framing may be used instead.

Limit the Amount of Flammable Materials

The simplest way to create a fire-resistant surface is to specify a material that that has a flame spread rating below 25 (Class A) when tested in accordance with ASTM E84. Most commercial interior finish manufacturers provide materials that have a Class A flame spread rating. If not, consider applying a fire-retardant coating as described below.

Use Applied Fire Retardants When Required

When required in a detail, applied fire retardants may take four basic forms: encasement with a fire-resistant material, spray-applied fire-resistive coatings, intumescent materials, or coatings.

Encasement is generally with one or more layers of gypsum wallboard used to give a steel column or beam a one-, two-, or three-hour fire resistance rating. Approved methods of doing this are given in the Building Material Directory published by Underwriters Laboratories, the Fire Resistance Design Manual published by the Gypsum Association, or other reference guides.

ill. 17 shows a typical two-hour rated steel column encased in gypsum wallboard.

Spray-applied fire-resistive coatings are typically applied to structural steel framing during the construction of a building and are seldom specified by the interior designer. However, if such fireproo fing is removed or damaged during interior construction, it must be patched by a qualified worker.

Intumescent materials are commonly used in fire-resistive-rated doors, fire-stopping penetrations through fire-rated walls and floors, and for applied coatings. An intumescent material is one that swells and chars to form a smoke and fire barrier when exposed to heat. Intumescent materials for details may take the form of sealants, gasketing, and coatings. These are generally not specified by the interior designer but may be used in door details where a positive pressure fire-rated door assembly is required. When a door must meet the requirement of positive-pressure fire testing, it must have approved gasketing or intumescent material along its edge or on the frame. The material can be placed in a small dado along the edge of the door or in a reveal in the frame.

Fire-retardant coatings may also be applied to wood panel products, finish paneling, metal, fabrics, and other materials to give then a Class A flame spread rating. However, the available colors and textures may be limited, depending on the product and manufacturer, and may affect the final, finished appearance.

Use Only Tested and Rated Assemblies and Materials

Fire-resistance rated assemblies, such as partitions, doors, and glazing, need to be tested according to industry standards to be approved for use in buildings. E.g., partitions and some glazing systems must meet the requirements of ASTM E119, Standard Test Methods for Fire Tests of Building Construction and Materials and doors must be tested in accordance with NFPA 252, Fire Tests of Door Assemblies. Refer to Tbl. 4 for a summary of fire testing required for various interior components. The interior designer must verify with the manufacturer that a product or assembly meets the requirements of the local building code.

Use Listed or Labeled Components

For individual components, such as electrical devices, lighting fixtures, doors, hardware, and other building products, an independent testing laboratory may be required to verify that the component meets the requirements of a standard. One of the best-known testing laboratories is Underwriters Laboratories (UL). When a product successfully passes the prescribed test, it’s given a UL label. There are several types of UL labels, and each means something different.

When a complete and total product is successfully tested, it receives a listed label. This means that the product passed the safety test and is manufactured under the UL follow-up services program. A classified label means that samples of the product were tested for certain types of uses only. In addition to the classified label, the product must also carry a statement specifying the conditions that were tested for. The detailer should verify that required products, such as electrical devices, are UL listed or labeled or that other approved testing agencies have tested the product.


Not all details must provide acoustical control, but when it’s important the design responses listed in this section may be considered. For interior design, there are three types of conditions that require acoustical control. These are controlling sound within a room, controlling the transmission of sound between spaces, and controlling the transmission of vibration throughout a space or building. For many designs, the interior designer can apply these design responses directly. For critical applications, such as recording studios, concert halls, large lecture halls, and spaces close to unusually loud noise-producing sources (like train tracks or highways), an acoustical consultant should be employed.

Noise Control and Reverberation Controlling sound within a space may either involve trying to minimize unwanted sound (noise) or trying to enhance reflection and reverberation, E.g., in a classroom or concert hall.

There are four detailing responses for noise control.


Removing or controlling the source is the simplest way to control noise within a room.

However, this is not always possible if the noise is created by a fixed piece of machinery outside of the room or normal human activity within the room. If a single piece of machinery is producing the noise, it can often be enclosed or modified to reduce it noise output.


Barrel vaulted hallways or circular rooms produce undesirable focused sounds if they are finished with a hard surface such as gypsum wallboard. Use these shapes carefully and only where the focused sound may not be annoying or disruptive. Alternately, they can be covered with sound-absorbent material. Rooms that focus sound in some places and not others may also deprive some listeners of useful re flections.


A highly re flective surface, such as glass, can reflect a noise-producing source into another area. For point sources, the angle of incidence is equal to the angle of reflection so that this simple geometry can be used to estimate how to orient a finished surface. In other situations, it may be desirable to re flect the sound, as in a lecture or concert hall.


One of the best and most common methods of controlling noise within a space is to add absorptive materials. Sound absorption is used to reduce the intensity level of sound within a space, to control unwanted sound re flections, to improve speech privacy, and to decrease reverberation. A detailed discussion of acoustics and sound absorption is beyond the scope of this guide; however, keep the following points in mind:

++ The absorption of a material is defined by the coe fficient of absorption, a, which is the ratio of the sound intensity absorbed by the material to the total intensity reaching the material. The maximum absorption possible, therefore, is 1, that of free space. Generally, a material with a coe fficient below 0.2 is considered to be re flective and one with a coe fficient above 0.2 is considered sound absorbing. These coe fficients are published in manufacturers' technical literature.

++ The coe fficient of absorption varies with the frequency of the sound, and some materials are better at absorbing some frequencies than others. For critical applications, all frequencies must be checked, but for convenience the single-number noise reduction coe fficient (NRC) is used. The NRC is the average of a material's absorption coe fficients at the four frequencies of 250, 500, 1000, and 2000 Hz, rounded to the nearest multiple of 0.05. Some typical NRC ratings are shown in Tbl. 4. The higher the number, the better the material is in absorbing sound at most frequencies encountered in interior design.

Tbl. 4 Noise Reduction Coe fficients Material NRC Marble or glazed tile 0.00 Gypsum wallboard 0.05 Vinyl tile on concrete 0.05 Heavy glass 0.05 Wood strip flooring 0.10 Plywood paneling 0.15 Carpet, direct glue to concrete 0.30 Carpet, 1/2 in. pile on concrete 0.50 Heavy velour fabric (18 oz.) 0.60 Suspended acoustic tile, 5/8 in. 0.60 Fiberglass wall panel, 1 in. 0.80 Suspended acoustic tile, 1 in. 0.90 Note: These are representative of various materials based on the older NRC ratings. The Sound Absorption Average (SAA) is the current method of rating the average noise reduction of materials over several frequency bands.

Although most product literature still gives NRC ratings, the NRC has been superseded by the sound absorption average (SAA), although both are similar and provide a single number rating. The SAA is the average of the absorption coe fficients for the 12 one-third octave bands from 200 to 2500 Hz when tested in accordance with ASTM C423.

++ The total absorption of a material depends on the material's coe fficient of absorption and area. The unit used for this quantity is called the sabin, which is the absorption value of 1 ft 2 of material with a perfect absorption of 1.0 (An SI sabin equals 10.76 U.S. sabins). The total absorption in a room is the sum of the various individual material absorptions. Finishes and construction detailing should be balanced to provide the best overall room absorption.

++ The average absorption coe fficient of a room should be at least 0.20. An average absorption above 0.50 is usually not desirable, nor is it economically justified. A lower value is suitable for large rooms, while larger values are suitable for small or noisy rooms.

++ Although absorptive materials can be placed anywhere, ceiling treatment for sound absorption is more effective in large rooms, while wall treatment is more effective in small rooms.

++ Generally, absorption increases with an increase in thickness of a porous absorber, except for low-frequency sounds that require special design treatment.

++ The amount of absorption of a porous type of sound absorber, such as fiberglass or mineral wool, depends on (1) material thickness, (2) material density, (3) material porosity, and (4) the orientation of the material's fibers.

Transmission Control

Controlling sound transmission is a different problem than controlling sound within a room.

For interior designers, the most common situation is detailing partitions to control sound, but it may also include detailing ceilings within an existing building to decrease sound transmission between floors.

To simplify the selection of partitions and other building components, such as doors, a single-number rating called the sound transmission class (STC) is often used to rate the transmission loss of construction. The higher the STC rating, the better the barrier is (theoretically) in stopping sound. Tbl. 5 lists some STC ratings, in decibels (dB) and their subjective effects on hearing. Manufacturers' literature, testing laboratories, and reference literature typically give the transmission loss at different frequencies.

STC ratings represent the ideal loss through a barrier under laboratory conditions. Partitions, floors, and other construction components built in the field are seldom constructed as well as those in the laboratory. Also, breaks in the barrier such as cracks, electrical outlets, doors, and the like will significantly lessen overall noise reduction. Because of this, a published rating for a barrier should be at least 2 to 3 dB higher than the rating actually wanted.

Tbl. 5 Effect of Barrier STC Ratings on Hearing STC Subjective effect 25 Normal speech can be clearly heard through the barrier.

30 Loud speech can be heard and understood fairly well.

35 Loud speech is not intelligible but can be heard.

42-45 Loud speech can only be faintly heard, and normal speech cannot be heard.

46-50 Loud speech not audible and loud sounds other than speech can only be heard faintly, if at all.

Tbl. 6 Sound Isolation Criteria of Dwelling Units Partition Function between Dwellings STC Ratings, dB Apartment A Apartment B Grade I, Luxury Grade II, Average Grade III, Minimum bedroom The most desirable plan is to have the partition separating spaces with equivalent function; E.g., living room opposite living room.

Whenever a partition wall might serve to separate several functional spaces, the highest criterion must prevail.

Or dining, or family, or recreation room.

Assuming that there is no entrance door leading from corridor to living unit.

If a door is part of the corridor partition, it must have the same rating as the corridor. The most desirable arrangement has the entrance door leading from the corridor to a partially enclosed vestibule or foyer in the living unit.

Double-wall construction is recommended to provide, in addition to airborne sound insulation, isolation from impact noises generated by the placement of articles on pantry shelves or the slamming of cabinet doors.

Special detailing is required for vibration isolation of plumbing in kitchens and bathrooms.

Closets may be used as buffer zones, provided that unlouvered doors are used.

Doors leading to bedrooms and bathrooms preferably should be of solid-core construction and gasketed to ensure a comfortable degree of privacy.

Source: A Guide to Airborne, Impact, and Structure Borne Noise Control in Multifamily Dwellings. U.S. Dept. of Housing and Urban Development, HUD-TS-24 (1974)

Minimum STC ratings are required by the IBC as well as various government agencies for residential construction. Tbl. 6 provides a summary of some common STC requirements.

In critical situations, transmission loss and selection of barriers should be calculated using the values for various frequencies rather than the single STC average value. Some materials may allow an acoustic "hole," stopping most frequencies but allowing transmission of a certain range of frequencies. However, for preliminary design purposes the STC value is adequate.

Although there are several ways to minimize problems with sound transmission, including space planning and controlling the source, there are six detailing responses for noise transmission control.


Because sound energy must be transmitted through a material to be heard in an adjacent space, it must overcome the inertia of the material. The heavier or more massive the material, the less sound transmitted. E.g., a thin piece of glass won’t reduce sound transmission as much as a gypsum wallboard partition. A double layer of wallboard is better than a single layer.


Although the transmission of sound is primarily retarded by the mass of the partition, the stiffness, or rigidity, of the partition is also important. Given two partitions of the same weight per square foot, the one with less stiffness will perform better than the other. Using resilient channels or proprietary products to support one or more layers of gypsum wallboard can reduce partition stiffness. The channels or resilient products " float" the wallboard to dampen sound striking it rather than allowing it to be transmitted to the stud and then through the partition.


As sound energy is transmitted through one layer of material into a partition or ceiling cavity, it sets the air in motion, which, in turn, causes the second layer to vibrate, transmitting the sound energy. By placing absorbing material in the cavity this energy is further reduced. This is most often done with acoustic insulation or simple fiberglass insulation. In ceiling plenums, acoustical batts can be placed on top of the suspended ceiling tiles.

ill. 18 shows the combined use of the three design responses discussed above.

ill. 18 Sound attenuation partition components double-layer gypsum wallboard insulation in cavity resilient channel single-layer gypsum wallboard

ill. 19 Acoustical principles for doors all cracks sealed frame filled with insulation or fully grouted automatic door bottom jamb seal acoustic partition as required, see Fig. 3.18 hard surfaced floor


In addition to the construction of the barrier itself, other variables are critical to the control of sound transmission. Gaps in the barrier must be sealed. Edges at the floor, ceiling, and intersecting walls must be caulked. Penetrations of the barrier should be avoided, but if absolutely necessary, they should be sealed as well. E.g., electrical outlets should not be placed back to back but should be staggered in separate stud spaces and caulked.

Pipes, ducts, and similar penetrations provide a path for both airborne sound and mechanical vibration and should not be rigidly connected to the barrier. Any gaps between ducts, pipes, and a partition should be sealed.

Typical openings, such as doors and glazed openings, must be detailed to seal around the edges and prevent rigid connections. ill. 19 shows one type of acoustical seal around a door opening.

Interior-glazed openings require a combination of approaches to minimize sound trans mission. First, the glazing should be set in resilient gaskets to minimize movement between the glazing and the frame. Second, laminated glass should be used to provide additional mass as well as the damping effect created by the plastic interlayer. If a higher STC rating is needed, a double-glazing system can be used as shown in ill. 20.

ill. 20 Glazing detail for acoustical control laminated glass with air space between two different glass thicknesses pack frame gaps with insulation or caulk acoustic partition neoprene edge seal

ill. 21 Plenum sound barriers (a) suspended wallboard separation (b) lead sheet separation acoustic partition acoustic partition seal penetrations with acoustical sealant 5/8" (16) gypsum wallboard on metal studs suspended from floor above 2-lb. lead sheet attached to deck above with continuous metal anchor, seal vertical joints and penetrations compressible foam tape compressible foam tape pack gap tightly with acoustical insulation lay loose in ceiling


One of the most common problems in o ffices and other commercial construction is the transmission of sound from one space to another in the ceiling plenum if partitions are terminated at the suspended ceiling. The best way to avoid this is to carry partitions from floor to the structural slab above, sealing all penetrations and joints. However, when this

is not possible, plenum barriers should be detailed. Two ways of doing this are shown in ill. 21. With either approach, any penetrations with pipes, ducts, or conduit must be adequately sealed.


Ductwork provides a clear path for sound. Ducts should be lined with sound-absorbent material, and connections between vibrating equipment and the ducts attached to it should not be rigid. If ductwork connects two adjacent rooms, it can be laid out in a Z- or U pattern to increase the length and avoid straight paths for sound. These requirements should be coordinated with the mechanical consultant.

Vibration and Impact Noise Control

In addition to traveling through air, noise can also be transmitted by a source directly through the structure of a building. Dropped objects and footfalls on hard-surfaced floors are a common problem, but machines, HVAC systems, plumbing fixtures, and water flowing through pipes can also create structure-borne noises.

Impact noise, or sound resulting from direct contact of an object with a sound barrier, can occur on any surface, but it generally occurs on a floor and ceiling assembly. It’s usually caused by footfall, shuf fled furniture, and dropped objects.

Impact noise control is quantified by the impact insulation class (IIC) number, a single number rating of a floor/ceiling's impact sound performance. The higher the IIC rating, the better the floor performs in reducing impact sounds in the test frequency range. Minimum ICC ratings are required by the IBC, as well as various government agencies for residential construction. E.g., the IBC requires floor/ceiling assemblies between dwelling units or between a dwelling unit and a public or service area to have a minimum IIC rating of 50 dB (or 45 dB if field tested) when tested in accordance with ASTM E492. Tbl. 7 provides a summary of some common IIC requirements.

The IIC value of a floor can most easily be increased by adding carpet. It can also be improved by providing a resiliently suspended ceiling below, floating a finished floor on resilient pads over the structural floor, or providing sound-absorbing material (insulation) in the air space between the floor and the finished ceiling below.

There are three detailing responses for vibration and impact noise control.

ill. 22 Proprietary acoustic clip approx. 1-1/2" (38) proprietary clip with resilient cushion furring channel gypsum wallboard acoustic insulation, if required.


Flexible connections can be used to isolate noise-producing construction elements. Flexible connectors are available to join ductwork as well as pipes. Rubber or steel spring mounts can be used for machinery. Plumbing pipes can be suspended with wire or attached to the structure with plastic or rubber clamps and hangers to avoid noise caused by expansion and contraction and by the noise of running water.


One of the most effective ways to minimize structure-borne sound is to cushion the source of the noise from the rest of the structure. Using pads on a doorframe is a simple example of this principle. For floors, sound deadening underlayment can be used for hard-surfaced flooring as well as carpeting.

For partitions, one of the most common detailing elements is the resilient channel. An alternate to this is a proprietary device that attaches to the stud and uses a resilient material to hold standard furring channels. Two types are manufactured. The device can be used on metal or wood studs or under a roof or floor structure. The manufacturers claim that the STC rating of a partition using this type of device is better than resilient channels.


If possible, locate mechanical rooms, service areas, and other sources of structure-borne noise together and plan to maximize the distance between them and the areas intended to be quiet.


Whenever water or moisture may be present in or near an interior detail, the designer must take every precaution to prevent moisture intrusion. Moisture can rust unprotected ferrous metal, warp wood, expand absorbent materials, create stains, damage adjacent construction, degrade insulation, and create an environment for mold and mildew. Although resisting moisture intrusion in many interior details is not as di fficult as preventing it in the exterior envelope of a building, it’s no less important.

There are six detailing responses for control of moisture and water resistance.

Use Nonabsorbent Materials

When moisture may be present, the detail should not have any absorbent materials, such as unprotected wood, or fabrics not designed to repel water. Wood may be covered with a waterproof material, painted, or otherwise sealed, but this can create a maintenance problem if exposed. Even countertops covered with plastic laminate may be damaged if water seeps behind the laminate.

Use Nonferrous Metals

Unprotected steel will rust in the presence of moisture. Structural supports, fasteners, or other ferrous components should be avoided if water intrusion is expected in the detail. If steel is used it should be stainless steel, galvanized, or given some other protective coating.

Eliminate or Minimize Joints One of the easiest ways to keep water out of a detail is to minimize the number and location of joints where small cracks may develop, allowing water to seep in. E.g., it’s easy to detail a continuous cove between a countertop and the backsplash instead of using two separate pieces. Joints are better located on vertical services where water is likely to run off instead of on horizontal surfaces where standing water may be a problem. For continuously wet areas, such as shower rooms, reducing the number of joints reduces the likelihood of leaks.

Employ Overlap

Where water will be splashed on two or more separate pieces of material on vertical or sloped surfaces, they should be lapped like the shingles on a roof instead of being connected with a butt joint. Even if small cracks develop, the shingle effect will prevent water from running behind the finish material.

Use Drips

As with overlaps, drips use gravity to force water to drop away from a construction element instead of running back into the construction by capillary action or surface tension. A drip is simply a groove or sharp edge under a material that forces water flowing vertically down the side of a material to drip away instead of running horizontally back to the main structure. Drips are commonly used on architectural elements, such as the lowest course of lap siding, under windowsills, and at building overhangs. They can also be used on interior details where large quantities of water may be present, such as in commercial washrooms, showers, pools, kitchens, and the like.

ill. 23 Drips to shed moisture without drip groove drip angle drip

ill. 24 Movement joint with thin-set tile saw-cut control joint sealant backer rod controlled crack

Tbl. 8 Recommended Ceramic Tile Expansion Joint Width and Spacing Interior Ceramic Mosaic and Glazed Wall Tile Quarry and Paver tile Exposed to Direct Sunlight or Moisture Spacing, ft. (m) 20-25 (6.10-7.62) 20-25 (6.10-7.62) 8-12 (2.59-3.66) Width, in. (mm) 1/8-1/4a (3-6) 1/4b (6) 1/4 (6)

Use the Correct Sealant and Joint Design

Sealants are commonly used to close small joints where water may be present. They may also allow minor movement of the joint while maintaining a seal. In interior construction, there are two types of joints: non-movement joints and movement joints. Non-movement joints are those where the two adjacent materials are not expected to move relative to each other.

An inside joint in a tile shower is an example of a non-movement joint because the tile is rigidly attached to the backup walls, which won’t move during the life of the installation.

Non-movement joints in wet areas can usually be sealed with an acrylic or silicone sealant.

Movement joints are those designed to accommodate expected movement because of expansion and contraction of materials, movement of the building, or movement of individual parts of the building. E.g., movement joints are required for ceramic tile floors where there are control joints in the concrete floor or where there are large expanses of tile flooring.

See ill. 24.

Verify the required joint size and location with the manufacturer of the material. The recommended joint widths and sizes for ceramic tile are shown in Tbl. 8.

Movement joints in wet interior areas are usually sealed with a silicone sealant, which has good movement capabilities and is impervious to water.

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