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Discussion Starter #1 (Edited)
Hi: This is my first time posting on this site although I have been here many times as there is a wealth of information here. My question is I am getting my shingles replaced and I live in an older storey and half house with knee walls and part of my roof is my ceiling. The attic is a finished bedroom and the only insulation I have is what is in the cavities of the rafters above. It is like a catherdral ceiling. All the the insulation I have is what is between the rafters, about 4" which has been there for at least 30 years. What I am planning on doing is when the contractors replace the roof I am going to get them to remove the old insulation by removing some of the roof boards and use spray foam from the top as a replacement which will give me more bang for the buck I think. The question I have is one contractor says no problem in using foam and spraying from the top and leaving an air gap between spray foam and sheeting. The other contractor seems hesitate on wheather you can do that and still leave a nice air gap. Who is right? I was planning on putting on a steel roof over this but I am now considering shingles as cost is rising. Right now I do have some problems with ice daming and the uspstairs is cold in winter and hot in summer. Any other thoughts on this project is appreciated. Thanks
 

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Going to have to go back and add your location to your profile.
Must be missing something, of this is not a finished attic why would you insulate the rafters?
Should be insulating the ceiling to seal the conditioned envelope not the roof.
Ice dams are caused from heat escaping the ceiling and outside wall area and lack of venting of the roof.
An unfinished attic need to be close to the outside temperture.
http://www.energystar.gov/index.cfm?c=home_sealing.hm_improvement_insulation_table

4" sure sounds thin anyplace in the US.
 

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Discussion Starter #3
Sorry, This is a finished attic which is a bedroom. The only attic I have is the roof rafters. It is like a catherdral ceiling. You are right it is not a lot of inslation but I can not add to like a conventional unfinished attic. I can only insulate in the cavity of the rafter that why I am wondering about replacing with spray foam which is a higher R value/ in
 

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We have only foamed that space from the interior side, but I don't see why it could not be done from above. It will offer the best r-value for the situation. Other option would be dense packing cellulose from the interior... as Joe mentioned, you will want to check on your local codes etc first.
 

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Discussion Starter #5
So you are saying a professional foam sprayer can lay down a layer of foam farily consistently. For example lay down 2" of finished foam and leaving a gap of about 1" to 2" for ventalation? I know foam just expands so much and in the end you may have to trim it but in my case that is not going to work, I need that air space.
 
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