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Old 11-29-2012, 10:14 AM  
nealtw
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This article talks about it.
http://www.inspectapedia.com/Energy/Roof_Venting_Need.htm



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Old 11-29-2012, 05:53 PM  
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If you don't want to vent the rafters, (as Andy Gump said), you need rigid or SPF (R-20) tight against the sheathing, then cavity insulation to meet your location's total R-value (R-38), see the chart map; http://www.buildingscience.com/documents/published-articles/pa-crash-course-in-roof-venting
The rigid foamboard requires canned foam at all edges for an air-tight seal. ADA the drywall to prevent air infiltration through any fiberglass/Roxul cavity insulation; http://www.buildingscience.com/documents/information-sheets/air-barriers-airtight-drywall-approach/

Gary



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Old 11-29-2012, 08:25 PM  
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GBR: If you look at the whole room. Massive amount of windows will be hard to heat the room. As cool as the windows make the room feel the area above the windows will be the warmest and adding more heat for comfort will make the ceiling warmer than normal. So with that in mind insulating with out a gap will require more insulation than can fit in the space. Evan if Drewdin puts foam board below the rafter as mentioned he will still have less over the wall above the windows which will have no insulation at all.
I beleive that "could" cause ice damming which would be bad enough for roof leaks and redo situation but with no headers over the windows the weight of an ice dam could also cause structural damage.
A little heat lose thru the ceiling may be good insurance when you think about one bad ice dam bringing down a structure.

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Old 11-30-2012, 07:29 AM  
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@GBR, would you recommend putting the rigid foam against the sheathing and then the roxul insulation? I planned on doing it the opposite way, roxul against the sheathing and then foam board. I have not mentioned it prior but the roof is a rubber in case that factors into anything. There is a 1" foam board and then its one giant sheet of rubber.

I don't plan on venting the rafters, it will take to much time and money that I don't have right now. I do plan on the Roxul R23 and a rigid foam board as I stated earlier. I will tape the foam board seams but its going to be hard to seal around the recessed lights.

I looked into spray foam and it would cost ~1500 to coat the area with 1", the foam board and roxul will cost $500. Its a no brainer...

I might get the DOW spray foam and seal under the recessed light and then add the roxul/rigid foam but thats only an R4.

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Old 11-30-2012, 08:42 AM  
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I also just realized that the electrician installed non-IC rated recessed lights in this area. Is this something i should have replaced? It would kill me to have 3" around each light that could not be insulated.

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Old 11-30-2012, 09:42 AM  
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I would want IC but I don't think you have room for them. Recessed lights are not a good idea here.

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Old 11-30-2012, 11:14 AM  
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Thanks neal, i hope i can make them work somehow.

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Old 11-30-2012, 05:00 PM  
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If nothing else you could flatten half of the ceiling, you would have room for the lights closer to the house wall.

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Old 12-03-2012, 07:26 AM  
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Hi neal, i got the electrician to replace the light fixtures with IC rated ones, on a side note. What do you mean when you say flatten half the roof? Thanks

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Old 12-03-2012, 08:39 AM  
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2x4s level from the house wall to about half way on the ceiling.



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