Project Planning Guide
Visit the other sections of the Product Planning Guide for detailed information on the process of building a timber frame and valuable tips to consider as you get going.
"Mortise and Tenon Joint": The mortise and tenon joint has been used for thousands of years by woodworkers around the world to join pieces of wood, mainly when the adjoining pieces connect at an angle of 90°. In its basic form it is both simple and strong. Although there are many joint variations, the basic mortise and tenon comprises two components: the mortise hole and the tenon. The tenon, formed on the end of a member generally referred to as a rail, is inserted into a square or rectangular hole cut into the corresponding member. The tenon is cut to fit the mortise hole exactly and usually has shoulders that seat when the joint fully enters the mortise hole. The joint may be glued, pinned, or wedged to lock it in place.
Each timber frame is as unique as the individuals who select its design, and the Cabin Creek team is skilled and ready to guide you through the process of planning the structural details for your project. A timber frame can be customized to meet a variety of needs, including cost, appearance, and construction type.
Style of Timber Frame
At its heart, timber framing is about the use of large timbers to frame a structure instead of smaller dimensional (1-2” thick) lumber. However, making the choice to use timber is just the start of the design process because many styles of timber framing have evolved over time. Each style can result in a range of costs based on the complexity of the design. Below are descriptions of some of the styles and terminology.
- Mortise and Tenon Joinery. This is the time-tested basis of timber framing joinery. A hole or mortise (perhaps 2”wide x 6” long x 4”deep) is cut into a timber, and a matching tongue or tenon is placed in the hole and pegged with a wooden nail or peg.
- Bent Construction. Bents are 2D arrays of timbers usually joined with mortise and tenon joints. They can be described as a truss with legs. Multiple bents add to the length of a building. Bents are usually connected to each other with ridge timbers, purlins (horizontal timbers joining two principal rafters), and plates (horizontal timbers at the eaves or springpoints) to form a 3D structure.
- Post and Plate. A 3D structure with repeating common rafters usually supported at the upper 1/3 of the rafter by a long longitudinal plate.
- Post and Beam. In most of the US except New England, this is a timber frame made by butting timbers together and connecting them with metal plates and bolts.
- Compound Joinery. This is a more complicated joint due to unusual angles created by a roof plane meeting another roof plane in a perpendicular or oblique angle as would be seen where a main roof intersects another roof and forms a hip or valley.
If you are interested in seeing different styles of timber framing, visit us. We can show you examples of each of the methods described above in our office and model home.
Species of Timber
The other crucial factor in the structural design of your timber frame is the choice of wood. Throughout the years, Cabin Creek Timber frames has worked with a broad range of species such as Douglas Fir, Eastern white pine, cypress, white oak, Southern yellow pine, Western red cedar, and Canadian hemlock. The species of wood you select will have a significant impact on the cost, aesthetic, and structural properties of the frame, and Cabin Creek can work with you to help make the optimal choice.
The majority of our timber frames are cut of Eastern white pine. This species of wood is readily available in our area (lower shipping cost), and our experience shows that it is less expensive and more stable than most other species, showing less shrinkage, checking, and twisting over time. It can vary in color from bright white to cream when freshly cut, growing into a golden honey color within a few years.
We are sometimes asked if timber should be dried prior to building the timber frame. While Cabin Creek Timber Frames can arrange for timbers to be dried, we do not believe it is necessary to the process of building a timber frame. Unless there is a specific reason for the extra strength of dried timber or there is a hope that the wood will not check, it is usually a waste of money to have timbers dried. To control costs and achieve excellent performance, it makes more sense to design the frame to carry the loads adequately when green. As timbers dry, there is always some checking and shrinking, but the timbers grow 25% stronger as they dry and shrink 4-8% across the grain. With timber framing, this shrinkage is not important, since we depend mostly on the length of timbers. Shrinkage in this direction-lengthwise-is 0.1% to 0.2%, which is negligible.
The story behind radio frequency drying of timbers starts with some history. Timber frames have been built for some 2000 years, and many of these buildings are still in use after centuries. In each of these buildings, green timbers were used and allowed to dry slowly in place, held by their neighboring timbers, with minimal checking and damage to the timbers. About 100 years ago, after western forests began being logged and lumber from them shipped east, kilns started being used to dry dimensional lumber ( 3” and less) so that rail car loads weighed much less and the locomotives could handle more lumber. Attempts to dry large timbers (5” or more) did not work well then and still do not work well.
Checking occurs more rapidly and often. It is possible to dry the outer 1½” but the inner sections stay green or wet. Air drying usually requires about one year per inch of depth, but most people do not want to wait 6-8 years for this. Recently, radio frequency kilns (or microwave ovens) have been used to dry timbers to the center of the timber. There are very few facilities in North America (maybe 3 or 4) which can do this, and they add considerably to the cost of the wood—the cost of drying and shipping. Planing is usually done last to insure perpendicular sides, resulting in higher costs.