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We are completing construction of a 1½ story house in Hanover, N.H.

user-6724719 | Posted in General Questions on

We are completing construction of a 1½ story house in Hanover NH. There is an unfinished “bonus” room over the 3 car garage. It has multiple windows. The plan is to someday convert this to a mother-in-law quarters. Currently, there is no ventilation, and no heating or cooling. Last winter icicles formed from the rafters, and one of the workers mentioned that there was some moisture (dripping from roof) on hot humid days this summer. We are concerned that the extreme temperatures will cause damage because of the water accumulation in the room. The room is now much like an unfinished attic, except there is absolutely no ventilation.

Questions: Should we add some insulation to the ceiling and / or walls to avoid the ice and dripping? If so, how much? Is there something else that we should do? Is this normal?

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  1. Expert Member
    Dana Dorsett | | #1

    A small amount of ventilation would keep the room cooler in winter with less solar gain to get the ice dams started (or were the icicles indoors?).

    The roof can be either vented or unvented when you install insulation, but a vented insulated roof would be less ice-dam prone.

    How deep are the rafters?

    Is soffit-to-ridge ventilation even a possibility for the roof deck?

    In the mean time, a low power 10cfm supply ventilation fan like the Panasonic FV-01WS2 (or the 20cfm FV-04WS2 ) running continuously should be enough ventilation purge moisture and avoid excessive water accumulation from the room.

  2. Jon_R | | #2

    I'd also stick a wireless humidity/temp sensor in the problem area so you can monitor conditions.

  3. GBA Editor
    Martin Holladay | | #3

    In addition to the advice already offered, here is my advice:

    1. You need to be sure that you don't have a roof leak.

    2. It sounds like the interior of your garage is unusually damp. This can occur if your builder didn't do a good job with exterior grading. It's essential that the grade be sloped away from the garage in all directions. It's also best if the exterior grade at the perimeter of your garage is well below the lowest wooden components of your walls. In some situations, roof gutters connected to a conductor pipe that conveys the water far from the building can make a big difference.

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