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Community and Q&A

Best way to insulate solar tube skylights?

user-980774 | Posted in Green Building Techniques on

We are remodeling an old DARK house with limited opportunity to add windows.
Plan was for 2 solar tubes in bathroom. Owners were so happy with additional light
we are adding more. What is best way to insulate tubes. The bottom 14″ will be in the new cellulose attic insulation, but 2′-4′ will be exposed above insulation.
Fiberglass batts and duct tape would work but be tough to do neatly with no gaps.
Any suggestions?

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  1. Expert Member
    ARMANDO COBO | | #1

    We've use 2" spayed CC foam in the past, but truly, when calculating EE and energy loses, we’ve found they are small, unless you add a ton of them, I supposed.

  2. user-980774 | | #2


    Can closed cell foam be left exposed in an attic?

  3. GBA Editor
    Martin Holladay | | #3

    To enclose and protect any insulation on the exterior of a skylight tube, you could build a box out of rigid foam. (Seal the corners of the box with housewrap tape.)

    Or, for a slicker and more tubular solution, you could buy a large diameter Sonotube, cut it in half lengthways, and assemble the Sonotube around the insulated skylight tube. Then tape the two halves of the cardboard Sonotube back together.

  4. Ken Levenson | | #4

    Sorry to promote but this might be of interest: Lightway Solar Tubes provide a thermal break where you need it at the insulation layer. Find out more here:

  5. user-659915 | | #5

    Best way to prevent unwanted heat transfer through tubular roof lights is not to install them. Even with the sides insulated you still have an R5 hole top to bottom through your R50 ceiling. Use high-efficiency LED lighting instead and you'll save energy- and money - overall.

  6. user-980774 | | #6

    Well James thanks for the advice. I guess the same arguement can be made for windows.
    Think how much energy and money would be saved not having all those R4 holes in my R40 wall!

    I was not a fan of the solar tubes when they first came out, but after seeing the difference NATURAL DAYLIGHT can have on dark, interior rooms, I now recommend them often in remodel projects.
    Also dark interior rooms need light 12 months of the year and I live in an area with a 3-4 month heating season, so do the math of lights on for 12 months or VERY minor heat penalty for 3 months.

  7. dankolbert | | #7

    Why do you think you need to protect the exposed foam? Is there storage space around it?

    And I'm with you - I haven't used them very often but I think they're a nice solution when there aren't any others.

  8. user-980774 | | #8


    Was not sure if closed cell foam could be exposed in attic, no storage issues.
    If it can be left exposed, it sounds like the best option.


  9. sgeco | | #9

    You can ask the solar tube skylights manufacturer by yourself or goole their installation instruction, there's no insulation needed. If you are worrying about the condensation that may occur inside the tube, most unit have condensation release system that keeps moisture outside and is water tight. Heat will not lose through convection because the tube is sealed and there are no air current. However, manufacturer's recommendation will still prevail so better ask them, each product is differently made and with different specs.

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