open cell v. closed cell (rainy climate)
My brother, who lives in the northwest coastal area (Portland, Oregon), has a question that I agreed to ask on Breaktime.
He has cathedral ceilings in his upstairs, second floor. Previously, the ceilings were open, with the rafters exposed.
He has lowered his ceilings with new, 1 x 6 boards and is ready to have insulation installed – after which he will sheetrock the open area.
His question regards open cell v. closed closed insulation. The R factor difference between them is not a concern to him. He needs to know about the vapor factor through open cell insulation – and the future prospect for condensation and mold.
Should he have open or closed cell insulation blown into the still exposed ceiling spaces? His deadline to decide is July 28. He will be much obliged.
Replies
Hep me hep my brother. Anybody. Please.
Never heard of open/closed cell as far as blown-in insulation is concerned. More details?The Woodshed Tavern Backroom
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kenhill3,
I'm pretty sure my brother is asking about spray foam insulation.
The climate is on the exterior so that means little.
How he controls the interior climate might mean something.
I have never yet seen a good reason for using open celled instead of closed though.
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Thanks Piffin. Your response and all that I've read since posting convinces me that his far and away best choice is closed cell.
He and his wife heat their house about six months of the year with a forced air, gas furnace and leave the doors and windows open the other six. Their average, year round humidity level is pretty high, even though the temperature is rarely high enough to be uncomfortable.
I just did this in Newport. Oregon Residential Specialty Code R806.4 calls for R-20 of air impermeable insulation in direct contact with sheathing. Closed cell is what you want. I used 3.5 inches of closed cell and R-38 fg batts.
Also....R806.4.3 says...Where wood shingles or shakes are used,a minimum of 1/4 inch (6mm) vented air space seperates the shingles or shakes and the roof underlayment above the structural sheathing.
You can also check out Buildingsciencecorporation.com. Unvented attic assemblies.
Thanks atrident. I'm passing on to my brother that link and those citations.