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Roofing insulation without attic

alex_gba | Posted in General Questions on

Hi all, I’m looking to redo the roof in the house I recently moved into in Redondo Beach, CA. It was built in the 70s with cathedral ceilings and exposed beams in almost all the rooms and almost no attention to insulation. It also doesn’t have any central heating or cooling, so on winter mornings it’s 50° inside and during summer it’s pushing 90°. It has both flat and pitched roof areas.


I’ve had a few people come out and give quotes, but they mainly do underlayment and cool shingles. I expect the shingles will help a bit with the heat in the summer, but it seems like above-deck insulation options could help even more. One contractor recommended a Low-E reflective insulation, but it seems like a lot of the benefit goes away without the ability to have an air gap and I’m not sure it’s meant to be installed under shingles.


Does anyone have recommendations on an approach here? I’d prefer to keep the interior beams as they are for now and just focus on the exterior. I’m curious if something like a Low-E Therma-Sheet that would add a small R value would make a noticeable difference, or if the only meaningful option would be to add a rigid insulation layer and more sheathing before the shingles. The weather is pretty moderate, mainly want to take the edge off.




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  1. user-2310254 | | #1


    If you need a new roof and may be considering adding an HVAC system, I would consider installing rigid foam above the sheathing. (See Using reclaimed foam can reduce your materials cost quite a bit.

    Note that insulating cathedral ceilings requires particular care. See

    From your photos, it also looks like you have some areas with a low slope. So you may want to read to learn more about your options for installing insulation and avoiding potential problems.

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