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Community and Q&A

Is insulated vinyl siding worth the cost and is it effective? I am on the coast of Maryland.

talusscree | Posted in Energy Efficiency and Durability on

Vinyl siding is inherently ventilated typically so it seems that any insulating value would be washed out. If that weren’t an issue, isn’t the relatively thin insulation enough to cause vapor drive issues in the winter? Minimum exterior foam thickness for my climate is 1″ but 1.5″ would be safer. We usually opt for 2″.

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  1. dvaut | | #1


    In one of my previous jobs we used to almost exclusively install vinyl siding with the EPS glued onto the backside of the panel. Usually it was a certainteed product and they do a very good job at manufacturing vinyl siding. That being said, I think there are better ways to insulate and air seal the exterior wall of a house. First of all there is no way to tape the seams of the insulation. Because the insulation is the area of the panel's exposure there are a lot of seams. Also the foam is not totally continuous since you need a gap at seams to allow for the siding expansion/contraction. The insulation does however help the panel lay flatter on the wall because it is more rigid than a regular panel. EPS is the only type of insulation I have ever seen on the back side of siding. You were concerned about vapor drive. EPS is more vapor permeable than other rigid insulation boards. I think you would be better off applying a rigid board that is not integrated with the siding panel. Two layers of 1" with staggered seams would work best. XPS and polyiso with a foil face will stop the vapor drive you are concerned about. Taped both these boards will also be a lot tighter and can also act as a weather resistant barrier if detailed right. R-Value per dollar, you would also be cheaper with the rigid boards as well.

  2. GBA Editor
    Martin Holladay | | #2

    The disadvantages listed by Dillon are real. But I think that Dillon overestimates the ability of insulated vinyl siding to dry to the exterior. Without the traditional air gap that ordinary vinyl siding provides, you end up with a type of siding with very little, if any, ability to dry to the exterior. You end up with all of vinyl siding's disadvantages (it's ugly) with none of its advantages (a built-in ventilation channel).

    The best way to improve the thermal performance of your wall (assuming that you are planning to install vinyl siding) is to install a continuous layer of rigid foam with taped seams, followed by ordinary (uninsulated) vinyl siding.

  3. dvaut | | #3

    I should have been more clear. My point that EPS being more vapor permeable was that Mike may want to use a less vapor permeable insulation, not that EPS would allow drying to the exterior. The less vapor permeable foam board would prevent a water vapor drive to the interior. I also totally agree that with insulated siding you loose a significant portion of your air gap. That is why I suggested regular siding with foam board instead.

  4. RD3Sunworks | | #4

    Not everyone thinks vinyl siding is ugly. My guess is that most people in the country do not think it's ugly.

  5. GBA Editor
    Martin Holladay | | #5

    Fair enough. I actually have a soft spot in my heart for vinyl siding, because it performs so well. Good performance is a kind of beauty.

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