Open Cell roof deck or attic floor

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Open Cell roof deck or attic floor

Done my research, open cell foam is my preferred choice. Building a 3,300 sf house in Fort Worth TX. Pitch of roof is steep 12@12. House is single story. Considering the following two foam options, would appreciate feedback. Additional info, going with two a/c units (4 and 2 ton, both units are two stage. Also using erv air exchange to supply fresh air.

Option A) Open cell foam 5.5 inches under the roof deck, 3.5 in walls, both hvac blowers are in attic. This will provide the closed envelope conditioned attic model. However because of roof slope, creating more surface area for roof deck foam than normal, translates to more $ for foam. Roof deck will be standard OSB.

Option A Benefits:
HVAC running in conditioned space.

Option B) Open cell foam 5.5 inches on attic floor, and 3.5 in walls. Same scenario with hvac blowers (in attic). Non-conditioned attic here, but on this option I'll go with "OSB-radiant foil backed" for roof deck to help keep attic temperatures down. This option also give me the ability to add 5-10 inches of blown in cellulose on top of attic floor foam if I feel necessary in future.

Option B Benefits:
All ducts, vents and electrical housings cut at ceiling drywall are sealed with foam
Less expensive to foam attic floor than roof deck
I'm not having to condition my attic space.

Ok guys, A or B?

Thanks.

Asked by Jeff Bailey
Posted Sat, 12/29/2012 - 20:25
Edited Sat, 12/29/2012 - 20:45

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