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Old 02-18-2012, 11:05 PM   #1
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Insulating open rafter ceiling


I am remodeling a ranch house with open rafter ceiling (after removing ceiling joists). I like the look of the roof rafters and I am trying to figure out how to insulate. My plan is as follows:

1. install 2" thick or 2 x 2" thick rigid foam insulation, with a 3/4" air space between the deck material between the roof rafters.
2. Install 1/2" thick gypsum board over the rigid insulation, with possible nailing surfacefor gypsum board which would give me another air space
3. I want to expose at least 1/2" or 1" of the roof rafters, whidh will stick out of the gypsum board finish.

I might not have enough R value for the insulation, but I plan on redoing exterior roof and might add additional insulation on outside.

Does anyone see any problems with this method?

thank you for any feedback

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Old 02-19-2012, 12:43 AM   #2
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Insulating open rafter ceiling


I am a bit stunned...

...you removed your ceiling joists?

Are you aware that you might have compromised the structural integrity of your house by doing this?

Unless your roof rafters are attached to a ridge beam (not a ridge board) your walls may at some time bow out and the roof system come down.

And yes, I can envision other problems with your insulation scheme but you are not providing enough information on that account.

Andy.

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Old 02-19-2012, 12:48 AM   #3
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Insulating open rafter ceiling


You probably shouldn't have done that. Are your walls still straight?
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Old 02-19-2012, 06:10 AM   #4
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Insulating open rafter ceiling


I have a wall under the ridge board, stiffened with plywood and also added metal ties that connect rafters to vertical surface. My walls are straight and I don't see how the walls would bow out.

What problems could I have with my insulation scheme?
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Old 02-19-2012, 10:04 AM   #5
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Insulating open rafter ceiling


You needed a ridge beam. not a ridge board. Big differance.
Before you go to far with this how about some pictures.
No one here has any reason to cut down your idea, but without making provisions to stop those walls from bowing out there's going to be trouble down the line.
Those hurricane ties you installed are to stop roof up lift not the stop the rafters from forcing the walls out.
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Old 02-19-2012, 10:25 AM   #6
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Insulating open rafter ceiling


I have buid a bearing wall under the ridge board, which sits on a bearing beam below. Then I have plywooded the wall and now I'm adding metal ties to keep the exposed rafters attached to wall. See pic

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Old 02-19-2012, 10:36 AM   #7
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Insulating open rafter ceiling


Alternately, if you guys think this doesn't work, I can put back joists at 48 OC and leave them exposed
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Old 02-20-2012, 12:47 AM   #8
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Insulating open rafter ceiling


I would get a building permit for the structural changes made. Just for the full bearing aspect of your plan and the required reinforcing the support of the wall below,through the joist-space with solid blocking, in the basement/crawlspace to the earth.
Your AHJ may require engineering.

The rafter ends may require covering as they are not beams or logs with a different fire-rating than wood light-timber framing. Code requires minimum 1" air-space, and that's like a "D" on a school test...... Going with foam on the roof deck later will be worthless with the air-space you will have from now, choose one or the other. Hot roof or cold roof. http://www.buildingscience.com/docum...rchterm=attic+

http://www.buildingscience.com/docum...d-roof-systems

Gary
P.S. You may need solid blocking under the plywood wall to transmit forces from the roof to the ground, they appear to be missing. It could be my eyes...LOL. Looks to be an opening with ridge board unsupported, too.

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