Framed-in-place roof
To maximize the storage space under the roof—and for a more pleasant interior—I framed the roof in place with rafters instead of hoisting trusses into position. Getting the roof started was tricky, but once I had the ridge board in place with a couple of temporary supports, the going was easy. I raised the ridge board by tacking it to a couple of lengths of 2x4 and temporarily clamping it in place. I cut one rafter from a straight 2x6 to use a guide.
The rafter angles are easy to determine on a 12:12 pitched roof. I cut the end that meets the ridge at 45° and trimmed the resulting point so that it wouldn’t interfere with the roof sheathing later. Next, I cut the rafter tail to 90° to simplify the trim work. A "bird’s mouth" notch is needed to fit the rafter tail onto the top plate of the wall, so I cut one, then test-fit the rafter in position. Once it fit correctly, I used this rafter as a template for cutting the rest.
To install the rafters safely, I laid a few 2x6s across the top plates of the walls to use as a temporary scaffold, then installed the rafters from one end to the other. When the walls are plumb and square, the identical rafters will ensure that the ridge board is perfectly centred on the building. To complete the roof framing, I installed rafter braces on each gable end of the building.
Sheath, vent and shingles
I chose 5/8" plywood to sheath the roof, attached with ring-shanked nails. You might prefer solid pine boards for a more rustic look. To allow for the continuous roof vent, I stopped the roof sheathing one inch short of the ridge on each side of the roof. Next, I installed aluminum drip edges on the eaves and gable ends, followed by 20-lb. roofing felt, which I used from the eaves up to the ridge. Standard asphalt shingles are the most economical roofing material, but smaller buildings afford the luxury of using more expensive materials, such as cedar shakes or metal. Installing shingles on a building this size doesn't take long. I set up scaffolding to reach the first courses of shingles without having to perch on the roof. After the first few courses, I installed a couple of roof jacks and a plank to complete the rest of the shingling. When the shingles were complete up to the ridge, I unrolled a continuous polyester roof vent out along the ridge and tacked it into position with roofing nails. The ridge cap shingles were cut from full size into thirds, with a taper on the non-exposed portion of the shingles. I bent these cap shingles over the ridge vent and secured them with roofing nails. These nails need to be longer to accommodate the additional thickness of the vent material. It's smart to install the ridge cap shingles so that the overlapping edges face away from prevailing winds.
The continuous ridge vent I chose, Cobra Vent, is more expensive than other options, but the huge vent area means that the large space under the 12:12 pitched roof stays reasonably cool in summer. The Cobra Vent should keep insects out, important if your cottage is in a mosquito zone like mine.
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