I’m starting to look into building a new house and I’m stuck on insulation.

Right now, I’ve got Rockwool in the walls and cellulose in the attic (17 year old house), but I keep hearing mixed reviews on spray foam — especially for our climate down here in South Louisiana.

If you were building today, what would you go with?

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Posted by Civildawg

Member since May 2012

10312 posts

Posted on 1/8/26 at 8:23 am to Will Cover

I'm in the process of retrofitting insulation in my attic. I would go cellulose based on my research, BUT the more important thing would be to airseal the top plates and drill outs in the attic space before you put in insulation. It will be much easier to airseal now

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Posted by LS(DB)U

Louisiana

Member since Aug 2012

214 posts

Posted on 1/9/26 at 1:19 am to Will Cover

Open Cell Foam at roofline

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Posted by Will Cover

Davidson, NC

Member since Mar 2007

39998 posts

Posted on 1/9/26 at 6:20 am to LS(DB)U

quote:
Open Cell Foam at roofline

I read this, after googling your suggestion. Here's what their AI came up with:

quote:
Using open-cell foam at the roofline creates an air-sealed, conditioned attic, which is cost-effective and excellent for sound dampening, but it's vapor-permeable, allowing moisture to pass through, which requires careful management, especially in humid climates or with metal roofs, to prevent sheathing issues; while good for leak detection (water shows through), closed-cell foam offers superior moisture resistance and R-value per inch but at a higher cost, making the choice dependent on budget, climate, and building goals, often paired with proper ventilation or vapor barriers as needed.

I don't plan on having a metal roof, or if I do, it will be very minimal as more of a decorative piece, perhaps over the front porch area, but this all depends on the design of my house, and look I am trying to accomplish (still to be determined).

My initial thoughts were to have a radiant barrier at a minimum. Can open-cell foam be sprayed on top of a radiant barrier, or is this even necessary?

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Posted by good_2_geaux

Member since Feb 2015

799 posts

Posted on 1/9/26 at 7:53 am to Will Cover

I’ve never heard of radiant barrier then spray foam over the radiant barrier (but maybe I’ll learn something new on here).

Another thing to consider is the roof shingle manufacturers warranty. I only am aware of one shingle company (Certainteed) who allows a spray foamed deck in their warranty.

Personally, I like a radiant barrier only under the plywood deck in the attic.

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Posted by Citica8

Duckroost, LA

Member since Dec 2012

3951 posts

Posted on 1/9/26 at 9:27 pm to Will Cover

quote:
Can open-cell foam be sprayed on top of a radiant barrier, or is this even necessary?

I'm not sure if it will stick to the foil backing or not, but it will completely negate any benefit you would get from the radiant barrier. Radiant barrier needs an air gap otherwise it transfers the heat of what it is touching. You can grab a piece of foil sitting on a pan right out of the oven without burning yourself, but if you grab the pan with the foil on it you won't be so lucky.

I did a lot of research on insulation and we ended up with blown in fiberglass insulation in the walls and attic. Had rock wool been in the budget we would have gone that route, but were fighting covid price hikes and material availability at the time. Read some nightmare stories about spray foam off gassing and hidden rotting due to the spray foam, so we crossed that off the list.

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