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Unfinished walk-up attic: best way to get ducts into conditioned space?

aunsafe2015 | Posted in General Questions on

Climate zone 4 (central NC).  I want to bring the HVAC ducts in my unfinished walk-up attic into conditioned space, which I think basically means I want to insulate the walls and roof deck of my attic.  Goal is to preserve ability to finish the attic somewhere down the road, but that might not happen for years (or ever), and I’d rather bring my ducts into conditioned space as soon as I can.

I had previously been planning on spray foam, but I’ve become increasingly uncomfortable with the (small) possibility of being one of the unlucky few who has odor/toxicity issues.

Based on attached pictures (I know, the ductwork is terrible), is spray foam basically my only reasonable option?

Rafters are 2×8, so I thought about having the depth expanded and using baffles & fiberglass (or rock wool).  A challenge with that, however, is that as shown for example in picture 2, there are certain portions of my roof deck that do not extend to a soffit vent due to roof features like dormers.  My understanding is that every rafter bay needs to be vented.  So does that basically kill (or greatly impede) the furring + baffles + fiberglass option?

Would building a knee-wall around the ducts and covering them with blown-in cellulose or fiberglass do any good?

Are there any other non-spray foam options that a typical contractor would have the skills to do?  If anybody has insulation contractor (spray foam or otherwise) recommendations in the Raleigh/Durham area please let me know.

Thanks for any input.

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  1. 300TTto545 | | #1

    Central NC here also. Frustratingly new house I see but very common around here. I tour houses a fair bit and have never seen ducts in conditioned space without foam..
    You have a radiant barrier which at least helps a bit with the duct gain in the summer. The value of that radiant barrier goes to zero if you were to foam the rafters so it is one more (small) strike against that option. .
    I am no expert on the correct option. Know that ducts in the attic certainly aren't ideal but chasing the losses isn't always worth it. Have you had an energy rater come by? Have you had the ducts checked for leakage (Energy star at build time would have done this)?
    My personal feeling is to make sure the leakage is decent. You can feel around the ducts - I find the summer better demonstrating small leaks. This is low hanging fruit. You then could start framing out areas that would be anyway and using blown glass.
    Know that you are chasing 15% probably. That maybe $50 a year or less - so keep some perspective. And that would be 15% just on your upstairs costs.
    I can tell you many times, putting some solar panels on the roof has a better ROI than trying to seal the attic (in our climate).
    Fully covering the ducts in blown glass is now considered acceptable. I just built a NC HERO (High Efficiency Residential Option) code compliant house. My HERS is 57 and -7 with solar. We have ducts in the attic - covered completely in blown glass. They blow cool when compressor first turns on - not hot like the last house we had with your exact arrangement (radiant barrier, modern R8 duct insulation, vented attic).

  2. GBA Editor
    Brian Pontolilo | | #2

    Hi Aun.

    I suggest you read these two articles. They should answer all of your questions:
    Creating a Conditioned Attic
    How to Build an Insulated Cathedral Ceiling

  3. Expert Member
    Akos | | #3

    You can spray foam the trouble areas only. If you go with a flash and batt approach there, only enough SPF for condensation control, the rest fluffy, it would not cost all that much.

    Looks like most of your roof can be easily vented.

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