Gambrel Dogleg Splines

The second of the three (and counting, Jack?) remarkable Morway Projects was his four story apartment building in Cambridge, MA. The gambre; roof is covered in heavy slate. Gambrel roofs can be a structural nightmare, acting as five-pinned arches with the least provocation. Any more than three pins in any arch makes for a shifty mechanism; one that has to be held carefully in line. I used the ridge at this building as a lateral restraint against movement. It is a pentagon-shaped 10 x 14 on the flat. This ridge is intended to resist more lateral load than vertical – it also made for a ridge beam that was safer for “ridge dancing” as soon as it was up – just ask Jack’s magnificent and standard-setting-understanding spouse, Nancy. This ridge beam should be able to keep the gambrel roof from shifting from side to side, but we had to connect the upper rafters to the lower anyway, so why not add some suspenders to the ridge beam/belt? The rafters interconnect through “dogleg splines” shaped to the two roof slopes and made from high quality plywood. The peg patterns may not generate full moment capacity, but they surely made the roof more secure than all sorts of other joints I might have designed.

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