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Community and Q&A

Pink sill foam vs. green treated lumber

jackofalltrades777 | Posted in Building Code Questions on

On interior walls sitting on a concrete slab. Which would be better? Green treated lumber or standard lumber sitting on top of the pink foam sill sealer membrane?

The treated lumber has borate/chemicals in it while the foam sill sealer doesn’t put off VOCs.

Which works better, is longer lasting and healthier?

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  1. diynorth | | #1

    IMO, the pink sill sealer would be healthier and a fraction of the cost. I don't know which would last longer, but i would think either would last a good long time.

  2. Expert Member

    If you decide to use PT lumber anywhere in your build, make sure to specify MPS rather than ACQ so that you don't have trouble with fasteners corroding.

  3. GBA Editor
    Martin Holladay | | #3

    As long as your local building inspector isn't involved, this is your decision to make. Either way works (although some code inspectors may still insist on pressuure-treated plates -- so it's worth checking with your local building department).

    If you are concerned about the chemicals used in the pressure-treating process, use the sill-seal instead. I have never heard about any health concerns arising from the use of foam sill-seal.

    -- Martin Holladay

  4. Expert Member
    Dana Dorsett | | #4

    For interior walls on a slab that has a full polyethylene vapor barrier you don't really need either, especially if the slab has full-coverage insulation below.

    If it's on an uninsulated basement slab sans vapor barrier in a more humid but cool zone (US climate zone 4A or colder) a half-inch of EPS foam between the bottom plate and the slab would limit summertime uptake of room air moisture, whereas a foam sill gasket will not. Most foam sill gaskets aren't really great capillary breaks either. Any density of EPS would be fine for non load-bearing walls, but you'd need an engineering sign-off for load bearing walls.

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