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Community and Q&A

Vaulted ceiling insulation

Beverett09 | Posted in Energy Efficiency and Durability on

Remodeling a home outside Chicago. Vaulted ceilings. 2″ x 6″ rafters. What are my options for insulating the ceilings?

1. Closed Foam? Expensive

2. 4″ Rmax foam board?

3. 2″ Rmax foam board and closed Foam spray? 

4. 1.5″ rafter furring strips and batt insulation?

Thank you in advance for your help.

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  1. GBA Editor
    Brian Pontolilo | | #1

    Hi Beverett09.

    A vaulted ceiling can be insulated with lots of different materials. What's more important to work out is the assembly. For example, a vented assembly can be insulated with fibrous insulation, but it may be tricky to reach R-49, a good minimum target R-value for your area. An unvented assembly typically has at least some air-impermeable insulation, either above or directly below the roof deck, and these assemblies are often built with a combination of materials. You also need to consider dew point control, vapor control, and air sealing. In other words, these are complex assemblies and are very important to get right. I suggest reading this: How to Build an Insulated Cathedral Ceiling

    1. Beverett09 | | #3

      Local code R30 value for vaulted ceilings. The roof is currently vented in the soffit. 4/12 pitched roof.

  2. Expert Member
    BILL WICHERS | | #2

    If you use rigid foam, you want to put it on top of the sheathing. 2x6 rafters don’t give you enough space to build this as a vented assembly and get sufficient insulation to fit. Even with a full fill of closed cell spray foam you’ll barely be able to get to R38, and there will be a lot of trimming needed — normally you don’t do a full fill of ccSPF to avoid the need for trimming.

    I would put rigid foam above the sheathing and use batts between the rafters inside. The article Brian linked shows how to essentially retrofit a vent gap if you want to go that route.


    1. Beverett09 | | #4

      Local code R30 value for vaulted ceilings. The roof is currently vented in the soffit. 4/12 pitched roof.

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