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Old 09-15-2020, 09:24 AM   #1
Join Date: Sep 2020
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Flat roof insulation question

My house is mid-century modern, built in 1956. Hot dry climate (So Cal desert). Flat foam roof with a 36"x8" vent at each end (gable vents?)

There is an 18" air space between the drywall ceiling and the underside of the roof deck. I guess technically, this is my attic.

The only insulation is layed out on the floor of this attic. It's marked "ALFOIL." It's basically an aluminum blanket - kraft paper on the bottom, an asphalt-coated piece of kraft paper in the middle, and a layer of aluminum foil on top. It's labeled as "reflective insulation." I think it's from the 1950s or 1960s.

That's it, nothing else. All the rafters and underside of the deck are bare wood.

I took the vents off from the outside to clean them, and noticed that the insulation is in fairly decent shape for being so old. The only bad parts I could see were the areas right behind the vents. I think wind blown rain got to those areas, so I ripped that material out (48"x16").

They don't make this kind of insulation any more, so what should I put in its place?

Would rigid foam boards work? Eps, xps or poly? I guess that kraft faced fiberglass is a bad idea, because it would be subject to wind blown rain through the vent (although, very little rain here).

The big box stores have a product that is a reflective foil insulation (bubble wrap with each side covered in foil), but they recommend not to install on the floor of an attic (only on rafters or underside of deck).

What if I just leave the area bare?

I only want to install something on the attic floor within arms reach.

Don't have the finances to properly insulate the entire roof right now, so any cheap solution would work.
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Old 09-15-2020, 02:11 PM   #2
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Re: Flat roof insulation question

The best time to re engineer the venting and insulation will be the next time you need a new roof.
I would insulate that section with what ever is at least equal to what you took out and then

I would have a sheet metal shop build a hopper for the bottom half of the vent holes that would catch the water and drain it to the outside of the siding.
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