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Community and Q&A

Skylight insulation upgrade

Michael__R | Posted in General Questions on


My name is Michael and I live in a bungalow in the 7A climate area.

I am looking to upgrade the insulation around my skylights and bringing it up to code in my area.

The wall assembly is 2” by 6”.  The existing insulation is not properly installed and I plan on replacing it.

Should I replace it with insulation and form board?  The ceiling is sloped which adds to the difficulty working in the attic.

Do I place insulation/form board to the top of the roof sheathing or do I leave a gap?

I look forward to your suggestions about products and installation.

Thanks in advance.


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  1. GBA Editor
    Martin Holladay | | #1

    When it comes to your 2x6 walls, it is certainly possible to add rigid foam to your walls if you want to. If you install the rigid foam on the exterior side of your walls, you'll need to either (a) temporarily remove the siding and re-attach it later, or (b) install new siding. For more information, see "How to Install Rigid Foam Sheathing."

    If you want instead to install rigid foam on the interior side of the wall, see this article: "Walls With Interior Rigid Foam."

    When it comes to improving the insulation in your sloped ceiling, this article will explain all of the options: "How to Build an Insulated Cathedral Ceiling."

  2. NormanWB | | #2

    During the construction of my new house, I insulated the skylight chases with two layers of 2' poly iso (R-24 total), sealed any edges with spray foam, and wrapped it in some radiant barrier material.

  3. GBA Editor
    Martin Holladay | | #3

    If you are talking about the skylight shaft (or well), see this article: "Insulated skylight shaft."

  4. Expert Member
    Dana Dorsett | | #4

    The biggest heat leak with skylights are the skylights themselves- the insulation around them is sort of "in the noise".

    If you don't need a sharp, clear view of the sky and want shadow-free daylighting, Wasco sells ~U0.22-ish (R4.5 instead of the typical R2) aerogel-insulated skylights. They're not cheap, and they're not what you're used to,- a bit of smoky/foggy neutral density filter effect, but they're also not bad.

    In a zone 7A climate, depending on the orientation and local weather you may get more beneficial solar gain heating out of a typical U0.5-ish skylight than it loses, but I suspect going with an aerogel skylight would still use less energy, despite somewhat lower solar gain, since it's less than half the heat loss.

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