Attic & Foam Insulation The Radiant Barrier Guru

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Hi there, I am just about to re-roof due to hail damage and my roofer has recommended a solar shield material to go under the one area of my roof where I see a large rectangular frost patch on cold mornings (this is above the cathedral ceilings). Though not functioning as a radient barrier will this help prevent the heat from seeping out. Is it safe for the shingles? Is it worth the extra expense? Thank you for you help.

Ed — would it be efficient to not only put foil on my roof rafters, but also over my insulation on the attic floor? -Kent

I live outside Phoenix, AZ and I have a flat roof that will be redone (no attic). Can I create a sandwich of plywood decking with foam spacers and then have a spray foam insulation installed on top?

We have a multi-level flat roof house with standard roofing material. Several rooms are VERY HOT (the same temp as outside or even hotter) despite using window tinting, solar shades and drapes. We live in Sedona, AZ where in the summer it will be in the mid-high 90’s at it’s worst and drop down to the 70’s at night. The MBR is a particular problem at the highest point of the house. It’s well over 85 in there even when it is only 80 outside. We have been told that is we «foamed» the roof using either R-7 or R-14 we would see a huge decrease in this heat issue and perhaps cut our very high electric bills in 1/2. The foam (depending on R-7 or R-14 and if we do the whole house or only certain rooms) was quoted at basically $2 a square foot. If it paid for itself in a couple of years or less then that would be fine. So thoughts? Is it worth doing this? We can’t insulate anywhere else as there is only a crawl space available since it is flat roof (and there is the standard pink insulation in there, I saw it when I had to take down a ceiling speaker). Thanks!

Rating: +0

I have a flat roof in rowhome in Philadelphia. I’m in the middle of the block. My joists run parallel to the front/back walls, so there’s no way I can vent. I need both a radiant barrier and insulation. Does the air space need to actually vent anywhere? Could I put up the foil with an air gap and then put fiberglass below? Fortunately I have full access to the underside of the roof deck. Thanks! Mike

Have you had a chance to take a look at the video: How to Install Radiant Barrier in a Cathedral Ceiling. It’s the third video on the page and it explains how you can get both a radiant barrier AND traditional insulation in the wall assembly for maximum benefit.

Rating: +1

I have a almost flat roof with no attic. Just the 4×6 beams then the ceiling and roof. How do I best improve insulation?

The downside is that there is no easy/simple way to add radiant barrier to a finished cathedral ceiling. The good news is that you do have a few options:

First, you could remove the sheetrock and install radiant barrier foil via the Cathedral Ceiling Method. This can be labor intensive and costly, but this would garner the best results.

Essentially your layers will be as so, coming from the roof down:

Roof deck

Air Space


Or, another option is to install radiant barrier foil over the existing sheetrock. but then you have to create an airspace. The best way to do this would be to use wooden battens over the existing layer of sheetrock and then staple the foil to the battens and then install new sheetrock over it. If you wanted to keep it simple, you could just bulk up what existing insulation you have. I recommend you get 3/4″ to 1.5″ foam board and apply it directly over the existing ceiling and the drywall over the foam board.

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Hi — We are building our entire home without any attic space. We have already bought one sided radiant OSB, 4cm polystyrene insulation, plasterboard, asphalt felting and shingles! The roof structure is of galvanized metal. What is the best way to construct our roof — we are in hot climate. Thanks for your advice.

If you are converting the attic space into living space that will be heated and cooled, then you will add insulation via the Cathedral Ceiling Method ; essentially since you have foil on the deck already, your layers will look like this coming down into the space:

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