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Community and Q&A

Roof vent baffle – foam worth it over cardboard? vb?

hyasinthgurl | Posted in General Questions on

Do plastic baffles cause moisture accumulation issues?
I could think they would trap moisture on the wrong side.

People seem to like to either buy the plastic baffles or construct rigid foam baffles but are cardboard baffles better.

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  1. GBA Editor
    Martin Holladay | | #1

    In my experience, the biggest error people make is to install a ventilation baffle in such a way that the baffle isn't airtight. That reduces the effectiveness of the insulation, and allows escaped moisture to collect near the ridge vent.

    Whatever product you use, make sure that the panels are installed in an airtight manner.

  2. hyasinthgurl | | #2

    Thanks Martin.
    I'll be trying my best to make it airtight.

    Any concerns about trapping moisture in?
    Obviously I'm trying to keep moisture out, but ....

  3. GBA Editor
    Martin Holladay | | #3

    If you pay attention to airtightness -- by installing a good air barrier above the insulation as well as below the insulation -- I wouldn't worry about trapping moisture.

    I'm assuming that you have the basics covered: that your ventilation channel is sized properly, that you have good soffit vents and good ridge vents (and a clear channel between them), and that the R-value of your insulation either meets or exceeds minimum code requirements.

    More information here: How to Build an Insulated Cathedral Ceiling.

  4. hyasinthgurl | | #4

    Well, I wish your assumptions were true.
    Is it a problem if the airsealing is not great below the insulation?

    Some of those ideals are not happening in this retrofit. Even if I could squeeze into some of the attic areas (which I can't ) I would not be confident of air sealing well below the insulation (other than the room we are working in). The insulation that is there is almost to code, in most spots. I'm working on correcting the insulation in the current room and the spots I can get to, also plan on installing a ridge vent and upgrading the soffit vents (next spring?).

  5. GBA Editor
    Martin Holladay | | #5

    If your ceiling assembly is leaky, all bets are off. You can definitely have problems with moisture accumulation and rot if you are unable to control air flow through your ceiling.

    However, if you have problems, it won't be because you chose the wrong material for your ventilation baffles. It will be because you were unable to control the air flow through your ceiling.

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