An Easier Way to Timber Frame
A lot of people marvel at the strength and beauty of timber-framed buildings, with their exposed posts, beams and braces. But, despite admiration for this kind of work, few do-it-yourselfers consider using timber framing techniques to build their decks, verandas, sheds and workshops. This isn't surprising, for a number of good reasons: Few people have access to a sawmill that will cut the timbers for them; chopping out the huge mortise-and-tenon joints requires special tools; handling and raising large, green timbers is heavy work that demands a lot of hands; design information is difficult to find; and few building inspectors are familiar with the process.
These obstacles can, however, be overcome using a technique I 've come up with for a hybrid version of a timber frame wall that's more practical than the traditional version; With this approach, you'll be able to get strong,
Knee Braces and Hand Rails
Knee braces are the short, angled supports that extend diagonally between a post and beam. They add tremendous strength to a frame by preventing it from racking side-to-side. Structures like a veranda roof (which is fastened to an existing house) don't really need knee braces, but self-supporting structures like a garden shed or workshop do. Both knee braces and hand rails can be made from 3 x 5 mini-ties with curved edges used to make the walls of raised garden beds. Squaring the edges of a mini-tie will give you a better fit within posts and beams.
This part of my design differs the most from the traditional approach because the beam is made of multiple layers of nominal 2-inch-thick lumber bolted together and camouflaged to create the impression of a single, one-piece beam. Building a composite beam like this means you won't have to hoist a heavy, single-piece beam into place, and it's easier to make the mortises by leaving spaces or pockets between layers. This is a lot easier than drilling and chopping a traditional mortise in solid wood. Angled mortises for the knee braces can be made by cutting the pieces of 2-inch-thick lumber on an angle and leaving a gap between them during assembly.
To make a beam, bolt together four 2x8s with 1/2-inch x 6-inch galvanized carriage bolts staggered every 18. Be sure to inset the nuts and washers below the surface of the beam if you want to cap them. This is a typical beam size for many applications; 2 x 10s and 2 x 12s also make excellent beams. The exact distance such a beam can safely span depends on the total load exerted upon it. Your local building code includes tables that describe the various composite beam sizes permitted for specific spans.
The close-up end view illustration shows how routing the visible corners of the lumber before assembling the beam hides any alignment errors from one plank to the next.
Ready-cut solid-wood posts typically range in size from 4 x 4 to 8 x 8, or larger. Rectangular posts are available, but aren't typically stocked by lumberyards because of minimal demand. Most posts are made of pressure-treated softwood (the least expensive, most readily-available material around), but western cedar is also widely available. It may cost more, but it's easy to work with, resists warping and looks great. For hybrid timber framing applications, stick to 6x6s and 8x8s; 4x4s maybe strong enough in theory to hold up the roof of a small shed or a veranda, but they'll lose strength once you cut the pockets and tenons needed to interlock with the rest of the frame. Although green wood is used in traditional timber framing, I'd recommend dry posts for the hybrid version. These will cost a bit more, but are a great deal lighter and have likely warped as much as they're going to.
For typical jobs, each post will require two modifications: a tenon on the top end to fit into the beam and a pocket for the bottom end of the knee brace and the end of any hand rail you might include in your design.
To cut the tenon, use a circular saw and 1 bench chisel. Draw square layout lines on all four sides, all the way around the top of the post where the bottom edge of the beam will end. In the example shown here that area's labeled the tenon shoulder. Cut the shoulder first to a depth that will leave enough stock in the center of the post to form a tenon the exact thickness of the central part of your beam (in this case, 3). Continue to make similar cuts at the same depth, about 1/4-inch apart, all the way to the end of the tenon on all four sides. Use a chisel to remove the waste material from around the tenon.
The illustration shows angled knee braces extending between the horizontal beam and the post, plus a hand rail. These require pockets cut in the side of each post. To make the pocket, I use a large plunge router following a plywood pattern. You could also use a more traditional drill-and-chop method to make the pockets.
As you erect your posts and anchor their bases, you'll find it easier to install your knee braces and hand rails (if any) as you go. In fact, this is essential for a hand rail held in pockets between posts. As you add pieces of lumber to make up your beam, clamp the pieces together, wrestle them into alignment and drill bolt holes through all pieces at once. Stagger joints at least 3-feet between pieces of wood. Extra-long spade bits that bore completely through thick timbers can be ordered through any hardware store. The same bolts that hold the composite beam together also replace traditional wooden pegs for joining posts and beams together.