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Community and Q&A

What is the best option for insulating a vaulted ceiling?

Robert Suignard | Posted in Energy Efficiency and Durability on

Hey guys this is my first question ever on any forum so let me know if i need to supply mor info or not and i’ll apologize in advance if i sound stupid because i’m far from carpenter. I live in northern saskatchewan and am building a new 1500 square foot home. I have had it in my mind from the begining of the build i wanted to use spray foam to insulate the house because i am heating the house with an electric forced air furnace and want it pretty tight. The problem is there is a vaulted ceiling in part of the house and I’m not sure what is the best way to insulate that part of the house and i’m a little confused on my spray foam options besides spraying six inches of foam to get close to my r40 value i need. I also kinda wanted to know if i’m wasting money if spray foaming the walls and using convention fibreglass in the attic space.

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  1. User avatar GBA Editor
    Martin Holladay | | #1

    The best way to insulate a sloped (cathedral) ceiling is with rigid foam insulation installed above the roof sheathing. More information here: How to Build an Insulated Cathedral Ceiling.

    You wrote, "I also kinda wanted to know if i'm wasting money if spray foaming the walls and using convention fibreglass in the attic space."

    The problem with installing spray foam insulation between studs is that you still have thermal bridging through the studs. There are better approaches, including:
    - Double-stud walls
    - Walls insulated on the exterior with rigid foam
    - Walls insulated on the exterior with mineral wool.

    The problem with fiberglass batts installed on an attic floor is that they are the worst-performing insulation material available. Cellulose is preferable.

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