BCade
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Hey Folks,
I’m hoping to get some help understanding the venting/insulation requirements for a low slope prescriptive roof, specifically R806.5.5.1.4 and if it could be used in a mild climate to eliminate the need for rigid or impermeable insulation in the assembly.
FWIW I’m in California but it seems to be the same as the 2018 IRC other than replacing national climate zones with its own. https://up.codes/viewer/california/irc-2018/chapter/8/roof-ceiling-construction#table_R806.5
It states:
I can’t seem to find an example of how to calculate this, for instance what source is used for calculating the outside average air temps and is it specific to the site or just an average of our climate zone?
With my city's coldest month’s average low at 43° and high at 61° It seems like the sheathing would average above 45° on its own, so could I infer that to mean I would be okay with zero inches of external insulation?
It does not specify whether it applies to air permeable or impermeable insulation, so would there be anything else preventing the use of dense pack cellulose in this assembly?
Then for a bonus question, with a radiant barrier being required in the prescriptive energy path, where would I put it? Without an air gap it does nothing on the underside of the sheathing, so that leaves the top of the sheathing, utilizing the air gap under the standing seam roof. If anyone has a suggested product/approach I’d love to hear it.
Thanks, and for reference, below is the assembly I'm working on (note that it doesn't show the 2x10 rafters)
I’m hoping to get some help understanding the venting/insulation requirements for a low slope prescriptive roof, specifically R806.5.5.1.4 and if it could be used in a mild climate to eliminate the need for rigid or impermeable insulation in the assembly.
FWIW I’m in California but it seems to be the same as the 2018 IRC other than replacing national climate zones with its own. https://up.codes/viewer/california/irc-2018/chapter/8/roof-ceiling-construction#table_R806.5
It states:
I can’t seem to find an example of how to calculate this, for instance what source is used for calculating the outside average air temps and is it specific to the site or just an average of our climate zone?
With my city's coldest month’s average low at 43° and high at 61° It seems like the sheathing would average above 45° on its own, so could I infer that to mean I would be okay with zero inches of external insulation?
It does not specify whether it applies to air permeable or impermeable insulation, so would there be anything else preventing the use of dense pack cellulose in this assembly?
Then for a bonus question, with a radiant barrier being required in the prescriptive energy path, where would I put it? Without an air gap it does nothing on the underside of the sheathing, so that leaves the top of the sheathing, utilizing the air gap under the standing seam roof. If anyone has a suggested product/approach I’d love to hear it.
Thanks, and for reference, below is the assembly I'm working on (note that it doesn't show the 2x10 rafters)