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Firewall for the North wall of loft » Our Sustainable Home
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Firewall for the North wall of loft

July 8th, 2009

Just before going on strike our inspector indicated he wanted the North wall of the loft area to have a 45 minute fire assembly. (The loft is singled out since it is a stick-frame construction, not ICF like the rest of the house.)

Any walls of a house that face a neighbouring property (at a close distance) need to have a 45 minute fire rating, but this is usually just for fire that would occur inside the house. As such, putting 5/8″ drywall on those walls is sufficient.

But (as I understand it) a “45 minute assembly” needs to have that rating on EVERY side of the wall (top and bottom, too). Because we didn’t have a good way to do this, we were looking at having to drop our cool soya-based spray-foam insulation from the north wall, and use Roxul.

Roxul is a great product but it doesn’t provide the air-seal that spray-foam does. This morning, *just* before the drywall was to go up, the fellow from Ryerson who is researching our house called to say he had an engineer who could give us a letter describing a fire assembly to satisfy the city requirements!

A flurry of phone calls later, it looks like our friends at Foam Comforts can come back tomorrow to complete the air-tight seal we’d been hoping for in the loft! This is another one of those: it now feels ‘right’ moments. And more importantly the house temperature will ‘feel right’ too!

The loft area uses 4.5″ of foam (R-31) insulation on the roof and walls.

The solution, by the way, is quite simple: We just need to put 5/8″ drywall (probably concrete board for moisture protection) on the outside of the house as well. Our builder was very worried about the spray foam carrying a fire through the wall, but since each 5/8″ sheet provides 45 minutes, the flammability of the inside of the wall can be discarded (assuming it isn’t an accelerant, which I don’t think it is). Then we just add our ULC-rated cladding (hardieboard, in this case) to the outside of the house and we’re good to go!

Good save, team! 🙂

Posted by Colin
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