For Timber-Frame Construction, Look for Reclaimed Materials
The big-boned house
Compared to stick framing, timber framing uses larger pieces of wood, with wider spacing between members. In a traditional timber frame, the vertical posts are joined to the horizontal beams with mortise-and-tenon joints and wooden pegs. The structural network of timbers in a wall or truss that makes up one cross-sectional part of a timber frame is called a bent.
Whether timber framing is green depends on the philosophy of the builder, where the materials originated, the logging practices used to procure the materials, and the durability of the finished home.
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This big frame can accommodate a variety of wood species
Timber frames can be built from eastern white pine, long-leaf pine, cypress, Douglas fir, northern red oak, white oak, and many other species. Some timber framers specialize in reusing beams from demolished buildings to construct a new house.
The size of the timbers depends upon structural and aesthetic requirements, but 8x8 and 10x10 are typical sizes.
People care for attractive homes
Reusing old timber frames isn't just resource efficient. Old hand-hewn and rough-sawn structures have an aesthetic that appeals to a wide range of people, whether or not they prefer modern or traditional architecture. Part of the value is that attractive, timeless buildings are typically better cared for than mediocre ones. Some people are lucky enough to find old barns that can be shored up and refitted right where they stand. Often, however, a frame will be stripped, dismantled, and stored until it can be recycled into the skeleton of a new structure. Removing historical structures from their original sites brings up some concerns, but many of the barns, mills, and warehouses that are salvaged would be destined to fall on their own if they were not claimed by well-meaning builders.
New frames have their benefits. A custom-built timber frame will offer more design flexibility. In fact, new frames have unlimited potential for shapes and textures. Starting from scratch might also make it easier to address efficient space planning and ideal sun exposure. The open spaces and the warm, strong look of exposed timbers are likely the main attractions in these homes.
A timber-frame roof on conventional walls
Clients sometimes request an exposed timber-frame roof for a great room in a conventionally framed house. To keep costs down, timber-framed roof trusses can be placed on conventionally framed walls. Such roofs typically have purlins that are 4 feet on center; the tongue-and-groove (T&G) ceiling boards are installed on top of the purlins perpendicular to the ridge. Several layers of rigid foam insulation go on top of the T&G boards, followed by eave-to-ridge 2x4s for a vent channel and oriented strand board or plywood roof sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. .
You must check with your local code official
Currently there are no prescriptive design guidelines in the IRCInternational Residential Code. The one- and two-family dwelling model building code copyrighted by the International Code Council. The IRC is meant to be a stand-alone code compatible with the three national building codes—the Building Officials and Code Administrators (BOCA) National code, the Southern Building Code Congress International (SBCCI) code and the International Conference of Building Officials (ICBO) code. for timber-frame construction, so a local code official may require that an engineer or architect sign off on the design. Timber framers typically have relationships with local architects and engineers who are familiar with timber frame construction and can help with design and code-approval issues. Some timber framers have these services available in-house.
ABOUT TIMBER FRAMING
A time-honored building method
Timber framing, also known as post-and-beam construction, is an ancient building method that is more expensive than conventional stick framing. Still, it is appealing on several levels. A frame of recycled timbers covered with SIPs can make a great-looking house that's also green.
MORE ABOUT TIMBER FRAMING
Modern building codes may require the use of some metal connectors in a timber frame, but the construction essentially relies on traditional methods of joinery, such as dovetail and mortise-and-tenon joints, that are inherently strong and stable. Houses can be designed so that some or most of the frame is exposed, making interiors warm and inviting.
Advantages of an open floor plan without bearing partitions
It isn't just the look of attractive timbers that can make a space more comfortable. With smart window placement, the openness of a typical timber frame can let in plenty of sunlight, giving great opportunities for daylightingUse of sunlight for daytime lighting needs. Daylighting strategies include solar orientation of windows as well as the use of skylights, clerestory windows, solar tubes, reflective surfaces, and interior glazing to allow light to move through a structure. and passive solar heating.
Large timbers allow generous clear-spans without the need for many, if any, interior bearing walls. This makes interior spaces easier to rearrange as the needs of the building’s occupants change.
Timber frames work well with SIPs
Another design option, the use of structural insulated panels (SIPs) as exterior walls, creates a tight, well-insulated building envelopeExterior components of a house that provide protection from colder (and warmer) outdoor temperatures and precipitation; includes the house foundation, framed exterior walls, roof or ceiling, and insulation, and air sealing materials. and gives timber-frame buildings a performance edge over standard stick-frame homes. Using SIPs to wrap the timber frame also places the frame within the conditioned spaceInsulated, air-sealed part of a building that is actively heated and/or cooled for occupant comfort. , stabilizing it from the effects of temperature and humidity swings. Straw bales, cob, and leichtlehm are some less conventional wall materials that work well if detailed properly. Factors to consider when choosing infill materials include local availability, desired wall thickness (straw bales produce very thick walls), and the availability of skilled labor.
Big timbers come from big trees, so choose wisely
Unfortunately, timber framing uses a resource that is increasingly precious. Large, old-growth trees understandably make the most desirable frames, but this is exactly the lumber that can’t be harvested sustainably. There are at least three other options:
- Chuck Bickford/Fine Homebuilding #166
- Roe A. Osborn/Fine Homebuilding #180