Has anyone mixed open and closed cell in a roof assembly?

[Terry Fong]

I have heard some builders talk about doing a flash and batt style approach but with open cell over a thin closed cell layer. Has anyone tried this and what were the results on blower door tests?

[Derrick Washington]

Yeah we do flash-and-fill a lot. 1-2 inches of closed cell first for vapor control and air sealing, then fill the rest with open cell. It is cost-effective since closed cell is pricier.

[Jennifer MacAllister]

We have gotten great blower door results with this approach. Under 1 ACH50 on most of our jobs. The key is making sure that first layer of closed cell is continuous with no gaps.

[Rick Deluca]

Interesting approach. Do you ever run into issues with adhesion of the open cell to the closed cell layer?

[Derrick Washington]

Not really if you apply the open cell while the closed cell is still within its cure window. If closed cell has fully cured you want to rough up the surface a bit first.

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