PWF Perfection: FPL Demo House 15 Years Later

The following blog has been adapted from The Wood Handbook, Wood as an Engineering Material.

Light-frame buildings with basements are typically supported on cast-in-place concrete walls or concrete block walls supported by footings. This type of construction with a basement is common in northern climates.

Another practice is to have concrete block foundations extend a short distance above ground to support a floor system over a “crawl space.” In southern and western climates, some buildings have no foundation; the walls are supported by a concrete slab, thus having no basement or crawl space.

The Research Demonstration House was built in 2001 for research and education at FPL.

The Research Demonstration House utilizes a wooden basement, and was built in 2001 for public education and scientific studies at FPL.

But treated wood can also used for basement foundation walls. Basically, such foundations consist of wood-frame wall sections with studs and plywood sheathing supported on treated wood plates, all of which are preservatively treated to a specified level of protection. To distribute the load, the plates are laid on a layer of crushed stone or gravel.

The walls, which must be designed to resist the lateral loads of the backfill, are built using the same techniques as conventional walls. The exterior surface of the foundation wall below grade is draped with a continuous moisture barrier to prevent direct water contact with the wall panels. The backfill must be designed to permit easy drainage and provide drainage from the lowest level of the foundation.


The wooden foundation was constructed during the brutal Wisconsin winter, where conventional masonry would have been difficult.

Because a foundation wall needs to be permanent, the preservative treatment of the plywood and framing and the type of fasteners used for connections are very important. A special foundation (FDN) treatment has been established for the plywood and framing, with strict requirements for depth of chemical penetration and amount of chemical retention. Corrosion-resistant fasteners (for example, stainless steel) are recommended for all preservative-treated wood.

This construction technique is exemplified at the Forest Product Laboratory’s (FPL) Research Demonstration House (take a virtual tour here). The basement walls and floor are constructed of pressure-treated Southern Pine lumber and plywood to create the permanent wood foundation (PWF). The PWF is designed to resist and distribute earth, wind, and seismic forces and resist termite attack.

Thanks to insulated walls, the basement of the Research Demonstration House stays warm year-round.

Thanks to insulated walls, the basement of the Research Demonstration House stays warm year-round.

The walls consist of nominal 2- by 10-inch treated lumber supports and nominal 3/4-inch-thick plywood sheathing. The basement of the Research Demonstration House was constructed in freezing temperatures during the middle of winter when construction of a masonry or poured concrete foundation would have been very difficult.

For more than a decade, the basement of the Research Demonstration House has stayed dry, warm, and structurally sound thanks to expert engineering and it’s PWF. It stands as an example of how wood, usually reserved for above-ground construction, can be a valuable subterranean asset, and pushes the boundaries of what can be done with mankind’s most important building material.

For more information on the use of wood in buildings and bridges, please see Chapter 17 of The Wood Handbook, Wood as an Engineering Material.

Helping on the Home Front: War-Worn Wood Relishes in Retirement

From building aircraft parts during times of metal scarcity to educating Department of Defense employees on the best ways to package materiel for shipment to the front lines of World War II, researchers at the Forest Products Laboratory (FPL) have always been willing to lend a hand to support the military in a time of need.

But sometimes, the mission is less conventional than providing for an operational force in a foreign land.

The Wood Crate Design Manual is a popular historic example of FPL research in collaboration with the Department of Defense.

Here in the United States, the U.S. Army estimates that there are over 250 million board feet of lumber and timber in World War II-era buildings slated for demolition. Since the 1990s, FPL scientists have worked cooperatively with the Army to recycle and reuse more than 4,700 cubic meters of this lumber and timber in new construction projects.

To find this in action, look no further than the Research Demonstration House at FPL. The flooring in one of the upstairs bedrooms is made of old-growth Douglas fir salvaged from military barracks originally built in the 1940s. The flooring material was provided by the Ft. Ord Reuse Authority in Marina, California, and stands in contrast to the adjacent room, which uses new, albeit small-diameter, Douglas fir. In addition to keeping wood out of landfills, the floor bears the character of 60+ years of military service, including original nail holes from its previous career.

Recycling this material has been limited by a lack of appropriate science-based grading rules and engineering design values, and consequently, much of it ends up as waste in landfills. FPL researchers continue to work on developing new and accurate grading systems to ensure that residual properties of recycled lumber and timber will meet the performance requirements of new applications. This way, with scientific data and performance information, industry and design professionals can be confident the integrity of their buildings is not compromised.

The military is only one potential source of recycled wood, however, as it is estimated one billion board feet of lumber is landfilled in the United States each year. Deconstruction offers a means of reusing this material for valuable products, and in some cases, recycling operations can provide economic opportunities for local communities.


FPL’s Research Demonstration House is home to a host of innovative approaches for using wood. A bedroom on the second floor utilizes recycled Douglas fir provided by the U.S. military.

Although these efforts are sometimes overshadowed by the wooden propeller and ship manufacturing industry of years ago, they play an important role in this nation’s defense industry. Recycled lumber and timbers in new construction conserves existing forests, encourages the most efficient use of harvested materials, and makes our military, forests, and communities stronger.

For more information, please see FPL publications Evaluation of Lumber Recycled from an Industrial Military Building, and Engineering Evaluation of 55-year Old Timber Columns Recycled From an Industrial Military Building.

January is National Radon Action Month: Test Your Home and Protect Your Health

The hustle and bustle of the holiday season is over and here in Wisconsin, the weather is cold. Our doors and windows are closed, and that’s one of the first steps in getting good results from a radon test.

Radon is the second leading cause of lung cancer.

Radon is the second leading cause of lung cancer.

Radon is a radioactive gas that results from the natural breakdown of uranium in soil, rock, and water. It is the second leading cause of lung cancer overall and the leading cause in non-smokers. The EPA estimates that as many as 21,000 lung cancer deaths a year are caused by radon. Radon is colorless and odorless, and the only way to know if your home has a problem is to test for it.

By now you are asking, “What does radon have to do with the Forest Products Laboratory?” Radon was detected in the basement of the FPL’s Research Demonstration House, an unoccupied residential structure built in 2001 on a permanent wood foundation. This discovery took place during a case study focused on estimating the rate of moisture infiltration from soil surrounding the basement foundation. Initial test results showed an average of 8.7 picocuries per liter (pCi/L) of radon in the basement of the house during winter – far above the EPA action level guideline of 4 pCi/L. Researchers C.R. Boardman and Samuel V. Glass took advantage of the installation of the radon mitigation equipment to validate the moisture infiltration model used to estimate the rate of moisture entry. In a  follow-up study, they monitored both moisture infiltration and radon levels for 1 year. The active soil depressurization system, a standard radon mitigation technique, reduced basement radon levels to below 1 pCi/L and reduced moisture infiltration by over 75% during the winter. The final in-depth report, “Basement Radon Entry and Stack Driven Moisture Infiltration Reduced by Active Soil Depressurization,” was recently published in the February 2015 edition of Building and Environment.

The EPA and the U.S. Surgeon General recommend testing all homes for radon. If levels are high, take steps to lower them. Reliable techniques exist for reducing radon levels in homes. Research by public and private agencies, years of extensive hands-on mitigation experience, and long-term follow-up studies on the durability of radon mitigation systems have formed a strong knowledge base of proven mitigation techniques for homes, schools, and commercial buildings. The techniques are straightforward, and for a typical single-family residence, can be done in one day by a qualified contractor.

Take a step to protect your health and purchase a radon test kit or hire a contractor today.

To learn more about radon, visit and see to locate your state radon program.