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Old 02-15-2010, 04:26 AM   #1
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Insulating a Cathedral ceiling in California


I'm remodeling my family room and have torn out the dropped ceiling and would like to leave the cathedral ceiling and finish it with wood planks. I wanted to use denim insulation. I'm not sure if I just apply the insulation directly between the trusses or do I need to be concerned with ventilation. The sofit vents are still exposed and I was going to just cover them and insulate. I'm in Southern California. Any advice would be appreciated.

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Old 02-15-2010, 08:24 AM   #2
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Insulating a Cathedral ceiling in California


What exists for ventilation right now ?

Do you have a picture of the area?
No ceiling joists or rafter ties right now ?

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Old 02-15-2010, 05:43 PM   #3
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Insulating a Cathedral ceiling in California


As long as you leave or add something to keep the exterior walls from blowing out. Leave the ceiling joists or rafter ties (every 4' o.c.)., or add a structural ridge to carry the roof load. If a low pitch, the rafters need to be designed as beams. http://books.google.com/books?id=E5S...raming&f=false

For a Southern CA zip code (921), you need R-19 in the ceiling, or 5-1/2" of denim (3.5 R) insulation, plus an air space (1" or 2" depends on slope) above for ventilation. Otherwise you create problems, the least is the roofing manufacturer won't honor any claims on your material. The soffit vents are there for a very good reason. They let air in to exhaust out the ridge.

Be safe, Gary
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Old 02-15-2010, 06:27 PM   #4
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Insulating a Cathedral ceiling in California


Here are a couple of pictures of what I'm working with. Sorry if I get the termonology wrong but I'm new at this. The only ventalation currently are the sofit vents which now are open into the room. There are the beems that span the room to keep the walls from blowing out.
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Insulating a Cathedral ceiling in California-p1010832.jpg   Insulating a Cathedral ceiling in California-p1010831.jpg   Insulating a Cathedral ceiling in California-p1010830.jpg  
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Old 02-15-2010, 08:56 PM   #5
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Insulating a Cathedral ceiling in California


The rafters are far under-sized to be cathedral ceiling. It would involve a complete re-do. The bays between each rafter should be vented. The rafter ties and supporting 1x's should stay for structural integrity.

Be safe, Gary
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Clean the dryer screen in HOT water if using fabric softener sheets.
They leave a residue that impedes air-flow, costing you money.
Clean the ducting in the last six months? 17,000 dryer fires annually!
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Old 02-15-2010, 09:12 PM   #6
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Insulating a Cathedral ceiling in California


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Originally Posted by GBR in WA View Post
The rafters are far under-sized to be cathedral ceiling. It would involve a complete re-do. The bays between each rafter should be vented. The rafter ties and supporting 1x's should stay for structural integrity.

Be safe, Gary
Absolutely correct. The 2x6 rafters, less air space of 1 1/2", would allow only R12 insulation unless you did a foam ceiling.
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Old 02-15-2010, 10:04 PM   #7
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Insulating a Cathedral ceiling in California


Would spray foam be a better option and would I still need to vent? If I did use the denim how do I vent under the insulation? Is a certain product that I would install? I was looking into Armstrongs Woodhaven line for finishing the ceiling, I could always add furring stips...anyway this is the look I'm going for kinda like a plank ceiling.
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Old 02-15-2010, 10:17 PM   #8
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Insulating a Cathedral ceiling in California


Rafter vents in each bay for ventilation



The joists running across the room just above the walls need to stay
They keep the walls from spreading out
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Old 02-15-2010, 11:52 PM   #9
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Insulating a Cathedral ceiling in California


do the rafter vents run the full length of the ceiling or are they partial like in the picture?
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Old 02-16-2010, 12:46 AM   #10
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Insulating a Cathedral ceiling in California


full length in a cathedral ceiling is best. It allows ventilation all the way to the top. and you need vents up at the peak.

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