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Old 07-04-2012, 11:20 AM   #1
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Insulate attic walls that are against finished area


We have a large attic space that has one of the gable ends against the main house wall, this space gets very hot and cold, right now its 120 degrees in here... the wall it shares with the house of course warms up and heat radiates into the finished space.

the builders just stuffed R-19 fiber glass into the 2x4 wall, which doesn't fit well..

I am going to be replacing this with R-15 Roxul insulation since it deadens sound much better (the attic space works like a resonance chamber and amplifies road noise a bit)

after that I wanted to cover the wall with some type of insulated sheathing... was thinking Polyisocyanurate panels. would this be alright? that would add another R-10 and stop any bridging of heat and cold

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Old 07-06-2012, 01:40 PM   #2
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Insulate attic walls that are against finished area


no comments? :\

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House Information: Build 1996, 1500 sq ft basement, 1500 sq ft 1st floor, 800 sq ft 2nd floor, 560 sq ft unfinished attic space on 2nd floor. Insulation: Attic blown fiberglass, walls R-19, Basement R-19. HVAC: Trane xc95m fully modulating furnace, single zone, Trane XL20i commiunicating AC unit, TCONT900 Communicating thermostat.
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Old 07-06-2012, 01:57 PM   #3
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Insulate attic walls that are against finished area


the polyiso on the attic side? If so, that works thermally, but not for fire codes. You'll need to cover it with an ignition barrier or get a building official to sign off on it being left exposed. An ignition barrier could be plywood, sheet metal, or gypsum board...
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Old 07-06-2012, 02:09 PM   #4
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Insulate attic walls that are against finished area


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the polyiso on the attic side? If so, that works thermally, but not for fire codes. You'll need to cover it with an ignition barrier or get a building official to sign off on it being left exposed. An ignition barrier could be plywood, sheet metal, or gypsum board...
yeah, it will be drywalled over, what I am more worried about would be what about it being faced, or in some cases it being sheething, one side is a reflective barrier, not sure on the specifics of where that is allowed to be placed or not..

energy auditor mentioned some of the newer houses around us where built with a reflective barrier used inproperly but forgot to ask how or why...

any ideas on what to do and not to do?
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House Information: Build 1996, 1500 sq ft basement, 1500 sq ft 1st floor, 800 sq ft 2nd floor, 560 sq ft unfinished attic space on 2nd floor. Insulation: Attic blown fiberglass, walls R-19, Basement R-19. HVAC: Trane xc95m fully modulating furnace, single zone, Trane XL20i commiunicating AC unit, TCONT900 Communicating thermostat.
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Old 07-06-2012, 06:49 PM   #5
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Insulate attic walls that are against finished area


Without being there and seeing, first hand, all variables I cannot give you a definitive direction here. I will say that many people have done what I think you're doing without any adverse effects....

If you take a section at a specific point in your wall you may find double barriers and all that mess, but it's really the system as a whole that needs to be looked at. Laboratory analysis only goes so far before mother nature plays a hand...
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Old 07-07-2012, 08:35 PM   #6
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Insulate attic walls that are against finished area


1. Do you have a vapor barrier poly sheeting inside?

2. Is it just asphalt paper faced f.g. batt insulation? OR no facing at all? OR cellulose insulation?

3. Is the drywall air sealed (ADA)? How old is the house?

4. Why foil-faced or other, looking for the radiant aspect?

Gary

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