7
INTERIOR FINISHES FOR WOOD LIGHT FRAME CONSTRUCTION
• Completing the Building Enclosure
Insulating the Building Frame
Increasing Levels of Thermal Insulation
Radiant Barriers
Vapor Retarders
Air Barriers
Air Infiltration and Ventilation
• Wall and Ceiling Finish
• Millwork and Finish Carpentry
PROPORTIONING FIREPLACES
Interior Doors
Window Casings and Baseboards
Cabinets
Finish Stairs
Miscellaneous Finish Carpentry
PROPORTIONING STAIRS
• Flooring and Ceramic Tile Work
• Finishing Touches
Architect Michael Craig Moore uses a rich palette of stone and wood for floors and millwork contrasting elegantly with light-colored walls and ceiling surfaces. In the foreground is slate flooring. Stairs and wood floors are heartwood only pine (“heart pine”). Wood cabinets and trim are vertical grain Douglas Fir. Cabinet counters and the window seat top (middleground of the image) are a composite sheet material made from compressed paper and phenolic resin. Cabinet pulls are bronze. The exposed structural wood column, to the right in the image, is also Douglas Fir. All wood surfaces are finished with clear polyurethane. Walls and ceilings are covered with standard gypsum wallboard finished with latex primer and top coats. (Photograph by Michael Craig Moore, AIA)
As the exterior roofing and siding of a platform frame building approach completion, the framing carpenters and roofers are joined by workers from a number of other building trades. Masons commence work on fireplaces and chimneys (Figures 7.1 and 7.2). Plumbers begin roughing in their piping (“roughing in” refers to the process of installing the components of a system that will not be visible in the finished building). First to be installed are the large DWV (drain–waste–vent) pipes, which drain by gravity and must therefore have first choice of space in the building; then the small supply pipes, which bring hot and cold water to the fixtures; and the gas piping (Figures 7.3–7.6). If the building will have central warm air heating and/or air conditioning, sheet metal workers install the furnace and ductwork (Figures 7.7–7.9). If the building is to have a hydronic (forced hot water) heating system, the plumbers put in the boiler and rough in the heating pipes and convectors at this time (Figure 7.10). A special variety of hydronic heating is the radiant heating system that warms the floors of the building by means of plastic piping, built into the floors, through which hot water is circulated (Figure 7.11). The electricians are usually the last of the mechanical and electrical trades to complete their roughing in because their wires are flexible and can generally be routed around the pipes and ducts without difficulty (Figure 7.12). When the plumbers, sheet metal workers, and electricians have completed their rough work, which consists of everything except installing the plumbing fixtures, electrical outlets, and air registers and grills, inspectors from the local building department check each of the systems for compliance with the plumbing, electrical, and mechanical codes, as well as to ensure that framing has not been damaged during the installation of these other components.
Once these inspections have been passed, connections are made to external sources of water, gas, electricity, and communications services, and to a means of sewage disposal, either a sewer main or a septic tank and leaching field. Thermal insulation and a vapor retarder are added to the exterior ceilings and walls.
Now a new phase of construction begins, the interior finishing operations, during which the inside of the building undergoes a succession of radical transformations. The elaborate tangle of framing members, ducts, pipes, wires, and insulation rapidly disappears behind the finish wall and ceiling materials. The interior millwork—doors, finish stairs, railings, cabinets, shelves, closet interiors, and door and window casings—is installed. The finish flooring materials are installed as late in the process as possible to save them from damage by the passing armies of workers, and carpenters follow behind the flooring installers to add the baseboards that cover the last of the rough edges in the construction.
FIGURE 7.1 Insulated metal flue systems are often more economical than masonry chimneys (shown here) for furnaces, boilers, water heaters, package fireplaces, and solid-fuel stoves. (Photo courtesy of Selkirk Metalbestos)
Finally, the building hosts the painters who prime, paint, stain, varnish, and paper its interior surfaces. The plumbers, electricians, and sheet metal workers make brief return appearances on the heels of the painters to install the plumbing fixtures; the electrical receptacles, switches, and lighting fixtures; and the air grills and registers. At last, following a final round of inspections and a last-minute round of repairs and corrections to remedy lingering defects, the building is ready for occupancy.
FIGURE 7.2 A mason adds a section of clay flue liner to a chimney. The large flue is for a fireplace, and the three smaller flues are for a furnace and two wood-burning stoves. (Photo by Edward Allen)
FIGURE 7.3 A typical residential wastewater system. All fixtures drain to the building drain through sloping or vertical branch lines. The waste pipe is vented to the exterior at each fixture through a network of vent pipes, shown with broken lines.
FIGURE 7.4 A typical residential water supply system. Water enters the house through a buried line and branches into two parallel sets of distribution lines. One is for cold water. The other passes through the water heater and supplies hot water.
FIGURE 7.5 At the basement ceiling, the plumber installs the plastic waste pipes first to be sure that they are properly sloped to drain. The copper supply pipes for hot and cold water are installed next. (Photo by Edward Allen)
FIGURE 7.6 The plumber's work is easier and less expensive if the building is designed to easily accommodate piping. The “stacked” arrangement shown here, in which a second-floor bathroom and a back-to-back kitchen and bath on the first floor share the same vertical runs of pipe, is economical and easy to rough in, compared with plumbing that does not align vertically from one floor to the next. The double wall framing on the second floor allows plenty of space for the waste, vent, and supply pipes. The second-floor joists are located to provide a slot through which the pipes can pass at the base of the double wall, and the joists beneath the water closet (toilet) are headed off to house its waste pipe. The first floor shows an alternative type of wall framing using a single layer of deeper studs, which must be drilled to permit horizontal runs of pipe to pass through.
FIGURE 7.7 A forced-air system in a two-story building with a basement. The furnace is in the basement. It burns gas or oil, or uses electric resistance heating to warm a heat exchanger that creates warm air. It blows the warm air through sheet metal supply ducts to registers in the floor near the exterior walls. The air returns to the furnace through a centrally located return air duct that has a return air grill near the ceiling of each floor. With the addition of a heat pump or air conditioner, this system can deliver cool, dehumidified air during the warm months.
FIGURE 7.8 The installation of this hot air furnace and air conditioning unit is almost complete, needing only electrical connections. The metal pipe running diagonally to the left carries the exhaust gases from the oil burner to the masonry chimney. The ductwork is insulated to prevent moisture from condensing on it during the cooling season and to prevent excessive losses of energy from the ducts. (Photo by Edward Allen)
FIGURE 7.9 Ductwork and electrical wiring are installed conveniently through the openings in these floor trusses, making it easy to apply a finish ceiling if desired. The 2 × 6 that runs through the trusses in the center of the photograph is a bridging member that restrains the trusses from buckling. (Courtesy of Trus Joist Corporation)
FIGURE 7.10 A hydronic heating system. The boiler burns gas or oil, or uses electric resistance heating to heat water. Pumps circulate the water through pipes that lead to convectors in various zones of the building. Inside each convector, a pipe heats closely spaced metal fins that warm the air in the room. The sheet metal convector covers are shown schematically and have been cut away in this drawing to reveal the metal fins.
FIGURE 7.11 The radiant heating system in this two-story building delivers heat through hydronic tubes that warm the floors. There are four zones, two upstairs and two downstairs. Water is heated in a boiler and pumped through a supply manifold, where thermostatically controlled valves control the water flow to each of the zones.
FIGURE 7.12 The electrician begins work by nailing plastic fixture boxes to the framing of the building in the locations shown on the electrical plan. Then holes are drilled through the framing, and the plastic-sheathed cable, which houses two insulated copper conductors and an uninsulated ground wire, is pulled through the holes and into the boxes, where it is held by insulated staples driven into the wood. After the interior wall materials are in place, the electrician returns to connect outlets, lighting fixtures, and switches to the wires and the boxes and to affix cover plates to finish the installation. (Photo by Edward Allen)
COMPLETING THE BUILDING ENCLOSURE
The walls, roofs, and other surfaces of a building that separate the indoors from the outdoors may be referred to as the thermal envelope, building envelope, or building enclosure. The building enclosure controls the flow of heat, air, and moisture between the interior and exterior of the building. Well-designed and carefully constructed enclosure assemblies help keep a building cooler in summer and warmer in winter by retarding the passage of heat through the exterior surfaces of the building. They help keep the occupants of the building more comfortable by moderating the temperatures of the interior surfaces of the building and reducing convective drafts. They reduce the energy consumption of the building for heating and cooling to a fraction of what it otherwise would be. And they prevent the harmful accumulation of condensation within the exterior walls, roof, and other enclosure assemblies of the building.
Insulating the Building Frame
Thermal insulating materials resist the conduction of heat. Thermal insulation is added to virtually all buildings to limit winter heat loss and reduce summer cooling loads. A material's resistance to the conduction of heat is measured as thermal resistance, abbreviated as R-value, or, in metric units, as RSI-value (or in many cases, also simply as R-value). A material with a higher R-value is a better insulator than one with a lower R-value. Figure 7.13 lists the most important types of thermal insulating materials used in wood light frame buildings and gives some of their characteristics. Glass fiber batts are the most popular type of insulation for use in wood light frame construction, but all of the materials listed find use. Examples of the installation of some of these materials are shown in Figures 6.30, and 7.14–7.16. For a more in-depth discussion of the role of thermal insulation in buildings, see pages 658–662.
FIGURE 7.13 Thermal insulation materials commonly used in light frame wood buildings. The R-values offer a direct means of comparing the relative effectiveness of the different types. For more information on rigid insulation boards commonly used with low-slope, see Figure 16.10.
FIGURE 7.14 (a) Installing a polyethylene vapor retarder over glass fiber batt insulation using a staple hammer, which drives a staple each time it strikes a solid surface. The batts are unfaced and stay in place between the studs by friction. (b) Stapling faced batts between roof trusses. The R-value of the insulation is printed on the facing. (c) Placing unfaced batts between ceiling joists in an existing attic. Vent spacers should be used at the eaves (see Figure 6.6). (d) Working from below to insulate a floor over a crawlspace. Batts in this type of installation are usually retained in place by pieces of stiff wire cut slightly longer than the distance between joists and sprung into place at frequent intervals below the insulation. (e) Insulating crawlspace walls with batts of insulation suspended from the sill. The header space between the joist ends has already been insulated. (See also Figure 5.8.) (Courtesy of Owens-Corning Fiberglas Corporation)
FIGURE 7.15 (a) Spraying a low-density polyicynene foam insulation between studs of a wood light frame building. At the time of spraying, the components are dense liquids, but they react immediately with one another to produce a low-density foam, as has already occurred at the bottom of the cavity. The foam in the cavity to the right has already been trimmed off flush with the studs. (b) Trimming off excess foam with a special power saw. (Courtesy of Icynene, Inc., Toronto, Canada)
Increasing Levels of Thermal Insulation
A wall framed with 2 × 4 (38 × 89 mm) studs and filled with glass fiber batt insulation can achieve a thermal resistance of approximately R-13 to R-15 (RSI-90 to 104). According to current North American energy code standards, this is adequate for a residential building in the southern portions of the United States and Hawaii but is insufficient for colder regions. To achieve a higher insulation value, the designer may either increase the thickness of the insulation or use an insulation material that has a higher R-value for an equal thickness. Figure 7.17 shows two commonly employed solutions, either of which achieves an insulation value of R-19 (RSI-132) or greater. Figure 7.20 illustrates two possible approaches to achieving even higher insulation levels in walls. Spray foam and rigid foam insulation materials can also be used, taking advantage of the relatively high R-value per thickness of these materials, and in the case of spray foam, its ability to also reduce air leakage.
FIGURE 7.16 Blowing loose-fill glass fiber insulation into a ceiling below an attic. A vapor retarder was installed on the bottom side of the joists and then a gypsum board ceiling, which supports the insulation. Vent spacers were installed at the eaves to prevent the insulation from blocking eave vents. (Courtesy of Owens-Corning Fiberglas Corporation)
Figures 7.18 and 7.19 illustrate methods for reducing thermal bridging at corners and at headers over doors and windows. Thermal bridging occurs where solid framing members interrupt the thermal insulation layer, creating wall areas with a lower thermal resistance than surrounding areas and reducing the insulation efficiency of the wall as a whole. Use of advanced framing techniques (Figure 5.64) or insulating sheathing (Figure 7.17, right) are examples of other approaches to reducing thermal bridging in wall framing.
The insulation level can also be reduced where ceiling insulation under a sloped roof must be compressed somewhat in the diminishing space between the roof sheathing and the top of the exterior wall. This can be observed in Figures 7.17 and 7.20. A raised-heel roof truss (Figure 7.21) is one way to overcome this problem.
FIGURE 7.17 Insulation levels in walls of light frame buildings can be increased from the R13 to R-15 (RSI-90 to RSI-104) of a 2 × 4 stud wall to R19 (RSI-132) or more by using either 2 × 6 framing and thicker batt insulation (left) or 2 × 4 framing with plastic foam sheathing in combination with batt insulation (right). The foam sheathing insulates the wood framing members as well as the cavities between them but can complicate the process of installing some types of siding.
FIGURE 7.18 Window and door headers in 2 × 6 framing require special detailing. Two alternative header details are shown here in section view: (a) The header members are installed flush with the interior and exterior surfaces of the studs, with an insulated space between. This detail is thermally efficient but may not provide sufficient nailing for interior finish materials around the window. (b) A 3 × 2 spacer provides full nailing around the opening.
FIGURE 7.19 Two alternative corner post details for 2 × 6 stud walls, shown in plan view: (a) Each wall frame ends with a full 2 × 6 stud, and a 2 × 4 nailer is added to accept fasteners from the interior wall finish. (b) For maximum thermal efficiency, one wall frame ends with a 2 × 4 stud flush with the interior surface, which eliminates any thermal bridging through studs.
FIGURE 7.20 With the two framing methods shown here, walls can be insulated to any desired level of thermal resistance.
FIGURE 7.21 A raised-heel roof truss provides plenty of space for attic insulation at the eave.
Radiant Barriers
In warmer regions, radiant barriers may be used in roofs and walls to reduce the flow of solar heat into the building. These are thin sheets or panels faced with a bright metal foil that blocks the transmission of infrared (heat) radiation. Most types of radiant barriers are made to be installed over the rafters or studs and beneath the sheathing, so they must be put in place during the framing of the building. They are effective only if the bright surface of the barrier faces a ventilated airspace; this allows the reflective surface to work properly and provides for the convective removal of solar heat that has passed through the outer skin of the building. Some radiant barrier panels are configured with folds that provide this airspace automatically. Radiant barriers are used in combination with conventional insulating materials to achieve the desired overall thermal performance.
Vapor Retarders
A vapor retarder (often called, less accurately, a vapor barrier) is a membrane of metal foil, plastic, treated paper, or primer paint placed on the warm side of thermal insulation to prevent water vapor from entering the insulation and condensing into liquid. The function of a vapor retarder is explained in detail on pages 658–661. Its role increases in importance in colder climates, as thermal insulation levels increase, and for interior spaces such as pools or spas with high humidity levels.
Many batt insulation materials are furnished with a vapor retarder layer of treated paper or aluminum foil already attached. Most designers and builders in cold climates, however, prefer to use unfaced insulating batts and to apply a separate vapor retarder of polyethylene sheet, because a vapor retarder attached to batts has a seam at each stud that can leak significant quantities of air and vapor, while the separately applied sheet has fewer seams.
Air Barriers
Air barriers control the leakage of air through the building enclosure. They significantly reduce building energy consumption and help protect enclosure assemblies from moisture condensation by restricting the infiltration of humid air. The role of the air barrier in the building enclosure is discussed in more detail on pages 800–803.
Housewraps applied over exterior sheathing, discussed on page 222, are a common way to incorporate an air barrier into wood light frame buildings. Or, when plastic sheeting used as a vapor retarder is carefully sealed against air leakage, it too can function as an air barrier. Another method, called the airtight drywall approach (ADA), relies on the gypsum board (drywall) panels used to finish interior walls and ceilings to create the air barrier. In this method, meticulous attention is given to sealing joints between these panels and framing members so as to create a continuous air-impermeable boundary around interior conditioned spaces (Figure 7.22). The ADA requires careful attention to details of construction: Potential air leakage paths around the edges of gypsum panels and between abutting framing members must be sealed with compressible foam tape gaskets or joint sealants during the installation of these members; gypsum board is applied to all the interior surfaces of the outside walls before the interior partitions are framed, eliminating potential air leaks where these interior partitions join the outside walls; and gaskets, sealants, or special airtight boxes are used to seal air leakage paths around electrical fixtures and other penetrations.
FIGURE 7.22 An air barrier system must form a continuous airtight boundary between the inside and outside of the building. In the ADA, the air barrier system is constructed of gypsum wallboard, wood framing members, and the concrete foundation wall (the shaded elements in the figure). Tapes and caulks (see the enlarged inset) are used to seal leakage paths between these components.
The ADA requires careful attention to joint sealing during the construction of the building frame and the installation of drywall. A related system, called simple caulk and seal, relies on the strategic application of joint sealants after framing and drywalling are complete to achieve much the same result as the ADA. Simple caulk and seal is easier to coordinate, because the joint sealing occurs separately from the work of other trades. However, it may be less successful at eliminating air leakage paths that become concealed and inaccessible before the sealing work takes place.
The increased concern for controlling air leakage through the building enclosure has also led to higher standards of window and door construction and greater care in sealing around exterior electrical outlets and other penetrations of the exterior wall.
Air Infiltration and Ventilation
Reducing the flow of heat and air through the building enclosure reduces energy consumption. However, tightly constructed homes or apartment buildings may exchange so little air with the outdoors that if they are not adequately ventilated, indoor moisture, odors, and chemical pollutants can build up to intolerable or unhealthful levels. Opening a window to ventilate the dwelling is one way to introduce fresh air, but during heating or cooling seasons this wastes fuel. A better solution is a mechanical ventilation system designed to supply fresh air to interior spaces at a controlled and consistent rate. Such a ventilation system may be integrated with a forced-air heating or cooling system or it may be dedicated solely to satisfying ventilation needs. For greater energy efficiency, an air-to-air heat exchanger—a device that recovers most of the heat from the air exhausted from the building and adds it to the outside air that is drawn in—may be part of such a system. Nonresidential buildings of wood light frame construction generally require higher rates of ventilation than residential structures, and here, too, low-infiltration construction and appropriately designed ventilation systems are important to maintaining a healthful and comfortable interior environment while also reducing heating and cooling costs.
WALL AND CEILING FINISH
Gypsum-based plaster and drywall finishes have always been the most popular for walls and ceilings in wood frame buildings. Their advantages include substantially lower installed costs than any other types of finishes, adaptability to either painting or wallpapering, and, importantly, a degree of fire resistance that offers considerable protection to a combustible frame. Three-coat gypsum plaster applied to wood strip lath was the prevalent wall and ceiling finish system until the Second World War, when gypsum board (also called drywall) came into increasing use because of its lower material cost, more rapid installation, and utilization of less skilled labor. More recently, veneer plaster systems have been developed that offer surfaces of a quality and durability superior to those of gypsum board, often at comparable prices.
Plaster, veneer plaster, and gypsum board finishes are presented in detail in Chapter 23. Gypsum board remains the favored material for small builders who do all the interior finish work in a building themselves because the skills and tools it requires are largely those of carpenters rather than plasterers. In geographic areas where there are plenty of skilled plasterers, veneer plaster captures a substantial share of the market. Almost everywhere in North America, there are subcontractors who specialize in gypsum board installation and finishing and who are able to finish the interior surfaces of larger projects, such as apartment buildings, retail stores, and rental office buildings, as well as individual houses, at highly competitive prices.
In most small buildings, all wall and ceiling surfaces are covered with plaster or gypsum board. Even wood paneling should be applied over a gypsum board backup layer for increased fire resistance. In buildings that require fire walls between dwelling units or fire separation walls between areas with different uses, a gypsum board wall of the required degree of fire resistance can be installed, eliminating the need to employ masons to put up a wall of brick or concrete masonry (Figures 5.67 and 5.68).
MILLWORK AND FINISH CARPENTRY
Millwork (so named because it is manufactured in a planing and molding mill) includes all the wood interior finish components of a building. Millwork is generally produced from much higher-quality wood than that used for framing: The softwoods used are those with fine, uniform grain structure and few defects, such as Sugar pine and Ponderosa pine. Flooring, stair treads, and millwork intended for transparent finish coatings such as varnish or shellac are customarily made of hardwoods such as Red and White oak, Cherry, Mahogany, or Walnut, or of similar quality hardwood plywoods.
Moldings are also produced from high-density plastic foams, parallel strand lumber, and medium-density fiberboard as a way of reducing costs and minimizing moisture expansion and contraction. All these materials must be painted.
The quality of millwork is regulated by the Architectural Woodwork Institute (AWI), which defines three grades: Economy, Custom, and Premium. Economy Grade cabinetry and millwork represents the minimum expectation of quality. Custom Grade provides a well-defined degree of control over the quality of materials, workmanship, and installation and is the grade to which most cabinets are built. Premium Grade is the most expensive, and is reserved for the very finest cabinets and millwork.
Ever since fireplaces were first developed in the Middle Ages, people have sought formulas for their construction to ensure that the smoke from a fire would go up the chimney and the heat into the room, rather than the reverse, which is too often the case. To this day, there is little scientific information on how fireplaces work and how to design them. What we do have are some measurements taken from fireplaces that seem to work reasonably well. These have been correlated and arranged into a table of dimensions (Figures B and C) that enables designers to reproduce the critical features of these fireplaces as closely as possible.
Several general principles are clear: The chimney should be as tall as possible. The cross-sectional area of the flue should be about one-tenth the area of the front opening of the fireplace. A damper should be installed to close off the chimney when no fire is burning and to regulate the passage of air through the firebox when the fire is burning (Figure A). A smoke shelf above the damper reduces fireplace malfunctions caused by cold downdrafts in the chimney. Splayed sides and a sloping back in the firebox reduce smoking and throw more heat into the room.
Starting from these general principles, two schools of thought have developed concerning how a fireplace should be shaped and proportioned. Most fireplaces in North America are built to the conventional standards that are tabulated here. Many designers, however, favor the rules for fireplace construction that were formulated by Count Rumford in the 1790s. These produce a fireplace with a taller opening and a shallower firebox than the conventional fireplace. The intention of the Rumford design is to attain a higher efficiency by throwing more radiant heat from the fire-warmed bricks at the back of the firebox to the occupants of the building.
Building codes place a number of restrictions on fireplace and chimney construction. Typically, these call for a 2-inch (51-mm) clearance between the wood framing and the masonry of a chimney or fireplace, and clearances to combustible finish materials around the opening of the fireplace as shown in Figure B. Also specified by code are the minimum thicknesses of masonry around the firebox and flue, the minimum size of the flue, the minimum extension of the chimney above the roof, and steel reinforcing for the chimney. A combustion air inlet must be provided to bring air from the outdoors to the base of the fire. For ready reference in proportioning fireplaces, use the values in the accompanying Figures B and C. In most cases, the designer need not detail the internal construction of the fireplace beyond the information given in these dimensions, because masons are well versed in the intricacies of assembling a fireplace.
There are several alternatives to the conventional masonry fireplace. One is a steel or ceramic fireplace liner that takes the place of the firebrick lining, damper, and smoke chamber. Many of these products have internal passages that draw air from the room, warm it with the heat of the fire, and return it to the room. The liner is set onto the underhearth and built into a masonry facing and chimney by the mason.
Another alternative is the “package” fireplace, a self-contained, fully insulated unit that needs no masonry whatsoever. It is usually set directly on the subfloor and fitted with an insulated chimney of prefabricated metal pipe. It may be faced with any desired ceramic or masonry materials. Many package fireplaces are made to burn gas rather than wood.
A third alternative is a freestanding metal stove that burns wood, coal, or other solid fuel. Stoves are available in hundreds of styles and sizes. Their principal advantage is that they provide more heat to the interior of the building per unit of fuel burned than a fireplace. A stove requires a noncombustible hearth and a fire-protected wall that are rather large in extent. The designer should consult the local building code at an early stage of design to be sure that the room is big enough to hold a stove of the desired dimensions.
FIGURE A A cutaway view of a conventional masonry fireplace. Concrete masonry is used wherever it will not show, to reduce labor and material costs, but if hollow concrete blocks are used, they must be filled solid with grout. The damper and ash doors are prefabricated units of cast iron, as is a combustion air inlet in the hearth (not shown here) that connects with a sheet metal duct to an outdoor air intake. The flue liners are made of fired clay and are highly resistant to heat. The flue from the furnace or boiler in the basement slopes as it passes the firebox so as to adjoin the fireplace flue and keep the chimney as small as possible.
FIGURE B The critical dimensions of a conventional masonry fireplace, keyed to the table in Figure C. Dimension D, the depth of the hearth, is commonly required to be 16 inches (405 mm) for fireplaces with openings up to 6 square feet (0.56 m2) and 20 inches (510 mm) if the opening is larger. The side extension of the hearth, E, is usually fixed at 8 inches (200 mm) for smaller fireplace openings and 12 inches (305 mm) for larger ones.
FIGURE C Recommended proportions for conventional masonry fireplaces, based largely on figures given in Ramsey/Sleeper, Architectural Graphic Standards (9th ed.), New York, John Wiley & Sons, Inc., 1994.
Millwork is manufactured and delivered to the building site at a very low moisture content, typically about 10 percent, so it is important to protect it from moisture and high humidity before and during installation to avoid swelling and distortions. The humidity within the building is frequently high at the conclusion of plastering or gypsum board work. The framing lumber, concrete work, masonry mortar, plaster, drywall joint compound, and paint are still diffusing large amounts of excess moisture into the interior air. As much of this moisture as possible should be ventilated to the outdoors before finish carpentry (the installation of millwork) commences. Windows should be left open for a few days, and in cool or damp weather the building's heating system should be turned on to raise the interior air temperature and help drive off excess water. In hot, humid weather, the air conditioning system should be activated to dry the air.
Interior Doors
Figure 7.23 illustrates five doors that fall into three general categories: Z-brace, panel, and flush. Z-brace doors, mostly built on site, are used infrequently because they are subject to distortions and large amounts of moisture expansion and contraction in the broad surface of boards whose grain runs perpendicular to the width of the door. Panel doors were developed centuries ago to minimize dimensional changes and distortions caused by the seasonal changes in the moisture content of the wood. They are widely available in readymade form from millwork dealers. Flush doors are smooth slabs with no surface features except the grain of the wood. They may be either solid core or hollow core. Solid-core doors consist of two veneered faces glued to a solid core of wood blocks or bonded wood chips (Figure 7.24). They are much heavier, stronger, and more resistant to the passage of sound than hollow-core doors and are also more expensive. In residential buildings, their use is usually confined to entrance doors, but they are frequently installed throughout commercial and institutional buildings, where doors are subject to greater abuse. Hollow-core doors have two thin plywood faces separated by an airspace. The airspace is maintained by an interior grid of wood or paperboard spacers to which the veneers are bonded. Flush doors of either type are available in a variety of veneer species, the least expensive of which are intended to be painted.
For speed and economy of installation, most interior doors are furnished prehung, meaning that they have been hinged and fitted to frames at the mill. The carpenter on the site merely tilts the prehung door and frame unit up into the rough opening, plumbs it carefully with a spirit level, shims it with pairs of wood shingle wedges between the finish and rough jambs, and nails it to the studs with finish nails through the jambs (Figure 7.25). Casings are then nailed around the frame on both sides of the partition to close the ragged gap between the door frame and the wall finish (Figure 7.26). To save the labor of applying casings, door units can also be purchased with split jambs that enable the door to be cased at the mill. At the time of installation, each door unit is separated into halves, and the halves are installed from opposite sides of the partition to telescope snugly together before being nailed in place (Figure 7.27).
FIGURE 7.23 Types of wood doors.
FIGURE 7.24 Edge details of three types of wood doors. The panel is loosely fitted to the stiles and rails in a panel door to allow for moisture expansion of the wood. The spacers and edge strips in hollow-core doors have ventilation holes to equalize air pressures inside and outside the door.
FIGURE 7.25 Installing a door frame in a rough opening. The shingle wedges at each nailing point are paired in opposing directions to create a flat, precisely adjustable shim to support the frame.
Window Casings and Baseboards
Windows are cased in much the same manner as doors (Figures 7.28 and 7.29). After the finish flooring is in place, baseboards are installed to cover the gap between the flooring and the wall finish and to protect the wall finish against damage by feet, furniture legs, and cleaning equipment (Figures 7.36K–N and 24.32).
When installing casings or baseboards, the carpenter recesses the heads of finish nails below the surface of the wood, traditionally using a hammer and a nail set (a hardened steel punch), or, as is more likely today, a powered finish nail gun. Later, the painters will fill these nail holes with a paste filler and sand the surface smooth after the filler has dried so that the holes will be invisible in the painted woodwork. For transparent wood finishes, nail holes are usually filled after the finishes have been applied, using wax-based fillers that are supplied in a range of colors to match the full range of wood species.
FIGURE 7.26 Casing a door frame. (a) The heads of the finish nails in the frame are recessed below the surface of the wood with a steel nail set. (b) The top piece of casing, mitered to join the vertical casings, is ready to install, and glue is spread on the edge of the frame. (c) The top casing is nailed into place. (d) The nails are set below the surface of the wood, ready for filling. (Photos by Joseph Iano)
The nails in casings and baseboards must reach through the plaster or gypsum board to penetrate the framing members beneath in order to make a secure attachment. Eight- or ten-penny finish or casing nails are customarily used.
Cabinets
Cabinets for kitchens, bathrooms, bedrooms, workrooms, and other spaces may be either custom- or factory-fabricated. Custom cabinets are fabricated in specialty woodworking shops according to drawings and specifications prepared individually for each project. Like quality millwork, custom cabinets are constructed to AWI specifications, usually Premium or Custom Grade. Less expensive, prefabricated cabinets are factory-manufactured to standard sizes and configurations. Both types of cabinets are usually delivered to the construction site fully finished. In project specifications, custom cabinets are specified as architectural wood casework, and factory-made cabinets are specified as manufactured wood casework.
FIGURE 7.27 A split-jamb interior door arrives on the construction site prehung and precased. The halves of the frame are separated and installed from opposite sides of the partition.
FIGURE 7.28 Casing a window. (a) Marking the length of a casing. (b) Cutting the casing to length with a power miter saw. (c) Nailing the casing. (d) Coping the end of a molded edge of an apron with a coping saw so that the molding profile will terminate neatly at the end of the apron. (e) Planing the edge of the apron, which has been ripped (sawn lengthwise, parallel to the grain of the wood) from wider casing stock. (f) Applying glue to the apron. (g) Nailing the apron, which has been wedged temporarily in position with a stick. (h) The coped end of the apron, in place. (i) The cased window, ready for filling, sanding, and painting. (Photos by Joseph Iano)
On the construction site, cabinets are installed by shimming against wall and floor surfaces as necessary to make them level and screwing through the backs of the cabinet units into the wall studs (Figures 7.30 and 7.31). The tops are then attached with screws driven up from the cabinets beneath. Kitchen and bath countertops are cut out for built-in sinks and lavatories, which are subsequently installed by the plumber.
FIGURE 7.29 Simple but carefully detailed and skillfully crafted window casings in a restaurant. (Woo & Williams, Architects. Photographer: Richard Bonarrigo)
FIGURE 7.30 Prepainted wood kitchen cabinets installed before the installation of shelves, drawers, doors, and countertops. (Photo by Edward Allen)
FIGURE 7.31 Custom-designed cabinets brighten a remodeled kitchen in an older house. (Architects: Dirigo Design. Photo © Lucy Chen)
Finish Stairs
Finish stairs are either constructed in place (Figures 7.32 and 7.33) or shop built (Figures 7.34 and 7.35). Shop-built stairs tend to be more tightly constructed and to squeak less in use, but site-built stairs can be fitted more closely to the walls and are more adaptable to special situations and framing irregularities. Stair treads are usually made of wear-resistant hardwoods such as Oak or Maple. Risers and stringers may be made of any reasonably hard wood, such as Oak, Maple, or Douglas fir.
FIGURE 7.32 Left: stair terminology and clearances for wood frame residential construction. Right: types of stairs. 1. Straight run. 2. L-shaped stair with landing. 3. 180-degree turn with landing. 4. L-shaped stair with winders (triangular treads). Winders are helpful in compressing a stair into a much smaller space but are perilously steep where they converge, and their treads become much too shallow for comfort and safety. Building codes limit their minimum dimensions and restrict their use to within dwelling units. 5. L-shaped stair whose winders have an offset center. The offset center can increase the minimum tread dimension to within legal limits. 6. A spiral stair (in reality a helix, not a spiral) consists entirely of winders and is generally illegal for any use but a secondary stair in a single-family residence. 7. A spiral or circular stair with an open center of sufficient diameter can have its treads dimensioned to legal standards.
FIGURE 7.33 Constructing a finished stair in place. The joint between the riser and the open stringer is a miter. The balusters, posts, and handrail are purchased ready made from millwork suppliers and cut to fit.
FIGURE 7.34 A shop-built stair. All the components are glued firmly together in the shop, and the stair is installed as a single piece.
Three openings are required in stair-cases; the first is the door thro' which one goes up to the stair-case, which the less it is hid to them that enter into the house, so much the more it is to be commended. And it would please me much, if it was in a place, where before that one comes to it, the most beautiful part of the house was seen; because it makes the house (even tho' small) seem very large; but however, let it be manifest, and easily found. The second opening is the windows that are necessary to give light to the steps; they ought to be in the middle, and high, that the light may be spread equally every where alike. The third is the opening thro' which one enters into the floor above; this ought to lead us into ample, beautiful, and adorned places.
Andrea Palladio, The Four Books of Architecture, 1570.
Miscellaneous Finish Carpentry
Finish carpenters install dozens of miscellaneous items in the average building—closet shelves and poles, pantry shelving, bookshelves, wood paneling, chair rails, picture rails, ceiling moldings, mantelpieces, laundry chutes, folding attic stairs, access hatches, door hardware, weatherstripping, doorstops, and bath accessories (towel bars, paperholders, and so on). Many of these items are available ready-made from millwork and hardware suppliers (Figures 7.36 and 7.37), but others have to be crafted by the carpenter.
FIGURE 7.35 (a) A worker completes a highly customized curving stair in a shop. (b) Balusters, newel post, and handrail are finely finished in a historical style. (Courtesy of Staircase & Millwork Co., Alpharetta, GA)
FIGURE 7.36 Some common molding patterns for wood interior trim. A and I are crowns, C is a bed, and D and E are coves. All are used to trim the junction of a ceiling and a wall. F is a quarter-round for general-purpose trimming of inside corners. Moldings G–J are used on walls. G is a picture molding, applied near the top of a wall so that framed pictures can be hung from it at any point on special metal hooks that fit over the rounded portion of the molding. H is a chair rail, installed around dining rooms to protect the walls from damage by the backs of chairs. I is a panel molding and J is a batten, both used in traditional paneled wainscoting. Baseboards (K–N) include three single-piece designs and one traditional design (K) using a separate cap molding and shoe in addition to a piece of S4S stock that is the baseboard itself (see also Figure 24.32). Notice the shallow groove, also called a “relieved back,” in the single-piece baseboards and many other flat moldings on this page. This serves to reduce cupping forces on the piece and makes it easier to install even if it is slightly cupped.
Designs AA–FF are standard casings for doors and windows. GG, HH, and II are handrail stock. MM is representative of a number of sizes of S4S material available to the finish carpenter for miscellaneous uses. NN is lattice stock, also used occasionally for flat trim. OO is square stock, used primarily for balusters. PP represents several available sizes of round stock for balusters, handrails, and closet poles. Wood moldings are furnished in either of two grades: N Grade, for transparent finishes, must be of a single piece. P Grade, for painting, may be finger jointed or edge glued from smaller pieces of wood. P Grade is less expensive because it can be made up of short sections of lower-grade lumber with the defects cut out. Once painted, it is indistinguishable from N Grade. The shapes shown here represent a fraction of the moldings that are generally available from stock. Custom molding patterns can be easily produced because the molding cutters used to produce them can be ground quickly to the desired profiles, working from the architect's drawings.
Building codes ensure the design of safe stairs through a number of dimensional requirements. The limitations for stairs as given in the International Building Code (IBC) are summarized in Figure A. The required width of an exit stairway is also calculated according to the number of occupants served by the stair in accordance with formulas given in the code and may be wider than the minimums indicated in this figure. A stair may also not rise more than 12 feet (3660 mm) between landings. Landings contribute to the safety of a stair by providing a moment's rest to the legs between flights of steps. (Architects also generally avoid designing flights of less than three risers because short flights, especially in public buildings, sometimes go unnoticed, leading to dangerous falls.) The width of the landing must equal the width of the stair. The length of a landing must also equal the width of the stair for stairs up to 48 inches (1219 mm) in width but need not exceed this dimension for wider stairs.
Working within the dimensional limits of the IBC, combinations of tread and riser dimensions that are most comfortable underfoot can be found by using the proportional rule that twice the riser dimension added to the tread dimension should equal 24 to 25 inches (610–635 mm). This formula was derived in France two centuries ago from measurements of actual dimensions of comfortable stairs. Figure B gives an example of how this formula is used in designing a new stair, in this case for a single-family dwelling. Because the IBC does not allow variations greater than ⅜ inch (9.5 mm) between successive treads or risers, the floor-to-floor dimension should be divided equally into risers to an accuracy of 0.01 inch or 1 mm to avoid cumulative errors. The framing square used by carpenters in the United States to lay out stair stringers has a scale of hundredths of an inch, and riser dimensions should be given in these units rather than fractions to achieve the necessary accuracy.
Monumental outdoor stairs, such as those that lead to entrances of public buildings, are designed with lower risers and deeper treads than indoor stairs. Many designers relax the proportions of the 2R + T formula a bit for outdoor stairs, raising the sum to 26 or 27 inches (660 or 685 mm), but it is best to make a full-scale mockup of a section of such a stair to be sure that it is comfortable underfoot.
FIGURE A Dimensional limitations for stairs as established by the IBC.
FIGURE B A sample calculation for proportioning a residential stair.
FIGURE 7.37 Fireplace mantels are available from specialized mills in a number of traditional and contemporary designs. Each mantel is furnished largely assembled but is detailed in such a way that it can easily be adjusted to fit any fireplace within a wide range of sizes. (Courtesy of Mantels of Yesteryear, McCaysville, GA, www.mantelsofyesteryear.com)
FLOORING AND CERAMIC TILE WORK
Before finish flooring can be installed, the subfloor is scraped free of plaster droppings and swept thoroughly. Underlayment panels of C–C Plugged plywood or particleboard (in areas destined for resilient flooring materials and carpeting) are glued and nailed over the subfloor, their joints staggered with those in the subfloor to eliminate weak spots. The thicknesses of the underlayment panels are chosen to make the finished floor surfaces as nearly equal in level as possible at junctions between different flooring materials.
In multistory wood light frame commercial and apartment buildings, a floor underlayment specially formulated of poured gypsum or lightweight concrete is often poured over the subfloor. This has a three-fold function: It provides a smooth, level surface for finish floor materials; it furnishes additional fire resistance to the floor construction; and it reduces the transmission of sound through the floor to the apartment or office below. The gypsum or concrete is formulated with superplasticizer additives that make it virtually self-leveling as it is applied (Figure 7.38). A minimum thickness is ¾ inch (19 mm). Poured underlayments are also used to level floors in older buildings, to add fire and sound resistance to precast concrete floors, and to embed plastic tubing or electric resistance wires for in-floor radiant heat.
Floor finishing operations require cleanliness and freedom from traffic, so members of other trades are banished from the area as the flooring materials are applied. Hardwood flooring is sanded level and smooth after installation, then vacuumed to remove the sanding dust. The finish coatings are applied in as dust-free an atmosphere as possible to avoid embedded specks. Resilient-flooring installers vacuum the underlayment meticulously so that particles of dirt will not become trapped beneath the thin flooring and cause bumps in the surface. The finished floors are often covered with sheets of heavy paper or plastic to protect them during the final few days of construction activity. Carpet installation is less sensitive to dust, and the installed carpets are less prone to damage than hardwood and resilient floorings, but temporary coverings are applied as necessary to protect the carpet from paint spills and water stains.
The application of ceramic tile to a portland cement plaster base coat over metal lath for a shower stall is illustrated in Figure 7.39, and finished ceramic tile work is shown in Figure 7.40. Cementitious backer board may be used as a less costly substitute for a cement plaster base coat (Figure 24.29). Wood flooring installation is depicted in Figures 24.32 and 24.33. A finished hardwood floor is shown in Figures 7.41 and 24.34. The installation of ceramic tile and finish flooring materials is covered in more detail in Chapters 23 and 24.
FIGURE 7.38 Workers apply a gypsum underlayment to an office floor. The gypsum is pumped through a hose and distributed with a straightedge tool. Because the gypsum seals against the bottoms of the interior partitions, it can also help reduce sound transmission from one room to another. (© Gyp-Crete Corporation, Hamel, Minnesota)
FIGURE 7.39 Installing sheets of ceramic tile in a shower stall. The base coat of portland cement plaster over metal lath has already been installed. Now the tilesetter applies a thin coat of tile adhesive to the base coat with a trowel and presses a sheet of tiles into it, taking care to align the tiles individually around the edges. A day or two later, after the adhesive has hardened sufficiently, the joints will be grouted to complete the installation. (Photos by Joseph Ianor)
FIGURE 7.40 Ceramic tile is used for the floor, countertops, and backsplash in this kitchen. The border was made by selectively substituting tiles of four different colors for the white tiles used for the field of the floor. (Designer: Kevin Cordes. Courtesy of American Olean Tile)
FIGURE 7.41 Varnished oak flooring, millwork, and casework. (Woo & Williams, Architects. Photographer: Richard Bonarrigo)
FINISHING TOUCHES
When flooring and painting are finished, the plumbers install and activate the lavatories, water closets, tubs, sinks, and shower fixtures. Gas lines are connected to appliances and the main gas valve is opened. The electricians connect the wiring for the heating and air conditioning equipment and (if electric) water heater; mount the receptacles, switches, and lighting fixtures; and put metal or plastic cover plates on the switches and receptacles. The electrical circuits are energized and checked to be sure that they work. The smoke alarms and heat alarms, required by most codes in residential structures, are also connected and tested by the electricians, along with any communications, entertainment, and security system wiring. The heating and air conditioning system is completed with the installation of air grills and registers, or with the mounting of metal convector covers, then turned on and tested. Painted surfaces that have been scuffed or marred are touched up, and last-minute problems are identified and corrected through cooperative effort by the contractors, the owner of the building, and the architect. The building inspector is called in for a final inspection and issuance of an occupancy permit. After a thorough cleaning, the building is ready for use.
SELECTED REFERENCES
1. Lstiburek, Joseph. Builder's Guide to Cold Climates. Westford, MA, Building Science Corporation, 2006.
This guide, along with companion guides for other major climate zones, explains the roles of insulation, vapor retarders, and air barriers in the performance of the building enclosure, and provides guidelines for the construction of energy-efficient and weather-resistant home.
2. Thallon, Rob. Graphic Guide to Interior Details: For Builders and Designers. Newtown, CT, Taunton Press, 2004.
Profusely illustrated, clearly written, and encyclopedic in scope, this book offers complete guidance on interior finishing of wood light frame buildings.
3. Dietz, Albert G. H. Dwelling House Construction (5th ed.). Cambridge, MA, MIT Press, 1990.
This classic text has extensive chapters with clear illustrations concerning chimneys and fireplaces, insulation, wallboard, lath and plaster, and interior finish carpentry.
4. Architectural Woodwork Institute. AWI Quality Standards Illustrated. Reston, VA, updated regularly.
Every detail of every grade of interior woodwork and cabinetry is illustrated and described in this thick volume.
WEB SITES
Interior Finishes for Wood Light Frame Construction
Author's supplementary web site: www.ianosbackfill.com/07_interior_finishes_for_wood_light_frame_construction
Thermal Insulation and Vapor Retarder
Building Science Corporation: www.buildingscience.com
Dow Chemical rigid foam insulation: www.dow.com/styrofoam
Gypsum Association: www.gypsum.org
Icynene Corporation spray-foam insulation: www.icynene.com
Owens Corning insulation products: www.owenscorning.com
Wall and Ceiling Finish
USG gypsum products: www.usg.com
Millwork and Finish
Architectural Woodwork Institute: www.awinet.org
Hardwood Plywood & Veneer Association: www.hpva.org
Jeld-Wen Windows & Doors: www.jeld-wen.com
Window and Door Manufacturers Association: www.wdma.org
Proportioning Fireplaces
Buckley Rumford Company: www.rumford.com
Flooring and Ceramic Tile Work
American Olean Tile: www.americanolean.com
Tile Council of America: www.tileusa.com
KEY TERMS AND CONCEPTS
REVIEW QUESTIONS
1. List the sequence of operations required to complete the interior of a wood light frame building and explain the logic of the order in which these operations occur.
2. What are some alternative ways of insulating the walls of a wood light frame building to R-values beyond the range normally possible with ordinary 2 × 4 (38 × 89 mm) studs?
3. Why are plaster and gypsum board so popular as interior wall finishes in wood frame buildings? List as many reasons as possible.
4. What is the level of humidity in a building at the time installation of the interior wall finishes is completed? Why? What should be done about this and why?
5. Summarize the most important things to keep in mind when designing a stair.
EXERCISES
1. Design and detail a fireplace for a building that you are designing, using the information provided on page 276 to work out the exact dimensions and the information in Chapter 8 to help in detailing the masonry.
2. Design and detail a stairway for a building that you are designing, using the in formation provided on pages 288 and 289 to calculate the dimensions.
3. Visit a wood frame building that you admire. Make a list of the interior finish materials and components, including finishes and species of wood where possible. How does each material and component contribute to the overall feeling of the building? How do they relate to one another?
4. Make measured drawings of millwork details in an older building that you admire. Analyze each detail to discover its logic. What woods were used and how were they sawn? How were they finished?