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INTRODUCTION � �� The Permanent Wood Foundation gravel,coarse sand or poured concrete. " (PW�is an innovative building system _ The footings distribute the vertical load that saves builders time and creates com- .. from the structure to the soil. fortable,warm living areas that enhance - _ �, � The recommendations for foundation a home's salability. �!� sheathi.ng,studs and connections are . Just what exactly is a Permanent r' �,�'� based on thorough design analysis, - � Wood Foundation? It's a load-bearing " -- { developed by experks of the wood prod- lumber-framed foundation wall sheathed - ucts industry and the National Associa- � with plywood. All l�mmber and plywood � + ' tion of Home Birilders Research components in the wood foundation are � �� Foundation,Inc.These recommendations pressure-treated with preservatives to provide a quality"engineered"foimda- withstand decay from moisture and insect damage. tion system that resists backfill and wind or seismic The PWF is an engineered foundation construction loads. The detaiLs are applicable for most common system. The engineering design analysis was devel- construction applications in a variety of soils. oped jointly by the U.S.Department of Agricult�e's In larger or more complea buildings,engineering Forest Service,the American Forest&Paper Associa- may be necessary because of differing structural tion(AF&PA),and the American Wood Preservers requirements. ff so,refer to Permanent Wood Foun- Instiiute(AWPn,with field evaluations by the National dation System: Design,Fabrication and Installation Association of Home Birilders Research Foundation, Manua� (DFI Mannan,available from the American Inc. Additional laboratorq and in-ground structural Forest&Paper Association. It contains complete . testing has been conducted by APA-the Engineered design data and is the source of some of the tabular . - Wood Association. materials and many of the detaiLs given in this guide. � Durability of the system is demonstrated by long- PWF construction is similar to wood-frame exteri- term in-ground tests conducted by the Forest Service. or wall construction,with some exceptions. Because In these tests,pressure-treated wood has withstood PWF walls aze used in below-grade applications,all severe decay and termite conditions over decades of lumber and plywood is pressure-treated with preser- exposure. PWF walls aze designed to resist and dis- vatives for decay and termite resistance. Other dif- tribute earth,wind,seismic loads and stresses that ferences include the use of stainless steel na�s,an may crack other types of foundations. offset footing-plate,and framing anchors to connect The Permanent Wood Foundation is accepted by foundation studs and floor joists to the top plates of the major model building codes,by federal agencies, foundation walls in high backfill conditions. and by lending,home warranty,and fire insnrance Like conventional wood-frame walls,the wood institutious. And�t has heen proven by years of suc- foimdation is adaptable to virtually any design. It fits cess in more than 300,000 homes and other struc- a variety of floor plans and can be used for both level tures throughout the U.S. and sloping sites. This guide describes the features and advantages In certain localities where emission of radon gas of Permanent Wood Foundations. And it provides from the soil or ground water is prevalent,a plastic builders and architects with detailed construction pipe and tee can be installed through the basement tips for a variety of building styles,including both floor for basement-type PWFs. For crawl space crawl space and full basement foundations. PWFs,a perforated plastic pipe can be installed on A PRovEx PRacnca�SrsrEM �e ground inside the crawl space,beneath the vapor � retarder. In both applications,the pipe is connected Permanent Wood Foundations consist of load- to a vent pipe and eachaust fan to depressurize the bearing walls framed with pressure-treated lumber soil under the basement floor or crawl space vapor and sheathed with pressure-treated APA-trade- retarder,removing radon gas from the soil under and marked plywood(see Figure 1). The walls are around the building. If a sump is used,the sump designed to withstand backfill and vertical loading. cover should be sealed and connected to the vent They are supported laterally at the top by the floor pipe and exhaust fan to remove radon gas from the system, at the bottom by a cast-in-place slab or pres- sump pit. sure-treated wood basement floor,and at the base by bacl�'ill and foundation footings of crushed stone, pWF DEs[crt&Coxs'ncucrtox Gu�nE SOUTHERN PINE COUNCIL . '