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Insulation strategy with Open Web Trusses

lbaker222 | Posted in Energy Efficiency and Durability on

Hi everyone,

I’m working on a new construction house in California (CZ5) in the mountains where snow is also a factor. 

Originally I had proposed a roof assembly (see first photo) with R-38 Comfortbatt Rockwool in the cavity and and 6″ of Rockwool Comfortboard (R-24) on top of the roof deck. 

Now the structural engineer wants to change to 18″ D open web trusses (see second photo) and I’m a little stumped about what to do with the insulation strategy. I don’t want to fill the whole 18″ cavity with insulation and have my proportion of rigid insulation be totally out of whack. But I think the open web design will make it a challenge to keep the insulation tight to the sheathing. The owner also wants to avoid spray foam if possible, although if we need to I’m sure I could convince him.

Not sure if I’m thinking about everything correctly. Appreciate any advice. Thanks!


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  1. Expert Member


    If you go with parallel chord trusses you can use a vented roof assembly and eliminate the costly and complex above sheathing rigid insulation.
    See assembly #1 in this link:

    1. lbaker222 | | #2

      Hey Malcom,

      Thanks! I've been getting pretty far in the weeds learning about all the advantages of exterior rigid insulation that I failed to see this more simple option. Thank you!

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