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Wed, Jun 8, 11 at 16:45
| So my builder wants to spray foam all the rafters in my attic. We live in new england and will have 1 finished attic room (guest room). Maybe use the other room for storage and HVAC. Out house has a ground floor, second floor and an attic floor.
With the finished room being occasional use, and given this is very limited info. Would spray foam in the attic help the main living space? All the other walls we have preexisting blown in cellulose and batt. |
Follow-Up Postings:
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- Posted by Renovator8 (My Page) on Wed, Jun 8, 11 at 17:41
| It is possible that closed cell foam is the only way to achieve the building code required min. R value without furring the rafters and losing headroom. Can't say more than that without seeing the design. |
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- Posted by energy_rater_la (My Page) on Wed, Jun 8, 11 at 17:44
| spray foam is a good thing, when it is correctly installed. an unvented attic (foam @ roofline) puts ductwork in a semi conditioned space, and really adds to the air tightness of the house. read thru a few posts about upstairs being hot/cold and you will see what difficulty folks have with comfort in rooms that are built in attic space. the problem is the air leakage and heat/cold gain from attic space into these rooms. the walls, the floor and ceiling of these rooms are all surrounded by attic temp air. when you move the thermal boundry to the roofline, and make it air tight then the leaks in the walls ceilings and floors are not pulling extreme attic conditions into the house. things like recessed cans, oversized cuts at bath fans and even duct leakage become less of an issue because the air and thermal boundry is at the roofline. visit www.buildingscience.com and look for unvented attics for your climate. best of luck. |
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| If the room/room in the attic isnt used too much, nor is it a priority when the whole house is taken into consideration, and with the assumption everything will be done correctly. In general, could/will the rest of the house (all the non attic rooms) benefit from spray foam? |
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- Posted by david_cary (My Page) on Thu, Jun 9, 11 at 4:47
| If the HVAC is up there, you will see a whole house benefit. Whether it is worth the cost is another question but you will definitely see a benefit. It is also unlikely that you have adequate attic insulation already so this will just add to your effective attic insulation. |
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- Posted by Renovator8 (My Page) on Thu, Jun 9, 11 at 7:52
| Will there be insulation in the floor between the guest room and the main living spaces? If so, how much? |
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| what kind of spray foam? open or closed? I typically never recommend closed foams in rafters as it prevents the water from coming through if there was a leak in the roof. With closed cell, your roof could be leaking and you will never know it until your sheathing rots away. Open cell will be cheaper as well, with a slightly less r per inch. |
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- Posted by energy_rater_la (My Page) on Thu, Jun 9, 11 at 11:38
| Yes the rest of the home will benefit as well. I also recommend open cell less R-value means you have to put more, but on the roofline unless you have a cathedral ceiling this isn't an issue. ROI is higher, but still much less than if you had |
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