Building Code Relationships to Wood Use for Floor-Foundation Systems of Single-Family Houses

Building code requirements for floor-framing of crawl-space, concrete slab, wood pole frame, and wood underfloor plenum systems of construction for single-family houses were evaluated. Data were obtained from building officials of 25 major cities in 12 states extending across southern United States. All of the cities enforce building codes, primarily one of the four model codes: Basic, National, Southern Standard, or Uniform Building Codes. Protection requirements for wood floor-framing differ in accordance with method of construction and the building code provisions enforced. For concrete slab-on-ground construction, use of wood screeds or sleepers on the slab is preferred when installing wood strip finish flooring. When wood block flooring is used, in 23 of the 25 cities it is installed in mastic applied directly on the slab. Memphis, Miami, and Norfolk required the use of a vapor barrier between the concrete slab and the wood finish flooring, but 11 cities specified placement of the vapor barrier between the ground and the slab. For crawl-space construction, pressure treatment is generally required for wood floor joists closer than 1.8 inches above ground, and for wood girders less. than 12 inches above the ground. Concrete slab-on-ground construction has replaced crawl-space construction for single-family houses in many southern states, and is the dominant system presently used. Of the 25 cities studied, only Atlanta, Georgia and Fresno, California had witnessed an increase in crawl-space construction between 1963 and 1968. Slab construction uses about 4/10 less lumber and 1/3 less plywood than comparable houses of crawl-space construction. Pole frame construction for single-family houses is permitted in 16 of the 25 cities. Objections to pole framing by officials of the nine remaining cities were general and could be overcome with simple revisions in design or construction. Thirteen cities would permit a wood floor-framing system with a ductless underfloor plenum for distributing warm and cool air. It provides advantages of comfort and cost. Depending on location, cost savings of several hundred dollars can be realized over slab-on-ground construction for comparable houses. Objections to the plenum by the 12 cities which would not permit its use were centered around fears relating to fire and to wood damage by termites and decay. Many of these doubts can be dispelled by dissemination of factual information based on plenum research results.

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