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Old 01-25-2016, 11:05 AM   #1
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Finishing Attic Space - Best Insulation Plan?


Hello,

I'm planning to convert my unfinished attic space into an entertainment room. It has a cathedral ceiling, knee walls and flat ceiling. Spray foam would be too costly so I'm looking at fiberglass.

The current plan is:

Cathedral (2x10) - Vent baffles with R38 faced fiberglass batts
Flat Ceiling (2x8) - R-49 faced fiberglass batts
Exterior Walls (2x4) - R15 faced fiberglass batts
Kneewalls (2x4) - Roxul Safe n Sound (to keep noises from entering bedrooms below)

The attached plan shows it better.

I'm wondering if and where this plan could be improved. Maybe with rigid foam board or building exterior walls to 2x6 depth, preventing thermal bridging, etc.

I want this space to be comfortable. Thank you!
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Finishing Attic Space - Best Insulation Plan?-behind-kneewall.jpg   Finishing Attic Space - Best Insulation Plan?-exterior-wall.jpg   Finishing Attic Space - Best Insulation Plan?-flat-ceiling.jpg   Finishing Attic Space - Best Insulation Plan?-kneewall-cathedral.jpg   Finishing Attic Space - Best Insulation Plan?-kneewall-meets-cathedral.jpg  

Finishing Attic Space - Best Insulation Plan?-plan.jpg  
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Old 01-25-2016, 12:59 PM   #2
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The staple in baffles aren't that good. If it were my home and ridge vented, I would create a continuous vent space with rigid foam (foil face works but Gary has previously brought up a good point about unforeseen melting at the bottom), fill the remaining void with fibrous insulation and drywall where necessary.

I would leave that knee wall area as conditioned as well.

http://www.finehomebuilding.com/pdf/021221068.pdf
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Old 01-25-2016, 01:33 PM   #3
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Thanks for the quick response.

Good point on creating the rigid foam vents. So don't use foil faced rigid foam? If I use fiberglass batt Insulation it should still have face right?

My thought on the area behind the kneewall was to keep it like my garage. Insulated but not conditioned. So ductwork would be subjected to less extreme temps, but less work for my hvac.

Are you saying to not insulate the kneewalls and keep it all conditioned?

Thanks for the help!
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Old 01-25-2016, 01:54 PM   #4
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Insulate down the plane of the roof so that the kneewall area is effectively inside the conditioned space. At that point, the duct work will be a more hospitable location and you could supply a bit of condition air and return air to that space with a small opening on both the supply and return side.

As far as facing on the insulation, we don't really need it in this area either way.

The foil facing is fine and I actually like it, however, Gary brought up a good point of the radiant aspect of the foam creating a melting issue down near the eaves. If you want, you could run bare insulation near the eaves and radiant/foil faced further up if you want.
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Old 01-25-2016, 02:01 PM   #5
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Thanks for the help!
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