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Reducing heat loss from existing ductwork in an attic

headscratcher | Posted in Energy Efficiency and Durability on

I am a remodeling contractor in Connecticut attempting to come up with a thorough plan to eliminate the causes of ice damming and heat loss in a customer’s attic. Existing insulation is fiberglass batts (R-38?) pretty carelessly installed between the joists and compressed to 9″. The air handler and ductwork are in the attic and leaking like mad. Soffit and ridge vents are in place.
What I’m clear about doing-
1- Sealing penetrations in the attic floor.
2-Making a rigid insulation cover for the pull down stairs.
3- Covering the recessed cans (with 3″ of air clearance) and bathroom fans with insulated covers.

Once that’s all done and I’ve addressed the ductwork leakage I intend to have a blanket of fiberglass blown in (with baffles in place at the eaves and a walkway to allow access to the air handler).

My questions pertain to how best to seal and additionally insulate the ductwork.
The trunk lines are rigid fiberglass ductboard with insulated flex duct branching off to the registers.
Is there an easier but still effective way to seal the ductboard/flexduct joints than with foil tape and mastic? i.e. with spray foam?
And regarding the ductboard trunks and flex duct; any suggestions on cost effective ways to add insulation around and lessen heat loss from these?
Warm in the attic, Jim

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  1. GBA Editor
    Martin Holladay | | #1

    You list so many troublesome details -- pull-down stairs, recessed lights, an air handler, ductwork -- that it's hard to imagine that your plan makes any sense. You will end up spending a considerable amount of money and time, and you will still end up with a half-baked solution (with lots of heat leaks during the winter).

    I think that it will be cheaper in the long run, and much simpler, to create an unvented, conditioned attic with closed-cell spray polyurethane foam.

    For more information, see Creating a Conditioned Attic.

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