Hello,

I’m looking for help with a roof I am designing. The cottage is in Muskoka in Ontario, Climate Zone 6 with a lot of snow each winter. The roof has been leaking over the winter. There was a lot of ice damning, and it continued to leak in the rain after the snow was gone. It was built in 1976 with a cathedral roof. The previous owners did a hack job of the roof (exposed nails, 3rd layer of shingles that didn’t go below the poor ridge vent, poor flashing, etc). Oh, and the previous owners had ice-melting cables installed on the roof, but they were actually melting ice at the top of the slope and didn’t have a lot of cables at the bottom after the wall edge! We haven’t yet ripped up the roofing and sheathing to see how much damage there is. Hopefully, the rafters are still in good shape. I’m not even sure if they are 2×10 or 2×12 rafters on Heavy Timber beams (4×14?). The roof is also only a 3:12 slope.

I would like to remediate this roof without impacting the interior. That is, I want to leave the rafters and the gypsum bd ceiling. Remove the shingles, membranes, sheathing and insulation, treat for mold, etc if there is any, and build a new roof on the existing structure.

I have worked out a detail (attached) that I hope will work in providing a R51 Roof assembly. I’m just not sure if it works and if it is buildable. Will I have to fight with the contractor to get it built this way? Will it pass code? 

The struggle between vented and non-vented is difficult to figure out and what should be breathable from which side or if it should just be sealed up completely? 

Do I need to keep at least 2/3 of the R value above the sheathing and less than 1/3 below? I have achieved that with this detail (R36 above, R15 below).

Please let me know what you think. I’m hoping to submit for building permit in a day or two.

Thanks in advance.

Maurey