Is a sealed attic appropriate for Southern California?

Question

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?

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.