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-   -   Insulating a Cathedral ceiling in California (http://www.diychatroom.com/f19/insulating-cathedral-ceiling-california-64463/)

wolfsden 02-15-2010 04:26 AM

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.:(

Scuba_Dave 02-15-2010 08:24 AM

What exists for ventilation right now ?

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

Gary in WA 02-15-2010 05:43 PM

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

wolfsden 02-15-2010 06:27 PM

Ceiling Insulation
 
3 Attachment(s)
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. :thumbsup:

Gary in WA 02-15-2010 08:56 PM

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

jlhaslip 02-15-2010 09:12 PM

Quote:

Originally Posted by GBR in WA (Post 400555)
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.

wolfsden 02-15-2010 10:04 PM

Insulation
 
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.

Scuba_Dave 02-15-2010 10:17 PM

Rafter vents in each bay for ventilation

http://www.metrosupplycollc.com/image/33537535.jpg

The joists running across the room just above the walls need to stay
They keep the walls from spreading out

wolfsden 02-15-2010 11:52 PM

vents
 
do the rafter vents run the full length of the ceiling or are they partial like in the picture?

jlhaslip 02-16-2010 12:46 AM

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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