Two bents
Last Spring Bob and I built a small 6' x 8' shed for a preschool in Ann Arbor. We had harvested some spruce the previous winter, and had had it sawn into various-sized timbers and boards. Using 4 x 4s for the main posts and beams, we prefabricated a simple timber-frame. The photo to the left shows the side wall framing, traditionally referred to as "bents" just after being erected. These include diagonal braces for strength and horizontal "girts" to provide a nailing surface for the siding.
Top beams on
The bents, having been fixed to the floor framing with stub tenons, were then joined together with two top beams. These were also braced at both ends, with door posts and girts added at the same time. In traditional timber framing all parts of the frame are joined with mortise and tenon joints, and secured with wooden pins. The budget for this project precluded our using this time-consuming method of joinery, but we did use a variety of lap joints which allowed the various pieces to "nest" together, securing each of the components of the frame with lag bolts and washers.
Partly sided
Five prefabricated roof trusses were then secured to the top beams, 24" apart. Again, we used simple lap joints to build these sturdy trusses, three of these being reinforced with collar ties. The photo at left shows the completed frame with roof sheathing attached, and partly sided. The siding itself was also spruce (from the same tree as the framing), in widths ranging from 6 to 12 inches, which we shiplapped and nailed vertically to the frame.
Satisfied customers
We finished up with a minimal amount of trim and topped the roof with standard three-tab fiberglass shingles. The door was built with the same shiplapped spruce with which we had sided the shed, and completed with a wooden handle and latch. The program directors pronounced themselves highly satisfied with the results, and it serves as storage for the preschooler's playground equipment.
But why a timber-framed shed? Certainly standard 2 x 4 frame construction is easier, the materials more readily available, and the skill set required less extensive. All of this is true, yet I have several reasons for preferring this method of traditional building over its modern cousin. Assuming a 24 inch-on-center (OC) construction (acceptable for such a small structure) the standard method of frame construction in this case uses 14.6% more lumber (this comparison only applies to the frame - the siding, roofing, etc. require the same amount of material in either method). If one opts to use 16" OC walls, that difference jumps to 18.5%. Using less of any resource is, in my mind, the right thing to do. But lumber is cheap, right, and time is money. True enough, but the timber-frame is much more rigid, and arguably stronger, than standard construction. Also, all of the frame members were actual size, so a 4 x 4 is really 4" x 4". This means less energy used in processing the lumber, and marginally greater strength. Furthermore, I built all the components of the frame in the comfort of my shop, fitting all of the pieces together, ensuring that everything was square, marking the material and pre-drilling holes for hardware as I went, to make it easier to reassemble. On the site Bob and I simply put the pieces back together and secured them with the lag bolts we had brought for that purpose. As the frame went together on site it proved to be level and plumb. The result was a relatively lightweight but strong structure, using less material and energy overall, and built largely with locally sourced materials.
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