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Are two layers of XPS separated by T1-11 OK?

Braden Enroth | Posted in Energy Efficiency and Durability on

I am re-siding my attached heated garage with wood clad siding to match the house. The current siding, T1-11 (plywood siding), will not be removed as I need to side over the top of the T1-11. Because the windows and doors are reset to a plane that matches the house, I need to use two-inch thick strapping over the T1-11. Instead, I am considering adding 1 inch of XPS over the T1-11 and using one-inch strapping. Since the current insulation is 3 1/2 inch fiberglass with one inch of XPS as sheathing under the T1-11, I am concerned if adding another layer of XPS over the top of the T1-11 will cause a moisture problem. Our climate is cold (zone 6) in Wisconsin. Please reply with your thoughts. Thank you.

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  1. GBA Editor
    Martin Holladay | | #1

    I don't think that your plan will cause any problems, as long as you pay attention to your flashing to manage exterior moisture (rain).

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