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Log cabin with housewrap (air barrier)?

timmywo | Posted in Green Building Techniques on

Hello,
I am based in South Poland where we have Summers +30c and Winters -30c, I am in the process of building a log cabin from reclaimed beams.

My wall design will be as follows…
1. External logs (20cm thick) with chinking and Mineral Wool in joints to seal gaps
2. House Wrap
3. Mineral Wool 20cm
4. Vapour Barrier
5. Final wall finish

My concern is with layer 2, the House Wrap. I wish to make the property as air-tight as possible but worried moisture may get stuck between the External Logs and House Wrap, resulting in the logs rotting.

Maybe I should reverse the House Wrap to allow moisture from layer 2 to 3 and let the Mineral Wool deal with it? (just an idea, maybe crazy). Or do away with the House Wrap and allow the logs to breathe in both directions, but worried I then lose the opportunity to have airtight insulation.

Keen to hear others thoughts regarding this, there is very little regarding this on the web for Log Cabins.

Many thanks

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Timmy,
    Almost all brands of housewrap are vapor-permeable. That means that housewrap will not trap moisture.

  2. timmywo | | #2

    Thanks Martin,

    Yes, I am aware of that, but for some reason until now I thought it was only in one direction. Now I think about it they are water resistant and vapor permeability.

    If the logs are well sealed and maintained there should be very little water hitting the House Wrap and therefore getting trapped, any vapour can pass freely.

    I am assuming the water resistants works best in one direction, hence the front face of the House Wrap, but vapor permeability works in both directions?

    I think that makes sense and follows all I have read.

  3. GBA Editor
    Martin Holladay | | #3

    Timmy,
    There is no difference between the two sides of housewrap. It doesn't matter which side faces out.

    The vapor permeance and the water resistance and the air resistance of the housewrap are all the same in both directions.

  4. timmywo | | #4

    Great, thanks Martin, that clears that up then!

  5. Expert Member
    Malcolm Taylor | | #5

    Timmy,

    To reinforce what Martin said, this is from Dupont's site:

    "Tyvek® HomeWrap®, Tyvek® StuccoWrap®, Tyvek® DrainWrap™ and Tyvek® CommercialWrap® are equally effective in both directions and the logo may be on the inside or outside. However, Tyvek® StuccoWrap® and Tyvek® DrainWrap™ have a specially engineered surface that should be placed with the grooves facing outwards in a vertical direction. "

  6. timmywo | | #6

    Thank you Malcolm, all the info I have read fits into place nicely now. The danger of assumptions, especially ones you do not even realize you are making.

    Thanks again to both of you, on to the next challenge! Wish you both an early Happy New Year

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