Build a Home for $10,000 in 10 Days!
(Page 2 of 3)
February/March 2009
By Chris McClellan
Many timber framers mill timbers flat and square on all sides. Timbers trimmed square and straight are easier to work with, especially when it comes to cutting joints or attaching sheathing to the outside of the timber frame. The downside is that square-timber framing usually requires expensive woods, such as white oak, that are dimensionally stable and don’t tend to twist as they dry.
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Castle has found a compromise that gives him the benefits of both techniques — a kind of “three-quarter-round timber frame.” He simplifies his cutting and fitting by milling one or two sides of each log flat, but he leaves the other sides “in the round,” which keeps the wood stronger and less likely to twist. This allows him to use smaller trees of non-premium species, even with minimal drying.
A three-quarter-round timber-frame is assembled with flat sides of the wood facing out, making it easy to square and plumb the sides of the building. Milling only the surfaces of the wood that will be covered by the building sheathing also saves one-half to three-quarters of the milling time, while retaining the rustic beauty of the round wood where you can see it on the interior walls.
The system of joinery Castle has developed to work with his three-quarter-round timbers is quick, easy and forgiving. He starts by squaring the round wood at the location of the joint with a radial arm saw and a chisel. A chain saw will do the job a lot quicker, but the visual quality of the joint suffers.
Squaring the timber at the joints makes it easier to lay out cross pieces and knee braces. The resulting edge between the round and square portions of the timber also wedges the wood together in a way that adds strength to the joint. The connection is secured by countersinking one or two half-inch lag screws through the “meat” of both timbers. (See the Image Gallery.)
The flat surfaces of the three-quarter-round timber frame also make it easier to attach sheathing and roofing with a minimum of cutting and fitting. Castle usually sheathes his buildings with a “sandwich” of rough-sawn boards around a core of 2 inches to 4 inches of foam insulation, making these buildings extremely tight and well-insulated. (See Castle House Diagram.)
More Tips for the Technique
It is worth noting that designing a building on a 4-foot-by-8-foot module (open space between timbers of 4-feet-by-8-feet on center) has a number of benefits. First, the timber frame will cover most, if not all, of the joints if you choose to use drywall as the interior layer of your sheathing sandwich, saving time in the finishing process. The drywall even can be painted before it is hung, with no taping or masking!
