Weathering Walls : FPL Helps Buildings and Builders Breathe Easy

At the core of combating the cold in residential structures is effective insulation — but keeping warmer at home is not as simple as plastering as much polystyrene as possible to your walls and floors. Using more plastic insulation on exterior walls is a surefire way to increase the thermal efficiency of a building, but before you remodel, consider that you may be trapping more than just heat inside of your house.

Popular types of extruded and expanded polystyrene insulation have a much lower permeability than typical wooden building materials such as plywood and oriented strandboard. Because of this, exterior walls may become moisture traps, allowing moisture to enter, but not evaporate. This low-drying potential may lead to the mold growth, and in some cases, decay of walls made with these wood structural panels (WSPs). Unfortunately, little data exists on the real-world performance of these wall combinations, but researchers at the Forest Products Laboratory (FPL) are out to change this.


Wood structural panels (WSPs) are mainstays in residential and commercial construction.


FPL, in cooperation with APA – The Engineered Wood Association and Washington State University, has been studying the hydrothermal performances of walls constructed with WSPs since 2014. Performance testing in the Pacific Northwest was completed last last year, but data for cold climate zones, like FPL’s hometown of Madison, Wisconsin, is still being collected.

Researchers have constructed a “test hut” in Madison using wall assemblies with exterior continuous polystyrene insulation installed over WSPs. In this hut, they will investigate the potential for moisture accumulation and the drying capability of the walls during the colder months of the year.


The interior of the Chamber for Analytic Research on Wall Assemblies exposed to Simulated Weather (CARWASh) at FPL.


But FPL researchers don’t have to wait for the leaves to fall for the testing to begin. Using the on-site weathering chamber, the CARWASh, researchers will be able to run tests on individual wall sections in a computer-controlled and monitored environment. A total of 16 wall assemblies, each 4 feet wide and 7 feet tall, will be tested. Various combinations of water-resistive barriers, and exterior insulation will be used in the test walls, and the CARWASh will provide realistic weather perimeters and controlled water injections to simulate rain intrusion.

The test hut hygrothermal monitoring and CARWASh studies will be completed by July 2016, and the final report will be prepared by September.

With this data, WSP manufacturers will finally know how their products preform when the temperature goes down and the humidity goes up, and whether or not the permeability of the wood balances the impermeability of the insulation. Furthermore, as contractors make improvements to existing structures, and engineers design new buildings to comply with increasingly demanding energy-efficiency codes, they will have peace of mind thanks to FPL research — and breathe a little easier, knowing that their buildings will do the same.

For more information, see this Research in Progress report.

Senator Tammy Baldwin tours FPL

U. S. Senator Tammy Baldwin (D-Wis.) visited the Forest Products Laboratory on Friday, August 9th, to meet with FPL leadership and learn more about how research at the Lab benefits the American public.

baldwin1FPL Director Michael Rains welcomes Senator Baldwin in the Centennial Research Facility lobby and provides an overview of FPL research.


Assistant Director Michael Ritter and Sen. Baldwin take a look inside the Lab’s one-of-a-kind weathering chamber and discuss wood durability research.

In the composites research area, materials engineer Ron Sabo (left) and Assistant Director Ted Wegner (right) explain how composites can use low-value or waste material to create high-quality wood-based products.
baldwin5In the Engineering Mechanics and Remote Sensing Laboratory the group takes a look at the strong floor and discusses how researchers use this unique space to gain a better understanding of the physical properties of wood and wood products. (L to R, Assistant Director Mike Ritter, Director Michael Rains, Senator Tammy Baldwin)

FPL chemist Alan Rudie explains the wonders of wood-based nanotechnology to Senator Baldwin in the Nanocellulose Pilot Plant.

USDA Secretary Tom Vilsack tours the FPL


FPL Leadership provided a summary of recent accomplishments to Secretary Vilsack and staff.

Led by Acting Director Michael Rains, the Forest Products Laboratory (FPL) recently welcomed USDA Secretary Tom Vilsack for a tour through its unique and growing set of research facilities. Basic and applied research at FPL supports a number of USDA and Forest Service objectives, including forest management and restoration, the wise use of forest resources, job creation, and expanding economic opportunities through public-private partnerships on a national scale.

Throughout his tour, Secretary Vilsack talked with lab leadership about FPL’s diverse and innovative research efforts. Project leaders used the opportunity to field questions from the Secretary and explain work ranging from wood preservation and durability to advances in “green” building strategies and technology, use of beetle-killed trees, work on historic timber bridges, and advances in nanocellulose-related materials and applications.


Supervisory Microbiologist Carol Clausen briefs Secretary Vilsack on FPL’s Moisture Test Facility.

In FPL’s unique weather testing facility, project leader Carol Clausen described how wall assemblies can be tested for a range of harsh conditions, from heavy rain and extreme heat to high humidity and strong winds. “Developing durable building materials for green construction is a win-win situation for the Nation’s forests and the American people,” Clausen told Vilsack. “Utilizing beetle-killed trees to create value-added products, improves forest health, reduces the wildfire threat, and creates jobs.”


Supervisory Engineer Bob Ross discusses recent FPL research on a 2,500-year-old wooden mummy coffin.

In the Engineering Mechanics and Remote Sensing Laboratory, project leader Bob Ross brought out the big gun, an air-powered debris launcher used to develop protective safe-rooms in hurricane and tornado-prone areas. The Secretary watched as this unique air-cannon blasted an eight-foot 2×4 board into a test wall of cross-laminated material at over 100 miles per hour.


Supervisory Research Chemist Alan Rudie tours Secretary Vilsack through FPL’s new Nanocellulose Pilot Plant and shows nanocellulose samples.

In the world renowned Nanocellulose Pilot Plant, project leader Alan Rudie guided the Secretary through some of FPL’s most advanced equipment. Very strong and extremely versatile, nanocellulose materials can be used for a variety of applications including ballistic glass; small, powerful transistors; and heat-resistant additives for concrete, among many other uses.

Zhiyong Cai, project leader for FPL’s engineered composite science unit, demonstrated uses for cellulose nanofibrils material in bio-degradable electronic parts, high-performance insolation aerogel material, and regenerated cellulose braided reinforced fabric.

“The Secretary was very interested in nanotechnology applications in forest products research,” said Cai. “He was impressed with the impact that cellulose nanomaterial could bring to not only the forest products industry, but also electronics and other industries.”You can view more photos of the Secretary’s visit, including a slow-motion video of the hurricane-force 2×4 hitting a cross-laminated wall assembly, at FPL’s main site.

# # #

By James T. Spartz, FPL Public Affairs Specialist.