How to insulate a cathedral ceiling?
I am planning a deep energy retrofit of my home. I am located in Calgary Alberta. Climate zone 3a. Average winter temperature in Dec and Jan is -14c (7 deg Fahrenheit). But it can get down to minus -50f, and -20f is not unusual for extend periods of time during the winter.
My living room has a cathedral ceiling over it. The existing roof/ceiling construction is: paint, GWB, poly V.B., 2x10 joists, 8”batt insulation, 1” roof decking, 1/4” ply, SBS roof membranes. The roof is presently vented with eve vents down low and the roof dumps into a vented attic on one side of the house. I will be adding a second floor where the attic is presently located so the top venting will be interrupted.
I do not want to loose any height in the living room so my intention is to remove the membrane and add insulation above the roof sheathing. I would prefer not to use foam for environmental reasons(persistent chemicals). I plan to add minimum 6” of Roxul (R-24) over the sheathing.
I have several concerns with this approach:
One, this roof assembly becomes a semi (half) vented roof assembly. I am concerned that I maybe paying a significant energy penalty by maintaining the venting in the joist space? If cold air is flushing this space what good is the insulation above?
If I seal the joist space I may have condensation problems.
Has anyone had experience with this type of retrofit condition? Any suggestions would be greatly appreciated.
Posted Fri, 01/03/2014 - 17:40
Edited Fri, 01/03/2014 - 17:51
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