The Super-simple Gambrel Roof
Anyone who's seen any of rural America has seen a gambrel roof. These simple but elegant structures (which, until not too long ago, were the hallmark of the American farm) have been popular on hay barns for many years, primarily because the loft of a barn topped with such a roof will hold a considerable amount of hay. There's no reason, though, why the classic gambrel cannot be used on other kinds of structures (such as log cabins) when storage space is at a premium.
March/April 1977
By Philip Baechler
A couple years ago, when I was building my 15' x 20' log cabin in far northern Washington, I decided to top the building with a gambrel (rather than a more conventional gable or A-frame) roof. Not only would the gambrel's steep side pitch give the cabin ample upstairs room, I reasoned, but the double-sloping design would make more efficient use of roofing materials than a giant A frame ever could. And besides that, I like the looks of gambrel roofs.
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Some background reading soon taught me, however, that a conventional barn-sized gambrel is a nightmare of purlin beams, ridge beams and dovetail joints. What I had in mind, in other words, was a fine project for an army of engineers, but one that was probably beyond the capabilities of two non-professionals (such as Jim—my building partner—and myself).
Rather than give up, however, I decided to try to simplify the construction of the gambrel I wanted. What I ultimately devised was an easy-to-work-with system of lightweight trusses that could be built flat on the ground, then erected atop the cabin and covered with exterior plywood to give the barn-like roof shown in the accompanying photos. Here, briefly, is how the trusses (and the gambrel roof formed from them) went together:
RESEARCH AND PLANNING
I'd planned to start by making a dozen or so gambrel-shaped frames or trusses out of 2 x 6 lumber. Initially, though, I had no idea how I could connect the pieces of each truss together so that they'd be held rigidly in the proper configuration.
Then I remembered reading about a system of plywood straps that someone had used in building a geodesic dome. I say "straps" but, actually, they were nothing more than wooden brackets nailed to the sides of two connecting beams to hold them (the beams) together. These plywood brackets were just what Jim and I needed to give our roofing trusses adequate rigidity.
Next we sat down and made scale drawings of several gambrel roof designs, each one employing a different combination of side slopes. In the end, we settled on a roof plan that looked good, made efficient use of materials, and allowed for porch and eave overhangs.
LAYOUT AND CUTTING
At this point, we measured and cut our truss lumber. First, we made a full-size layout of our gambrel on smooth, level ground and drove stakes into the earth to mark the locations of the four rafters in each truss. Then we laid four 2 x 6 beams out flat in their proper positions and—using a string line—marked the correct lengths and angles to cut them. Next, we sawed the pieces of the first truss to length, set them down between the stakes again, and (after carefully checking their fit) used these original 2 x 6's as patterns with which to mark and cut the rafters for the remaining trusses.
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