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Question DetailsAsked on 5/25/2018

What to do with roof with no air flow/space? Condensation forms on vaulted ceiling under it.

It is a low slope shingles roof over cathedral ceiling house with no attic. I have added sheet insulation to keep the heat in but as a result now there is no space between it and the sheathing under the shingles. I heard that adding ridge vent or soffit vent won’t do any good if there is no space for air to move through. Is there any solution besides replacing the whole roof? Thanks.

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1 Answer


Insulation can sometimes solve this issue, attic ventilation generally will only help if the moisture is coming from above (though to prevent attic mold and rot it should be ventilated - not fully blocked with insulation as yours sounds like). In many cases putting in directed airflow at the peak area of the cathedral/vaulted ceiling is necessary to remove the moist warm air accumulating there. In some cases you lose the energy conservation battle (especially with single-layer T&G ceilings or zero-attic construction in cold winter area) and in addition to what insulation you can put above it (while still leaving 2-3 inch ir ventilation between soffits/eaves and ridge vent) you have to use directed airflow or a large ceiling fan to move heated air at the peak area to heat it up above the dewpoint (where condensation starts forming) and to circulate enough air to keepthe surface dry. Sometimes this is limited to one localized spot (commonly areas with less snow cover or sun exposure in the winter), sometimes at all high ceilings in a house.


Answered 2 years ago by LCD

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