PolyIso necessary under metal roof in zone 4
I live in Portland, OR, which is region 4. We’re replacing our roof and highly considering a metal roof. The contractor included installing a layer of poly-iso under the metal roof as an option, but that would put us out of budget. The contractor put that as recommended, but not required, but I want to check how “not required” that really is.
We currently have r-50 cellulose insulation in the unfinished attic and have been told by energy efficiency contractors in the past that we have good ventilation as well. So I don’t know if everything is good given the attic, or if adding the poly-iso will be needed, or if we can skip the poly-iso, but install more ventilation to be safe.
Thanks.
Dan
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The metal roof, BTW, would have a cool roof certified paint/coating.
Assuming you HVAC is elsewhere, and since you have a vented attic with lots insulation on the floor, the polyiso above the roof deck won't do much. Since you have a lot of insulation there already, reducing your attic temperature a bit will barely budge your cooling load.
The polyiso above would only be needed if you are looking to converter to an unvented conditioned attic.
Thanks. There's return ducts up there, but that's it as far as HVAC goes (and they're also well insulated). So it sounds like we can skip the poly-iso. Thanks.