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Community and Q&A

Adding attic insulation

Darren Williams | Posted in Energy Efficiency and Durability on

zone 6 northern NH,single story house, low clearance in attic, only 4 feet at tallest point, so access is poor at best, ceiling is 6×6 beams with 1×10 boards on top of beams,boards are not tongue and groove and have gaps up to 1/2 inch between them, lots of unsealed electric boxes,wire runs, etc. current insulation is approx 10 inches of fiberglass batt on top of boards.there is a sheet of poly between the fiberglass and boards but it does not cover all the ceiling and has large cutouts at boxes so it is mostly useless, I know that this needs a complete overhaul with proper air sealing but in the short term would a layer of blown in cellulose on top of the fiberglass help with heating or is it just a waste of time and money for little or no gain? the roof has full length soffit vents and full length ridge vent with baffles in the rafter bays so there is plenty of ventilation.

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  1. GBA Editor
    Martin Holladay | | #1

    My usual advice applies: first do the air sealing work, then add more insulation.

    If access is tough -- too difficult for air sealing work -- you could consider installing a thick layer of rigid foam on top of the existing roof sheathing, followed by a second layer of roof sheathing and new roofing. If you go this route, you will need to seal the soffit vents and ridge vent (and also find a way to insulate the gable walls in the attic).

    Another possibility is to work from inside, and install an air barrier at the ceiling level, followed by more insulation and a new finish ceiling.

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