Floor Insulation Vapor Barrier

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This topic contains 1 reply, has 2 voices, and was last updated by  nelubian 3 years, 3 months ago.

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    I am using a Tumbleweed Low Wider Trailer so the bottom of the trailer came sealed with steel. We just finished laying our rigid insulation for the flooring, sealing edges with spray foam, and lining the steel edges with mounting tape and we’re wondering if or what you recommend to use as a vapor barrier before laying the floor plywood? Is a simple sheet of plastic something you’d recommend? Or is this not necessary with because the trailer came welded with steel on the bottom.

    In talking to an engineer the only concern with the vapor barrier is the potential condensation on the bottom side of the plastic, that would potentially dampen the insulation? With the heated environment above and the cold steel trailer below do you think this will be a concern?



    Hi, I am not an expert, but: if it is a polystyrene insulation, then it is a vapor barrier by itself. A vapor barrier is usually set between interior liner and insulation, in regions where the temperature drops below 0 degree celsius. Because vapor coming from the interior becomes ice somewhere in the insulation (breathing insulation, certainly). Some insulation like polystyrene or polyurethane (closed cell) are vapor barriers by its nature, automatically making house a thermos.

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