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Will this suspended floor assembly risk condensation?

StephenN | Posted in General Questions on

Working on a renovation project where I am completely rebuilding the floor but am not confident about the best floor assembly. Would be grateful for any advice.

Floor assembly (top to bottom):

A. 30mm cedar flooring.
B. 80mm joists.
    C. Between top: 30mm radiant flooring bags (foil lined bags of gel that are laid over PEX pipes to conduct heat from pipes to flooring above; the bags are laid over the pipes but they do not form an air seal)
    D. Between bottom: 50mm rockwool insulation.
E. Smart membrane for air barrier.
F. 120mm beams.
    G. Between: 120mm rockwool insulation.
    H. Under: 50mm rockwool insulation.
I. House wrap.
J. Hardware cloth.

Foundation type: open piers about a meter off the ground. There is no skirt or wall so the air under the house should be the same as the outside air. The soil is very wet under and around the house (high water table). I will be putting down a plastic sheet over the soil under the house to cut down on some moisture.

Climate: The house is near a lake so humidity is always high, but there is a lot of wind as well. Only two or three months out of the year need cooling. Winters are cold with lots of snow. Closest to US zone 5 (but not located in the US).

Questions:

1. What is the best material to put in location “I” (where I planned to put house wrap)? I want to prevent wind washing, allow trapped moisture to dry, but I’m worried that the vapor-open house wrap will allow moist air to condense in the floor assembly.
2. Is the smart membrane (“E”) in the middle of the assembly going to be problematic? That is the best place for getting a good air seal, but I don’t know if it will introduce condensation problems.

Attached is a diagram of the assembly.

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Replies

  1. GBA Editor
    MALCOLM TAYLOR | | #1

    Stephen,

    Your proposed assembly will work fine. Especially if you limit the amount of moisture that can rise from the soil underneath with the poly, there is no reason to think moisture will accumulate in the floor system, or that if some incidental amount does get in it won't dry.

    1. StephenN | | #2

      Malcolm, thank you very much for the advice. And apologies for this late response. For some reason I could not reply to your comment until today (I got an email notification, but your response wouldn't show up when opening the page).

      I will proceed according to plan then. Thanks!

      1. GBA Editor
        MALCOLM TAYLOR | | #3

        Stephen,

        The problem was on my end. None of my posts were appearing. Seems to be fixed now.
        Good luck with your reno!

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