Joint Types Top Ten: Vocab for the Wood Wise

According to the Wood Handbook, Wood as an Engineering Material, a joint is the junction of two pieces of wood or veneer. Researchers at the Forest Products Laboratory (FPL) take this a step further, and identify at least 10 different types of joints.

  • Adhesive Joint — The location at which two adherends are held together with a layer of adhesive.
  • Assembly Joint — Joints between variously shaped parts or sub assemblies such as in wood furniture (as opposed to joints in plywood and laminates that are all quite similar).
  • Butt Joint — And end joint formed by abutting the squared ends of two pieces.
  • Edge Joint — A joint made by bonding two pieces of wood together edge to edge, commonly by gluing. The joints may be made by gluing two squared edges as in a plain edge joint or by using machined joints of various kinds, such as tongued-and-grooved joints.
  • End Joint — A joint made by bonding two pieces of wood together end to end, commonly by finger or scarf joint.
  • Finger Joint — An end joint made up of several meshing wedges or fingers of wood bonded together with an adhesive. Fingers are sloped and may be cut parallel to either the wide or narrow face of the piece.
  • Lap Joint — A joint made by placing one member partly over another and bonding the overlapped portions.
  • Scarf Joint — An end joint formed by joining with adhesive the ends of two pieces that have been tapered or beveled to for sloping plane surfaces, usually to a featheredge, and with the same slope of the plane in respect to the length in both pieces. In some cases, a step or hook may be machined into the scarf to facilitate alignment of the two ends, in which case the plane is discontinuous and the joint is known as a stepped or hooked scarf joint.
  • Starved Joint — A glue joint that is poorly bonded because an insufficient quantity of adhesive remained in the joint.
  • Sunken Joint — Depression in wood surface at a joint (usually an edge joint) caused by surfacing material too soon after bonding. Inadequate time was allowed for moisture added with the adhesive to diffuse away from the joint.

For more information about joints, bonding wood, and adhesives, please see the Wood Handbook, Wood as an Engineering Material.

Certifiably Sustainable: Systems That Safeguard Forests

Researchers at the Forest Products Laboratory (FPL) work with several different certification authorities when developing new technology.

Researchers at the Forest Products Laboratory (FPL) work with several different certification authorities when developing new technology.

Unlike metals and fossil-fuel-based products (such as plastics), our forest resource is renewable and with proper management a flow of wood products can be maintained indefinitely.

The importance of forest-based products to our economy and standard of living is hard to overemphasize — half of all major industrial raw materials we use in the United States come from forests.

However, the sustainability of this resource requires forestry and harvesting practices that ensure the long-term health and diversity of our forests. Unfortunately, sustainable practices have not always been applied in the past, nor are they universally applied around the world today.

Architects, product designers, material specifiers, and homeowners are increasingly asking for building products that are certified to be from a sustainable source.For the forest products sector, the result of this demand has been the formation of forest certification programs. These programs not only ensure that the forest resource is harvested in a sustainable fashion but also that issues of biodiversity, habitat protection, and indigenous peoples rights are included in land management plans.

More than 50 different forest certification systems in the world today represent over 700 million acres of forest land and more than 15,000 companies marketing certified products. These programs represent about 8% of the global forest area and 13% of managed forests. From 2007 to 2008, the world’s certified forest area grew by nearly 8%. North America has certified more than one-third of its forests and Europe more than 50% of its forests; however, Africa and Asia have certified less than 0.1%

Approximately 80% to 90% of the world’s certified forests are located in the northern hemisphere, where two thirds of the world’s roundwood is produced. In North America, five major certification systems are used.

  • Forest Stewardship Council (FSC)
  • Sustainable Forestry Initiative (SFI)
  • American Tree Farm System (ATFS)
  • Canadian Standards Association (CSA)
  • Programme for the Endorsement of Forest Certification (PEFC) schemes.

In terms of acreage under certification, the FSC and the SFI dominate in the United States. These two systems evolved from different perspectives of sustainability. The FSC’s guidelines are geared more to preserver natural systems while allowing for careful harvest, whereas the SFI’s guidelines are aimed at encouraging fiber productivity while allowing for conservation of resources.

The growing trends in green building are helping drive certification in the construction market in the United States. Helpful online tools provide more information and data on forest certification, including the Forest Certification Resource Center and Forest Products Annual Market Review.

For more information, please see The Wood Handbook, Wood as an Engineering Material.

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.

Shiitake Mushrooms: A Commercial Forest Farming Enterprise

The following is re-posted from the USDA Blog. To read about FPL’s historic role in Shiitake cultivation, please click here.

By Kate MacFarland, USDA National Agroforestry Center, U.S. Forest Service

Workshop participants inoculate logs for forest grown shiitake mushroom production. (Photo credit: Ken Mudge / Cornell University and Allen Matthews / Chatham University)

Workshop participants inoculate logs for forest grown shiitake mushroom production. (Photo credit: Ken Mudge / Cornell University and Allen Matthews / Chatham University)

Helping landowners care for their forests and strengthen local economies is an important goal of the U.S. Forest Service, USDA National Agroforestry Center and their partnering organizations.

According to Ken Mudge of Cornell University, any farmer with a woodlot and the drive to diversify should consider forest-cultivated shiitake mushrooms. They are well suited to the increasing demand for locally produced, healthy foods.

With a retail price of $12 to $20 per pound, the demand for shiitakes is considerable throughout the Northeast. As an added benefit, growing mushrooms encourages landowners to learn more about managing their forests.

Using freshly cut logs of oak, beech, sugar maple, hornbeam or musclewood, Mudge says that a landowner with a solid production plan can grow one-half to one pound of mushrooms per log in two to three harvests each year for three to four years. Thus, he believes that forest cultivation of mushrooms not only produces delicious food, but is also one of the most reliably profitable non-timber forest products grown in a forest farming system.

Working with a number of partners, Mudge first held a shiitake inoculation workshop in 2009. Although it was unusually cold and icy, 40 people attended. Encouraged by this interest, Mudge and others applied for and received funding from USDA’s Sustainable Agriculture Research and Education (SARE) program to teach interested landowners how to start commercial-scale shiitake mushroom farming.

Workshop participants inoculate logs for forest grown shiitake mushroom production. (Photo credit: Ken Mudge / Cornell University and Allen Matthews / Chatham University)

Workshop participants inoculate logs for forest grown shiitake mushroom production. (Photo credit: Ken Mudge / Cornell University and Allen Matthews / Chatham University)

Unlike one-off workshops, this effort included hands-on training over two years in both the mechanics of growing shiitake mushrooms and how to start a shiitake farming enterprise. A total of 400 participants from eight states participated in the first year.

Since these initial workshops, a number of additional efforts have come about. Several farmer advisors from this project have gone on to successfully acquire SARE farmer grants to research key questions they confronted in their own shiitake operations. Mudge’s group also obtained USDA funds to diversify forest mushroom production by developing production methods and running on-farm trials of three other types of gourmet mushrooms: Lion’s Mane, Wine Cap and Maitake.

With funding from USDA, these creative scientists and farmers are providing strategic research and outreach to catalyze a forest-grown mushroom industry. The Cornell-lead project is currently working to educate farmers on methods of mushroom cultivation through the Cornell Small Farms Program.

New Technology, Old Problems: Heat Release Research an FPL Mainstay

The following post is adapted from the book Forest Products Laboratory 1910-2010, Celebrating A Century of Accomplishments.

As an early promoter of the use of heat release rate as a measure of relative flammability, John Brenden developed the original Forest Products Laboratory (FPL) apparatus to measure the heat released by a burning material in the 1960s. Heat release research was reliable and effective, and FPL continued to obtain new equipment as better technologies were developed to measure heat release rates.

The cone calorimeter replaced the apparatus from Ohio State University that was employed by FPL researchers in the 1980s.

In the 1980s, the original apparatus was replaced by one from Ohio State University, and 10 years later, was replaced by a cone calorimeter developed by the National Bureau of Standards. Today this organization is known as the National Institute for Standards and Technology. The cone calorimeter is used in investigations into fire-retardant treatments (FRT) for composite materials and fundamental research on the fire behavior of wood.

A cone calorimeter is a laboratory instrument that gathers data ranging from ignition time, to combustion products and, of course, heat release rate. It is used with small samples of flammable material. Its name reflects the conical shape of the radiant heater used in the device.

In addition to their use in evaluating the effectiveness of fire-retardant treatments, test methods for the rate of heat release were critical in the development of models to predict flame spread behavior of wood and times for flashover in the standard room-corner test.

Heat release graphs are still used by FPL researchers to determine the effectiveness of flame-retardant wood treatments.

Today, FPL researchers still use heat release rates to determine a material’s flammability. FPL Research General Engineer Mark Dietenberger, and Laura Hasburgh, a Fire Protection Engineer at FPL, feature an FRT heat release rate graph in their recently published document, Wood Products Thermal Degradation and Fire in the Materials Science and Materials Engineering Reference Module for Elsevier. More information can be viewed here.