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Condensation in tiny house

Komakulshan | Posted in General Questions on

Recently tore out my ceiling insulation due to this same issue – and then checked the walls – no good!  I’ve got some work to do!

I used tongue and groove pine planks on the interior of my tiny house without air sealing the walls or ceiling- yes a mistake.  The Tyvek against the exterior wall has a bit of condensation on it.  I’m looking for recommendations on air sealing behind the T&G pine.  I’ve seen info here on a product called Intello – is this the one?

Other mentions were about something called Membrain… how does this compare with Intello?

Remember – Can’t use sheet rock in a tiny house…  Locality is Western WA – cold and wet.

Thanks for the help,

Dave

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Replies

  1. Expert Member
    MALCOLM TAYLOR | | #1

    Dave,

    You can use a variety of materials as an air barrier. Probably the easiest so that the T&G pine goes back in the same plane are either 6 mil poly or a variable-perm membrane - the type isn't the important.

    How is the ceiling constructed? Is it vented? And out of curiosity: why can't you use drywall in a tiny house?

  2. vashonz | | #2

    I'm not sure if an air barrier will prevent condensation.
    More detail is likely needed to answer all the questions about the cause.
    -Condensation is caused by an object dropping below the dewpoint for a given psychrometric condition.
    -Air sealing to prevent warm-moist air from moving from interior into the wall/roof may help that.
    -If there's not enough insulation to keep the 'air barrier/drywall/not-drywall' warm, you may just move the condensing surface inward.
    -Small spaces are difficult- the size relative to number of people occupying that space can greatly cause a change in RH due to respiration.

  3. jbtvt | | #3

    "Membrain" sounds interesting, wonder the exact MOA for it. Possibly dessicant embedded in channels with tiny holes around pores, that would swell and distort the nylon, pulling pores open? Wonder what the life cycle is on something like that either way, most dessicants in window spacers turn to mushy chalk after a few years of water exposure.

    Regardless, I wouldn't use it for your application. I'm one guy in a 2000 sq ft house and my humidity is currently 40%. Your humidity is going to be above the 50-60% threshold for the Membrain "venting" almost all year long, in such a tiny space, and you'll just be right back where you are now with lost time and less money to boot.

    Best bet IMO would be to stick with traditional 6 mil poly. Do not use any oil coatings on your wood or it will def grow mold, and if you haven't already I would coat all sides and edges with acrylic poly, or a clear matte like Superdeck before replacing it to try to keep it drier. Or go with 3/8" drywall and tape your seams with Durabond, house will fall apart before that stuff cracks.

    Edit: and alternatively you could just insulate with foam and seal all gaps, two birds one stone.

  4. Jon_R | | #4

    +1 on measuring and controlling humidity.

  5. Komakulshan | | #5

    Thanks all for the replies:

    I think I will go with Intello since I hear it is more durable than Membrain and I'm blowing in wool insulation. Walls are 2x4's : R14 - should be warm enough to prevent interior condensation.

    https://foursevenfive.com/intello-plus/

    Sheet rock in a tiny house is in general too heavy and tends to crack when the house is transported. (Tiny house on wheels)

    Ceiling will be air barriered and vented: Im looking at SmartBaffle.

    https://dciproducts.com/smartbaffle/

    Thanks again for the excellent advice on this forum. I have to cancel out of my subscription as money is tight right now and I've got to save up to buy building materials!

    Dave

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