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I have a problem with humidity management during winter in my off-grid secondary home

levassep | Posted in General Questions on

When we get there the air inside can be as low as -20C so when we go back all the humidity we produced is collecting-condesing on the vapor barrier (Isofoil).

The building is 3 years old and was built quite tight by myself. 2 floors, 28×32, heat source wood stove only.

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  1. GBA Editor
    Martin Holladay | | #1

    I looked up Isofoil, and discovered that it is foil-faced EPS (expanded polystyrene).

    You told us that you have noticed that moisture is condensing on the Isofoil. I'm guess that means that your house is under construction -- it hasn't been completed yet -- and that you have foil-faced EPS on the interior, without any drywall or wall finish over the foil-faced EPS. Is that correct?

  2. GBA Editor
    Martin Holladay | | #2

    I'm going to paint the scene. It is mid-winter in Quebec. You have a weekend cabin in the woods. You arrive on a cold day, and you notice that the indoor temperature is -20°C (-4.0°F). You light a fire in the stove, and it takes about 12 hours or 18 hours to warm up the cabin (because everything indoors is so cold -- there is thermal mass in your house).

    You put a pot of water on the stove to make tea or wash the dishes. You clear the snow off your boots and you brush the snow off your coat. The melting snow evaporates, and the kettle on the stove begins to boil. Pretty soon, you notice condensation on the foil-faced EPS installed on your walls -- and on your windows, too.

    Have I painted the picture correctly?

    Here's my analysis:

    1. Nothing is wrong. This is normal.

    2. You solve the problem by putting another log in the wood stove and being patient. Eventually your cabin will warm up and the condensation will evaporate.

  3. levassep | | #3


    The house in not under construction, it is finished. The interior walls are clad with vapor barrier and painted gypsum board. The cathedral ceiling is clad with Isofoil and 3/4'' pine tongue and groove plank. Wall cavity is 6'' fiberglass and wall exterior is 2'' styrofoam with taped air barrier

    I know that if a heat up the place the codensation will go bur not away the water is still in the air so when I go back and temperature goes down every surface that reach the dew point collects water on it and then it frozen there.

    So the second time I go there and heat up the place the ice formed on the Isofoil melt and water is dripping from the cathedral ceilling.

    My understanding is if I dont want it to occur I need the humidity to go away before reaching dew point, so I need to circulate the humid air outside.

    The solution I'm looking is with no duct work, is there any trough the wall solution to ventilate?

    I have found Lunos e2 but it is quite pricey . If I opt for this should I install juts one unit or two (one on each floor).

    Thank you I greatly appreciate your advices.

    Pierre L.

  4. levassep | | #4

    I forgot to mention that the ventilated roof is insulated with 18'' fiberglass.

  5. user-2310254 | | #5


    You said the house is off grid. Do you have a generator and/or battery bank?

  6. levassep | | #6

    Solar and battery bank. Also have a generator if needed but don't like to use it.unless really necessary.

  7. GBA Editor
    Martin Holladay | | #7

    I think that the phenomenon you are describing is unavoidable for a house that isn't kept heated all winter long.

    It sounds like your house has more moisture than usual. One way to address this is to open a couple of windows a crack while you are there, and while the wood stove is operating. Sure, you'll cool the house a little, and you'll have to burn a little more wood -- but the fresh air will help lower the indoor humidity a bit.

    Otherwise, relax. The frost is harmless. When you fire up the wood stove, the frost will go away.

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