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-   -   cathedral ceiling insulation question (http://www.diychatroom.com/f19/cathedral-ceiling-insulation-question-73428/)

phelix17 06-11-2010 12:45 PM

cathedral ceiling insulation question
 
I bought a house in Tampa Florida which has cathedral ceilings in 50% of the house. It seemed really hot in these rooms, so I checked to see how much insulation was above. The answer? Zero. Apparently, when the previous owners replaced the roof, they glued and nailed plywood to the tongue and groove cedar above the beams, then put asphalt shingles on top. No insulation at all. They pocketed the insurance money and then walked from their mortgage. I bought it short, so I have no one to go after. I was wondering what the best way would be to insulate. The beams are 4 by 8, four foot on center. If there was an insulation remedy under the ceiling that would not be too thick, we might be able to at least save some of the beamed look, as this is a mid century modern home. I'm wondering about condensation issues if I try it this way. I think removing the shingles and building a proper roof would be too expensive. Any ideas? How do I R Value for the least bucks? Many thanks in advance. Tim

Ron6519 06-11-2010 01:14 PM

Unless there was insulation above the cedar, it probably never had any to begin with. Unless you cover the cedar from below and bury most of the beam, there aren't too many insulation options.
You could use foamboard and cover it with sheetrock or reboard it. You just need to be careful that the screws don't poke through the roof.
Ron

phelix17 06-11-2010 02:35 PM

Quote:

Originally Posted by Ron6519 (Post 454643)
Unless there was insulation above the cedar, it probably never had any to begin with. Unless you cover the cedar from below and bury most of the beam, there aren't too many insulation options.
You could use foamboard and cover it with sheetrock or reboard it. You just need to be careful that the screws don't poke through the roof.
Ron

Thanks, Ron, Can I put the foam board right against the cedar without having to ventilate? It doesn't seem like there would be any air there for moisture to form in any event.

Ron6519 06-11-2010 03:24 PM

How you insulate it would depend on the regional building codes.
Ron

jklingel 06-11-2010 11:22 PM

roof
 
Tough spot you are in. If it were me, I'd bite the bullet (you bought it cheap, right?) and re-roof it w/ some plastic insulation; spray, or board. Check w/ local codes, but you may be able to pull the shingles and lay 4'x8' sheets of 2" or 3" XPS (60 psi stuff) right on the roof, snug up against each other, covered w/ 2x4s lying flat and plywood/shingles over that. If that doesn't meet specs, then use 2x4s vertically and trimmed sheets in between. A bit of money, but then you have all that nice T&G exposed to view. Worth it? GL. j

phelix17 06-12-2010 01:32 PM

Quote:

Originally Posted by jklingel (Post 454944)
Tough spot you are in. If it were me, I'd bite the bullet (you bought it cheap, right?) and re-roof it w/ some plastic insulation; spray, or board. Check w/ local codes, but you may be able to pull the shingles and lay 4'x8' sheets of 2" or 3" XPS (60 psi stuff) right on the roof, snug up against each other, covered w/ 2x4s lying flat and plywood/shingles over that. If that doesn't meet specs, then use 2x4s vertically and trimmed sheets in between. A bit of money, but then you have all that nice T&G exposed to view. Worth it? GL. j

How is that then attached to the roof? That would be some long nails or screws?

jklingel 06-12-2010 01:54 PM

yes
 
Read here about the Remote Wall: http://www.cchrc.org/ They use up to 6" of XPS on the outside of walls. Glue the XPS down and screw the 2x4s. I don't see why that would not work on a roof with either 40 or 60 psi XPS, but I also don't know if anyone recommends this as a "suitable building practice". The first layer of roof sheathing should be warm enough to not get condensation on it this way, and putting the next sheathing over the 2x4s would give you an air gap for any water vapor that does sneak out to leave within. You will not have thermal bridging, either, as you would with 2x4s vertically and trimmed sheets of XPS between them. (Also, trimmed sheets never fit perfectly.) NOTE: Run this by a competent engineer, because I am not one. Greenbuildingadvisor.com is an excellent place to research and/or ask, too. GL. j

phelix17 06-13-2010 04:47 AM

Many thanks for the info. I will research.

TrafficCopSmith 06-14-2010 09:23 AM

Quote:

Originally Posted by jklingel (Post 455179)
Read here about the Remote Wall: http://www.cchrc.org/ They use up to 6" of XPS on the outside of walls. Glue the XPS down and screw the 2x4s. I don't see why that would not work on a roof with either 40 or 60 psi XPS, but I also don't know if anyone recommends this as a "suitable building practice". The first layer of roof sheathing should be warm enough to not get condensation on it this way, and putting the next sheathing over the 2x4s would give you an air gap for any water vapor that does sneak out to leave within. You will not have thermal bridging, either, as you would with 2x4s vertically and trimmed sheets of XPS between them. (Also, trimmed sheets never fit perfectly.) NOTE: Run this by a competent engineer, because I am not one. Greenbuildingadvisor.com is an excellent place to research and/or ask, too. GL. j

Thanks for the resource... I've been looking for something like this too.

Ron6519 06-14-2010 12:43 PM

Quote:

Originally Posted by jklingel (Post 454944)
Tough spot you are in. If it were me, I'd bite the bullet (you bought it cheap, right?) and re-roof it w/ some plastic insulation; spray, or board. Check w/ local codes, but you may be able to pull the shingles and lay 4'x8' sheets of 2" or 3" XPS (60 psi stuff) right on the roof, snug up against each other, covered w/ 2x4s lying flat and plywood/shingles over that. If that doesn't meet specs, then use 2x4s vertically and trimmed sheets in between. A bit of money, but then you have all that nice T&G exposed to view. Worth it? GL. j

Before you start loading up the structure, I would have a structural engineer do some calculations. The current structure was built with certain weight considerations, which I doubt took this into account.
Ron


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