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Community and Q&A

Reflective insulation barriers in a floor system built on piers

rockies63 | Posted in Energy Efficiency and Durability on

I saw a question in a cabin building forum I visit about reflective barrier insulation for crawlspaces and floors built on piers. The member was wondering if this would be a viable way of increasing his floors insulation (he can’t access the floor from the underside – it’s on low piers).

Any ideas or opinions?

Crawl Space R-21

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  1. Expert Member


    For reflective barriers to be at all effective they need an airspace on one side. In a floor, with limited depth, the space is better used by installing more insulation.

  2. rockies63 | | #2

    Malcolm, thanks for your reply. This method seems to be suggesting that by using two layers of the product an air space is created between them which acts as the insulation (I don't see any mention of adding batt insulation anywhere in the floor system).

    I find it odd that in their FAQ section they say they require that the product be stapled in place and yet they claim that the product will also act as a vapor barrier if the seams are taped (not the edges?). Wouldn't installing this product trap moisture in the floor system as well?

  3. Expert Member
    BILL WICHERS | | #3

    Insulation works to reduce heat transfer by preventing the movement of air, and that movement isn’t just bulk movement but also small circulating currents. Better insulation better limits this air movement and the associated transfer of thermal energy. Reflective insulation helps, but only in some cases. A thick air gap between two radiant barriers will not limit the circulation of air as well as a dense mat of something like fiberglass, or the tiny air pockets in the foam of something like Polyiso.

    If the material you’re considering is what I think it is, it probably will work as a vapor barrier just fine if properly sealed since it’s basically a plastic film. You are correct that it will need to be sealed at the edges too and not just at the seams to act as an air barrier.


  4. Expert Member


    here are two GBA Spotlights that deal with similar situations:

    Going back to the illustrations on the site you linked to. If the whole floor cavities are devoted to the two reflective barriers, what R value do you end up with as compared to filling them with insulation? I guess another way of putting it would be: If you could just staple-up reflective barriers in any wall or ceiling assembly and get adequate R values, why do we all use insulation?

    Edit: The reflective barrier would work as a vapour barrier. Unlike air-barriers, vapour barriers don't benefit from sealing.

  5. GBA Editor
    Martin Holladay | | #5

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