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I have a two-story house. Half the house has a cathedral ceiling (which will be left as is) and the other half has a traditional attic with no soffits. The only ventilation in the attic comes from two gable vents at each end of the house.

How should I insulate this type of attic? I am contemplating adding insulation to the bottom of the roof deck and adding more insulation to flooring in attic; I think this is called a sealed attic. Is this appropriate for my climate?

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1 Answer 1

If I were building the house in southern California then I wouldn't do this, especially if you were using asphalt shingles.

An unventilated attic in a warm climate like this can get extremely hot and will greatly decrease the life expectancy of asphalt shingles. Over time they will start to curl prematurely from the heat. If I were to do this I would insist the following courses of action:

  • Heavily insulate without sealing gables

  • Have at least a 1 foot overhang with ventilated soffits

  • If 1 foot overhang is not possible, then install an attic fan to assist in proper ventilation of the attic

  • If neither of these are possible then forgo asphalt shingles for something more appropriate for extreme heat like terracotta or slate shingles.

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Not having adequate ventilation tends to void shingle warranties. That was the first thing mentioned when I did my re-roof. –  Fiasco Labs Aug 21 '12 at 17:27

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