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Community and Q&A

Cellulose on Attic Floor and Closed-Cell Spray Foam Between Rafters

1869farmhouse | Posted in General Questions on

Looking at another house last night and noticed that they’d had approximately 2 inches closed cell foam sprayed between the rafters in the attic, but there was still a solid 4-5” at least of old brown cellulose  on the attic floor.

I’ve never run into this before.  Does it cause problems?

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  1. GBA Editor
    Kiley Jacques | | #1

    I'm giving your post a bump. Here's an informative discussion about cellulose used in combination with closed-cell spray foam, albeit in walls: combination insulation.

  2. Expert Member
    Michael Maines | | #2

    Austin, it can be fine to combine insulation types in a flash-and-batt or flash-and-fill assembly, but with the insulation in direct contact with each other. In general, it's hard to predict what will happen in interstitial spaces that are not fully indoors or outdoors--partway between indoor and outdoor temperatures, often tending toward whichever one has higher humidity, and bad things can happen. Bad things don't always happen, but the closer together you can get your air, vapor and thermal control layers, the more predictable the assembly will be.

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