Roof insulation – 1/2″ EPS worth it?
Hi Everyone,
I posted earlier about this roof assembly, but a different question this time around.
California Zone 3 climate zone.
We’re doing a metal roof, with R-38 spray foam on the underside of the roof deck. Our roofer is recommending 1/2 EPS foam on TOP of the roof. Why is unclear. He says it might help smooth out the sheeting…or help with insulation…or perform some magic 🙂
From an energy perspective, is there any material value in laying down 1/2″ of EPS, at an R-Value of ~2? I guess I could say I get an R-40 roof now?!!
I asked my manual-j rater to update and see what happens, and he just changed the roof insulation from R-38 to R-40, and it lowered our BTU requirements by ~500BTU.
$6,800 dollars for the upgrade. Feels like I should spend my money elsewhere.
Am I missing any other energy savings value? Would the 1/2″ help create any materially beneficial thermal break between the metal roof and the spray foam?
Thanks for your ideas and advice!
Matt
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Replies
Is it to late to change your plans?
Spray foam is a mistake in new construction! It is the most expensive and least green way to buy r value.
Consider taking the time to plan an HVAC system that can be located below the ceiling inside the conditioned space and covering the attic floor with cheap fluffy insulation.
Walta
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