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Community and Q&A

Attic Insulation options

Ben Reese | Posted in Energy Efficiency and Durability on

I am evaluating the options on upgrading the insulation on my lake house. The house is in Zone 5 (hot and humid) and the main concern in improving the comfort and efficiency in the summer months. The ceiling has blown insulation about R 30. The air conditioner and ducting are in the attic on the west side of the building. To improve the heat in the attic I am looking at insulating at the roof line. The two options are blown foam in the roof or ridged foam board with foil wrap. I have been told that foam is problematic with older asphalt shingles due to increase heat at the roof line. The ridged foam can be attached under the roof rafters to form a solid air tight attic. The space below the roof deck and above he ridged foam would be vented from the soffits to the vents in the roof peak. This would allow some heat relief for the shingles.
I need to determine if the ridged foam is feasible or advisable.

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  1. GBA Editor
    Martin Holladay | | #1

    The best approach (if you want to create a sealed, conditioned attic working from the inside) is to install closed-cell spray foam.

    For more information, see Creating a Conditioned Attic.

  2. Nick T - 6A (MN) | | #2


    Since you mention that your HVAC is in a limited area possibly and the cost of spray foaming being so high.

    Would it be possible to build a small foam board structure over the hvac area? Could just build a frame with 2x2's or 2x4's and then sheath it with a foam board and maybe top with a fresh coat of blow in. Just an idea - any time you can take an energy conservation measure from thousands of dollars to hundreds... makes payback and implementation rates improve.

    Depending on your budget and amount of freetime/ambition - it might not be worth it... but typically the payback is MUCH better when DIY is an option.

  3. Ben Reese | | #3

    Thanks for the response, My concern on the spray foam is the potential for damage to the asphalt shingles. I am not sure how real that problem might be. The ridged foam board does allow air flow under the roof deck.

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