concrete or concrete-block foundation wall 2 in. (min.) above Slab 4-in. (min.) reinforced concrete Slab Sloped at 1⁄8 in. per ft. to front of garage concrete-rated moiSture barrier compacted gravel or pea gravel foundation wall & footing note a Stronger concrete mix iS required for a garage Slab than for a Slab in living SpaceS. verify local requirementS.
Hot expanSion joint at all edgeS of unheated garage Slab Cold Waste plaStic-Sleeve pipe inSulation iSolateS water pipeS from Slab.
1-in.-thick fiberglaSS wrap inSulation iSolateS waSte pipeS from Slab.
note
uSe type k or type l copper Supply pipeS. minimize brazed fittingS below Slab. hot-pipe inSulation iS recommended.
note
uSe abS plaStic waSte lineS. no cleanoutS are allowed below Slab. Set cloSet flange at f.f.l. and anchor directly & Securely to Slab.
perimeter inSulation required
See 22b, c & d
Slab with turned- down footing or Slab with foundation wall
See 23b
pex tubing at 8 in. o.c. (approx.) tied to rebar or wire meSh
4 in. (min.) reinforced concrete Slab optional inSulation concrete-rated moiSture barrier cloSed-cell rigid inSulation (2 in. min.) to 4 ft. from perimeter
4 in. (min.) of gravel
Diagram of Radiant Heat Tubing Slab
tubing
heat Source
note
croSS-linked polyethylene tubing (pex) haS replaced copper tubing aS the conveyor of hot water for radiant SlabS. thiS elaStic tubing iS Supplied in long rollS & can cover about 200 Sq. ft. without any jointS below the Surface. the addition of inSulation below the Slab will improve the perfor mance of the SyStem.
T
he floor is the part of the building with which we have most contact. We walk on the floor and, on occasion, dance, wrestle, or lie on it. We can easily tell if the floor is not level, if it is bouncy or squeaky, and this tells us something about the overall quality of the building. The floor carries the loads of our weight, all our furniture, and most of our other possessions. It also acts as a diaphragm to transfer lateral loads (e.g., wind, earthquake, and soil) to the walls, which resist these loads. Floors insulate us from beneath and often hold ductwork, plumbing, and other utilities. So a floor must be carefully designed as a system that integrates with the other systems of a wood-frame building—the foundation, walls, stairs, insulation, and utilities. Once designed, the floor must be carefully built because so many subsequent parts of the construction process depend on a level and solid floor construction.ELEMENTS OF A FLOOR SYSTEM
There are several floor-construction systems, and all of them are composed of variations of the same basic ele- ments: support, joists, and a subfloor.
Support—Wood floor systems usually span between parallel supports. These supports may be a foundation wall, a stud-bearing wall, or a beam. The first two are covered in Chapters 1 and 3, and beams are a subject of this chapter (see 29-31).
Joists—The primary structural members of a floor system are the joists, which span between the supports. The most common materials for joists are solid-sawn lumber (see 35-42) and engineered wood I-joists (see 43-44). Joists are usually placed on 12-in., 16-in., or 24-in. centers, depending on the required span and the sizes of the joists (see 32).
Subfloor—The planar structural surface attached to the top of the joists is called the subfloor (see 48-51). The subfloor provides the level surface to which the finish floor is applied, and it also acts as a diaphragm to transfer lateral loads to the walls. Subfloors are usually made of plywood or oriented strand board (OSB) but may also be made of other materials. Some subfloors also provide mass for passive-solar heating.
FLOORS AND WALLS
It is essential to coordinate the details of a floor-framing system with those of the wall framing. There are two wall-framing systems from which to choose:
Floors
c h a p t e r
2
Subfloor JoiSt
Stud wall beam
foundation
Solid-Sawn
Balloon framing—Balloon framing is a construction system in which the studs are continuous through the floor levels. It is a mostly archaic system, but there are some situations where balloon framing is appropriate. These situations are discussed in the introduction to Chapter 3 (see 65-66). Balloon-framing details that per- tain to floors are included in this chapter.
Platform framing—Platform framing is the domi- nant wood-floor construction system in this country. The platform frame floor is so named because the stud-wall structure stops at each level, where the floor structure provides a platform for the construction of the walls of the next level. This chapter concentrates on platform framing, which has two basic variations: joists with structural panels (OSB or plywood), and girders with decking.
TYPES OF FLOOR FRAMING
Throughout the history of the balloon frame and the more recent platform frame, floors have typically been made with joists (2x6, 2x8, 2x10, and 2x12) that are spaced closely (usually 16 or 24 inches on center) to support a subfloor that spans between them.
For 125 years, the joists were all solid-sawn lumber, and the subfloor started as boards, laid diagonally and later became plywood. In the past 35 years or so, solid- sawn lumber has been slowly replaced with engineered wood products—wood I-joists and other structural composite lumber (SCL). Engineered wood products are straighter, more dimensionally stable, and generally stronger than their solid-sawn counterparts. In addi- tion, they can be made larger and longer than sawn lumber, so they can span farther.
Currently, engineered wood products have over- taken solid-sawn lumber in terms of market share for floor construction, but both materials are still widely used. Subfloors are now typically made with Oriented Strand Board (OSB) instead of the more expensive plywood.
Most of the details in this chapter are illustrated with examples showing solid-sawn lumber—primarily because the drawings are more clear using these simple forms. However, the solid-sawn details may be inter- preted to be built of engineered products because the basic principles apply to all types of framing mate- rial whether solid-sawn, I-joist, or other composite materials. Because I-joists require special treatment in certain conditions, there is a section of the chapter devoted entirely to I-joists (see 43–44).
In areas where timber is plentiful, 4x girders with 2-in. tongue-and-groove subfloor decking that spans 4 ft. are often used as a floor system (see 46–47). Lower grades of decking on girders make a very eco- nomical floor over crawl spaces, and appearance grades of decking are often used for exposed ceilings. The decking itself does not technically act as a diaphragm to resist lateral loads, so it may require additional diagonal structure, especially at upper levels.
Also included in this chapter are porch and deck floors, floor insulation, and vapor barriers.
Subfloor
JoiSt
16 in. or 24 in. Spacing