Locating ducts in attic underneath a thick layer of cellulose
Building a two story house with basement in climate zone 5A. Attached to the "main" portion of the house is a one story "wing" with a laundry/mudroom and the garage (this portion is built on slab...insulated with EPS to ~R-22). Walls are R-48. Raised heel (16") trusses in the attic with blown cellulose to at least R-60.
My plan was originally to keep all ductwork to the slab "wing" inside the conditioned envelope and soffit around the ducts.
Problem is - - - I neglected to share this particular detail of the house construction with my wife. I let her know about this plan today and she let me know that she dislikes soffits.
So now I'm looking at solutions to make her happy. My realistic options are probably as follows.....
1.) Maybe go with exposed duct work. This is the lesser of two evils (soffit versus exposed) for her if the ducts MUST stay in the conditioned envelope.
2.) Turn the attic into conditioned space by use SPF on the underside of the roof deck. This isn't my favorite option due to the huge cost involved.
3.) Install the ductwork in the attic.
I'm leaning towards option #3 and wonder how big of an efficiency penalty would result. If all ducts were insulated and well sealed and run against the bottom cord of the 2x4 trusses.....
I thought of it this way. At R-3.4 per inch and hitting R-60 minimum I'm going to be blowing this stuff in 18" deep minimum. A 4" duct insulated to R-6 sitting on a 2x4 truss will still have about R-36 of insulation between it and the air above the insulation.
While obviously not the same as keeping the ducts below the ceiling, I think there wouldn't be a huge energy penalty....and it keeps the wife happy.
Any input, advice or other ideas are appreciated!
Posted Tue, 05/20/2014 - 00:45
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