Send Letter to Editor
Research with a practical payoff | Engineering wood products
Battling moisture and mold
A testing ground for home improvement
FPL projects in Wisconsin
In the next five years, Wisconsinites will build some 130,000 new homes. Nationwide trends predict another seven or eight million new houses, joining the 76 million or so existing single-family houses. The vast majority will be constructed largely of wood, and every house, whether wood-framed or not, will incorporate technologies, materials or design features that were developed or studied at the Forest Products Laboratory (FPL) in Madison.
Since 1910, this lab of the U.S.D.A.'s Forest Service has grown to include a workforce of botanists, chemists, economists, engineers, microbiologists, mycologists and technicians who put wood through its paces in a cluster of buildings at the western end of the University of Wisconsin campus. Their research leads to new building codes and engineering standards, new wood products, and new procedures for making paper or building houses.
The lab complex includes some impressive machinery whose sole purpose is to torture and destroy wood to test its properties. Another building contains a pilot plant for testing papermaking innovations. FPL's headquarters houses collections of 103,000 wood specimens from around the world as well as 14,000 specimens of wood-decaying fungi.
Current wood research is examining mechanical and physical properties of woods, wood deterioration and preservation, fungus and mold growth, papermaking, "deconstruction" of old buildings, wood adhesives and sealants, engineered lumber, wood-fiber filters, ethanol production, moisture control, and new uses for small-diameter timber. Much of the research has practical applications for house construction and maintenance. The facility includes a full size, four-bedroom house, built in 2001 to showcase and evaluate building materials and building techniques.
"Housing accounts for 80 percent of the solid wood products used in the United States, so it's a natural high priority area for the Forest Service and FPL," said Chris Risbrudt, economist and director of Forest Products Lab since 2001. Government has broad interests in ensuring that houses remain durable and affordable, Risbrudt said.
"Home building, improvement and maintenance are important sectors in our national economy," he noted, "and for most Americans, buying a home represents the largest investment most of us make in our lifetimes."
Research with a practical payoff
FPL researchers have investigated a wide range of housing issues that proved to have practical applications. One early project analyzed the structural qualities of different woods. The resulting data showed many species of wood are suitable for constructing houses and formed the basis for national standards in grading lumber. Studies of wall condensation in the 1930s led to the first recommendations for using vapor barriers. The 1935 one-volume encyclopedia, Wood Handbook: Wood as an Engineering Material, remains a builder's bible on working with wood as a structural material. It has been updated numerous times, most recently in 1999. A system of classifying and grading paints helps consumers choose the most appropriate coating for a particular application.
The first all-wood prefabricated house was built using plywood panels at FPL in 1935; two more demonstration houses were erected in 1937. The designs helped provide low-cost housing during the depression. FPL's "Techniques of House Nailing" instructed apprentice carpenters and homeowners who bought more than 100,000 copies from 1947-57.
More recently, the FPL established an Advanced Housing Research Center (AHRC) opened in 1999 to lead to even more efficient use of available woods. Though trees are plentiful, renewable and recyclable, demand for building materials is equally strong.
Ninety-five percent of U.S. homes are still wood-framed, and homes are getting much bigger. In 1950, the average single-family home was a little less than 500 square feet; by 2000, homes averaged 2,226 square feet. Lumber use per home increased from about 11,000 board feet per home in 1962 to 14,000 board feet by 1998. The use of "structural panels" – plywood and oriented strand board (OSB) – quadrupled from 3,000 square feet per home to more than 12,000 square feet in the same time period. Total wood consumption climbed accordingly. From 1962 to 1998 lumber use for homebuilding jumped from about 14 billion board feet annually to more than 22 billion board feet; structural panel use skyrocketed from about four billion square feet to 19 billion square feet.
FPL is pursuing three strategies: One area of research aims to extend the useful life of wood products to limit water and wind damage. We are assessing better wood preservatives and coatings as well as testing construction techniques, Risbrudt said.
Second, we continue to look for ways to use forest that traditionally were passed over by the construction trades and papermakers. For instance, OSB can be readily made from aspen and other softer woods. Oriented strand board is composed of thin wood strips laid at cross angles and glued with heat-cured waterproof adhesives. The resulting panels are strong like plywood but have no laps, gaps, grain or voids for added strength.
Third, we are much more serious as a society about reusing and recycling wood products to reduce the need to cut trees, Risbrudt said.
All three strategies have their place in our housing research, and all three have taken on a sense of urgency in the past few years, according to Mike Ritter, FPL assistant director and director of the AHRC. "Not long ago, large logs from old-growth trees could be sawn into the thick, long, high-quality lumber required for beams and joists. Those trees aren't available anymore; we now rely on lumber from managed tree plantations and wood from smaller tree species."
Engineering wood products
To meet the nation's construction needs, FPL and others have developed varieties of manufactured or engineered wood products that have become standard in home building today. These includes I-joists that combine an upright panel made of plywood or OSB with composite lumber. The top parts of the beams are made of thin strips of wood veneer that are glued and laminated together. Lumber for homebuilding can also be recovered by carefully deconstructing and salvaging old buildings such as decommissioned military bases scheduled for closure. FPL researchers are working closely with the U.S.Army, Habitat for Humanity and others to explore the possibility of salvaging millions of board feet of high-quality lumber that had been used to build thousands of barracks, warehouses and other buildings more than a half-century ago. Since the government has stopped maintaining activities in many of these unused buildings, the lumber will deteriorate unless deconstruction begins soon.
Battling moisture and mold
Protecting wood against moisture has been an FPL priority since the lab's founding. "The greatest challenge to ensuring a durable house is managing moisture," said Ritter. Moisture can come from leaky roofs or windows as well as from inadequately vented bathrooms or laundry rooms.
Home moisture has gotten more attention since expensive insurance claims and lawsuits raised public awareness about molds. In 2002, insurance companies paid out $2.5 billion in mold-related claims. At year's end, more than 24,000 claims and thousands of lawsuits were still outstanding. While excess mold raises health concerns like allergic reactions or may irritate asthma symptoms in sensitive people, most authorities agree there is less convincing medical evidence that building molds are deadly.
Mold is a superficial problem for wood; it appears on the surface and does not weaken the wood or pose structural problems. In fact, almost all buildings contain some mold. A University of Arizona researcher recently studied 160 houses in seven cities around the United States. Every house studied had mold somewhere.
Molds indicate that buildings have unwanted moisture. That moisture makes wood less durable by causing it to expand and contract, loosening joints and fasteners, or promoting the growth of certain fungi that cause decay.
Several factors contribute to the apparent increase in moisture problems in new homes. Builders are putting up larger houses that tend to have complicated roof designs with dormers, skylights and many valleys, corners and hips that require special treatment to prevent leaks. Some new building materials and technologies require more careful installation. In some designs homes are so tightly sealed that trapped moisture has little opportunity to dry out.
A testing ground for home improvement
To help remedy these issues, two industry trade groups, APA-The Engineered Wood Association and the Southern Pine Council, joined with FPL to build a unique research demonstration house on the laboratory grounds in Madison. Each step of construction was videotaped for use in training carpenters and others in proper construction techniques. Eventually, more than 50 companies and organizations assisted in the project by supplying materials, appliances and equipment.
The house, which continues to be used for research, has moisture sensors throughout.
In addition to learning how moisture moves within the building, FPL's research will eventually lead to better management of that moisture by improving house design and constructionas well as recommending procedures for operating the house's mechanical systems to manage air flow and humidity in finished homesRitter said. The four-bedroom, 2,200 square-foot house followed a standard contemporary design and was built by one of the Madison area's leading homebuilders. The house now sits on a small landscaped lot in front of FPL's headquarters building and is open to the public for scheduled tours.
Its unique features include cutouts in walls, floors and ceilings that show visitors construction details and materials such as finger-jointed studs and cellulose insulation. "The house design features a number of construction details intended to prevent unwanted moisture," said Ritter. The roofing material is a wood-plastic composite developed at FPL and made from recycled milk jugs and sawdust. The shingles contain additives to lessen the weathering effect of sunlight and are expected to last up to 50 years.
The house also features a wood foundation, constructed of pressure-treated southern pine lumber and plywood based on a concept developed at FPL. Such foundations may have several benefits. This one was built in the middle of a Wisconsin winter when it would have been difficult to build a masonry or poured concrete foundation. A wood foundation can also be insulated and finished to create additional dry, warm living space.
Most floors in the house are made of southern pine, though the kitchen is maple. One of the bedroom floors is made of wood salvaged from a deconstruction project and another uses small-diameter wood boards. Carpets are made from recycled plastic bottles.
Following the successful house collaboration, several wood associations and the FPL launched a Residential Moisture Management Network. The network is one more outreach tool to coordinate both research and information coming from government agencies and building trade groups, Ritter explained. "Manufacturers and suppliers need to provide builders and homeowners with clear, consistent recommendations to manage house moisture in ways that lead to healthy, durable homes," Ritter said. "Our work at the Forest Products Lab will continue to look for practical applications that incorporate wood and wood products as stronger, durable, fire-resistant and attractive building materials."
To contact FPL with a question about using or preserving wood, or to schedule a group tour of the Research Demonstration House or laboratory, phone (608) 231-9200, e-mail: Forest Products Laboratory, write Public Affairs, Forest Products Laboratory, One Gifford Pinchot Drive, Madison, WI 53726-2398, or visit Forest Products Laboratory
George Couch is a public affairs specialist with the U.S.D.A. Forest Service's Forest Products Laboratory in Madison.