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Vapor barrier or no vapor barrier?

Richard Deschenes | Posted in General Questions on

I cannot seem to find a definitive answer to my question. I own a family campground in western NY which is open from May 1st through mid October. The main building is an A Frame with wings on both sides of the “A”. There is no insulation and the inside of one of the wings is unfinished, the ceiling is roof sheathing and rafters. The building is closed during the cold winter months while I sun myself in Florida so heating is not needed. I do want to add air conditioning to make the space more usable during the hot, humid summer months. I am so confused about the info I read on how to insulate. Vapor barrier or no vapor barrier, ventilation or no ventilation? The building is used occasionally on weekends and will not be cooled constantly but only when needed. Since the roof line ends at the A frame portion of the building, there is no ridge and no way that I know of to add ventilation other than at the soffit.

Any help will be appreciated.

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Replies

  1. User avatar GBA Editor
    Martin Holladay | | #1

    Richard,
    Stop worrying about vapor barriers. If your building in New York state will not be heated, but will be air conditioned occasionally, you definitely do not want any interior vapor barrier.

    In your climate zone, building zones require insulation. That said, on an older existing building like yours, insulation is probably optional. If you install insulation, the cost of running your air conditioner will be much lower than if you don't install insulation. You would also save energy costs if you performed air sealing work (to limit leaks in your walls and roof). But the work is optional.

    If you don't care about high energy bills, all you have to do is install a big air conditioner and plug it in.

    If you want to keep your energy bills as low as possible, seal the air leaks and install insulation.

    Do you know how to do insulation work? If not, you may want to read a few articles. Here is a link to one such article: How to Build an Insulated Cathedral Ceiling.

    If you have a sloped roof assembly that you want to insulate, and if it's impossible to vent the roof assembly, you need to choose one of two approaches for creating an unvented roof assembly. The two choices are:
    Install closed-cell spray foam on the underside of the roof sheathing
    Install rigid foam above the roof sheathing. (If you choose this option, you will in most cases need to install a second layer of roof sheathing above the rigid foam, along with new roofing.)

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