Tearing off my roof – reducing heat gain in my finished attic w/cathedral ceiling?
Greetings all – Thanks for maintaining such a fantastic forum. I’ve spent the past few hours reading and learning, and I’m seeking advice on my particular unique situation.
The background – I have a 1944 Cape Cod-style house located in Portland, OR, zone 4C. The attic is a finished space with a cathedral ceiling which we use as our bedroom. The rafters are 2×4 with the cavities currently insulated with what is probably R11 fiberglass and no ventilation. The interior is finished with drywall which continues all the way to the peak of the roof – there’s no “flat space” at the peak other than a ~6″ board.
The knee walls are also insulated with r11-13. There is also a small area beyond the kneewalls (under the lowest part of the roof) that has conventional insulation of fiberglass batts between joists.
It’s time to replace the roof – 2-3 layers of asphalt on cedar, all on top of the old-style 1x planks. It seems that the “right” way to do this is to tear off everything down to the rafters, which gives me the opportunity to try to add insulation and/or ventilation from the outside.
First let me state that in our relatively mild climate, reducing our winter heating bills isn’t our biggest concern – they are already pretty low with our ancient oil furnace, and should be lower after our gas conversion. What I’m most interested in is reducing the summer temps in the attic bedroom, presumably by reducing the heat transfer from the sun-heated roof.
One added complication is that the roof has essentially no overhang, which makes eave vents difficult.
The question is – what to do? Given the extremely limited depth of the rafter bays, I could get a few more R’s using spray foam or rigid foam, but I’m not sure that it would be worth the added expense. One roofer has suggested adding pre-fab channels, edge vents and a ridge vent in order to ventilate the roof ,but this just cuts the space available for insulation even more.
Another thought I had was using Energy Star shingles to reduce heat gain but again I’m not sure they would be worth the expense.
So – what would you advise in this situation? Apologies in advance for my any unclear rambling.
Thanks for your advice.