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What would cause water dripping from a cedar cathedral ceiling?

GBA Editor | Posted in General Questions on

No pipes are involved. There are 2 skylights, but the drips are also above the skylights . Only one side of the ceiling is involved. The room has a ventless gas fireplace. Would this cause the problem?

Replies

  1. User avatar GBA Editor
    Martin Holladay | | #1

    Thelma,
    The most likely cause is condensation of moisture contained in the indoor air.

    Less likely (but possible): you have a roof leak.

    Your unvented heater is, of course, releasing a lot of moisture into the interior of your home. Most energy experts advise that unvented space heaters should never be installed or used.

    Is there an air barrier installed behind the cedar boards on your ceiling?

  2. User avatar GBA Editor
    Martin Holladay | | #2

    [Second post from Thelma:]

    I asked this question earlier and received an answer. Thank you. More information: The room is 30 ft by 20 ft and is 15.5 feet high. The problem persist in the summer when the fireplace is not used. I'm not sure what you meam by air barrier. The cedar ceiling is nailed to the rafters. There is rolled insulation between the ceiling and the roof. There are outside vents on the 2 foot wide overhang to allow air there are also vents on the peak coming down. All around the room there ia a 2 foot boxing. The room was painted 3 coats with Benjamine Moore acrylic polyurethan. The problem seeded to start with the knots leaking. We also have pot lights in the ceiling. These are rarely used.
    Thelma

  3. User avatar GBA Editor
    Martin Holladay | | #3

    Thelma,
    Your cathedral ceiling sounds like a poster child ceiling — for what not to do. It incorporates all of the mistakes that lead to performance problems.

    1. The finish surface is boards.

    2. There is no air barrier.

    3. There are recessed can lights.

    4. The rafter bays are vented in such a way that air movement through the insulation is increased.

    5. The chosen insulation is air-permeable.

    6. Finally, there's an unvented gas fireplace in the room.

    An air barrier is any material that stops air flow from the interior of your home to the exterior. Examples include taped drywall or taped rigid foam insulation.

    To learn more about air barriers, visit these pages:
    https://www.greenbuildingadvisor.com/green-basics/enclosure-and-structural-overview

    https://www.greenbuildingadvisor.com/blogs/dept/building-science/how-air-affects-house-part-1

    https://www.greenbuildingadvisor.com/air-leaks-waste-energy-and-rot-houses

  4. Riversong | | #4

    Thelma,

    Where are you located? What's your climate?

    [website mavens: we simply have to have a required location field for questioners]

  5. User avatar GBA Editor
    Martin Holladay | | #5

    Thelma,
    On a different page, you asked the question, "What do you suggest we do?"

    You need to stop interior air from entering your rafter bays. That requires an air barrier. To address the problem, you should install taped drywall over your existing board ceiling. Remove all the recessed lights. Be sure to air-seal the electrical penetrations in the ceiling.

    If you're happy with your new drywall ceiling, just install surface-mounted lights (for example, track lighting) on the drywall.

    If you want a board ceiling, install new cedar boards on top of the drywall, and then put up the track lights.

    Of course, if you are going to all this trouble and expense, it would be a good idea to install rigid, air-sealed ventilation chutes between the insulation and the roof sheathing. It would also be a good idea to upgrade your insulation from fiberglass batts to dense-packed cellulose or spray foam.

  6. Jeff | | #6

    Is it possible that the ventless fireplace is heating the cedar to cause the leaks?

  7. User avatar GBA Editor
    Martin Holladay | | #7

    Jeff,
    No. However, it is possible that the moisture that the ventless fireplace adds to the air is contributing to the ceiling condensation problem.

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