All-Weather Wood Foundations | |
A frequent consumer question concerns the advisability of using wood foundations, rather than using the more familiar concrete foundation construction. Treated lumber has been used for foundations for several decades, but industry acceptance of the practice was slow in developing. It was difficult for both builders and consumers to accept that wood buried in the earth would not quickly decay. But press information was released concerning a wood house foundation, located in Wisconsin, that was more than 30 years old. The foundation was dug up and inspected, and was found to have survived the 30 years without any damage from moisture or insects. Wood foundations can be used either for houses with crawl space or for full basement construction. The key to success in using wood foundations is to provide for proper drainage around the wood footings, to wrap the foundation walls in protective polyethylene plastic film, and to build foundation walls using treated lumber that is suitable for ground contact. Building wood foundations is a job that is best left to professionals who have experience in the work. The basic procedure is to dig and level the trenches for the footings. Several inches of gravel, sand, or crushed rock is placed in the footing excavations, then it is leveled and tamped. Use a treated 2x12 as a footing and nail it to the bottom plate of the foundation wall. The all-wood foundation wall is framed just like an above-ground wall, except treated lumber is used in construction. The studs used are treated 2x6s, or larger, depending on the type of soil, the width of the house and whether it is 1 or 2 stories high. The framed wall is covered with treated plywood, the thickness of which again will depend on the loads the walls will carry and the type of soil. After the plywood is in place, the entire wood foundation (exterior) is wrapped with a polyethylene plastic film to help keep the structure dry. On a full wood basement wall, the concrete floor is poured on the inside to prevent the bottom of the wall from tipping in, and the exterior side of the wall is backfilled with gravel and earth, then graded to ensure that water runs away from the house. If the wood wall is a foundation for a crawl space and is not full basement height, the wall is stabilized with earth backfill from both interior and exterior sides. The wood foundation system is usually cheaper than a poured concrete or a concrete block foundation. The wood foundation can be built in a factory and hauled to its location for installation, which is a definite plus for construction in cold climates where pouring concrete in winter is difficult. In place, the wood foundation is warmer than concrete, and has stud cavities that can be filled with fiberglass batt insulation. The wood construction makes the basement easier for the do-it-yourselfer to finish, because concrete basement walls are more difficult for the homeowner to finish alone. For more information about the all weather wood foundation system, contact the National Forest Products Association, 1619 Massachusetts Avenue N.W., Washington DC 20036. Written by Gary Branson Reprinted with permission. Copyright HouseNet, Inc. |