I am self-building a 20×22 workshop. Half the roof is a 14in12 gable; the other half is a 7in12 shed. According to the code tables, all I require is 2×6 24oc for both. However, with allowance for venting, 2×6 rafters will not even give me the R20 that 2×6 walls could. QUESTION: what is the most efficient way to increase the depth of insulation on both roofs?
– Go 2×10 for all rafters?
– Fur out the inside (outside?) with 2×4 utility lumber?
-Sheath the inside (outside?) with rigid foam?
I live in mid-northern Canada and although good old global warming means it is unlikely we will ever see a bitter -40 for weeks at a time again, I still want to minimize my gas bill.
Replies
It's a shop? Why would you want to vent the roof?
What kind of snow load are you designing too?
2x6@24" sounds kinda shakey to me.
Go with 2x10s & blow it with dense pack cells & you'll be toasty plus as an added bonus it won't collapse some day when Global Warming decides to dump 3' of wet snow on it.
Joe H
Snow load is 40PSF. I thought under sheathing vetilation was an absolute requirement regardlass of purpose.
It's required for living space because living people create moisture in the air. Aspiration, showers, cooking, etc.if you will be working wwith a lot of green lumber drying, or spraying a lot of water based finishes, maybe venting is a good idea, byut generally, a shop has doors and windows open quite often and is not heated as much as a living space so it doesn't drive the moisture up as much.
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