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What is best option to insulate Zone 5A attic?

9HPiFHWRiQ | Posted in Energy Efficiency and Durability on

I live in W Hartford, CT (Zone 5A) and have an attic that needs insulating.
I assume the insulation will need to be in the 2×8 rafters since we have AC
ductwork running thru the attic space and some batt insulation in the attic
floor covered by wood.  We have a new roof with a ridge vent and no vents in
the eaves as the roof has no overhang.  We have had issues with ice dams
given limited insulation in the eaves.

I would appreciate information the best way to solve.  We have been
a- spray foam in rafters (closed cell vs open cell?);
b- rigid foam in rafters with careful taping/sealing;
c- rigid across rafters and sealed, with cellulose packed in behind; or
e- no foam — cellulose in rafters, maybe gussetted down for more depth
(though ideally would not lose attic space).

Insight appreciated.  Thanks.

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  1. SLSTech | | #1

    The best overall system? Closed Cell between rafters & on all the walls, but you need to block off the ridge & gable (?) vents
    Open cell requires a vapor barrier to be sprayed on & both OC & CC may require a fire retardant or drywall to be applied

  2. GBA Editor
    Martin Holladay | | #2

    There is no "best" system. Whichever method you choose, be sure to install AT LEAST the minimum code R-value for your climate zone (R-38). That means about 6 inches of closed-cell spray foam or 10.5 inches of cellulose.

    Here's an article with more information: Creating a Conditioned Attic.

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