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Cape Cod Home – condensation on LL floors – mid-May through mid-September

Howard Kelley | Posted in GBA Pro Help on

Cape Cod Home – condensation on LL floors – mid may thru mid september… the basement is walk out with windows, slider, so a fair amount of air goes through.

I do understand the floor is colder than the air flow temp. The key piece of info is that there is no insulation under the concrete floor.

The real question…. can a layer of foam be put down over the concrete and then a sleeper floor over that ?? or simply the sleeper floor ? what is the correct way to mitigate that condensation problem on some level.

Also do not want to trap moisture and cause mold … (ie plastic … or foam that is not thick enough).

We have 2.5 inches of working space until slider would need to be raised.

Old timers… say build a dead floor. (sleeper floor). leave a space for air flow at the edges for the condensation and water vapor to dissipate … ” their words ..”you will likely never stop as long as doors and windows will most likely be open”.

Slider is open 80% of the time… as people use that entrance and exit …

Thx. Howard

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  1. GBA Editor
    Martin Holladay | | #1

    I don't know what an "LL floor" is. But you are evidently talking about an uninsulated concrete floor.

    If you have 2.5 inches to work with, the standard solution would be to install 1.5 or 2 inches of rigid foam (either XPS or dense EPS) followed by 3/4 inch plywood. The plywood is screwed to the concrete through the foam with TapCon fasteners. If you do this, you'll solve the condensation problem.

    Of course, if you want more room for thick flooring like ceramic tile, you may have to install thinner rigid foam.

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