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Community and Q&A

Pressure Treated Lumber on Concrete SubGrade Cellar Floor

Fi7df8CZ9x | Posted in Green Building Techniques on


We are about to frame up a wall on a fully subgrade cellar floor. Because of moisture and humidity concerns, we will be using metal framing and dense-armor wallboard… BUT:

For the bottom plate for the wall studs: Is it ok to use TREATED lumber?

Need I be concerned that the lumber (even though it’s treated) will eventually rot and become moldy since it is in direct contact with the concrete floor?

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  1. jklingel | | #1

    Michael: Would it not be advisable, on a couple of fronts, to address the water problems first? If you are worried about treated lumber rotting, it seems to me you have a pretty serious water problem. Any way to address the water?

  2. GBA Editor
    Martin Holladay | | #2

    According to the 2006 IRC (section R319.1), "Sills and sleepers on a concrete or masonry slab that is in direct contact with the ground" require "protection from decay ... by the use of naturally durable wood or wood that is preservative treated..."

  3. Fi7df8CZ9x | | #3

    Actually - There is no direct water problems... I am just worried about water vapour, general moisture and humidity leeching up from inside the concrete floor..

    Am I just being crazy?

  4. davidmeiland | | #4

    I would put a capillary break under a pressure-treated 2x bottom plate. Buy "sill seal" at the lumber yard, and staple a full-length piece to the bottom of the sill before you set it on the floor.

  5. Fi7df8CZ9x | | #5

    Also, i guess i have condensation concerns too, perhaps...

  6. gusfhb | | #6

    My 40 year old house has undamaged non PT right next to the new PT walls

    I would be more concerned with the PT eating the steel.

    Again, if you have this much moisture....

  7. wjrobinson | | #7

    Dryrotted wood near or in contact with concrete. That is what I find in many a crawlspace or cellar. All looks good many times till the rot shows up when like yesterday I pulled wire staples out which took no effort to remove. Some ice pick stabs showed that most of the non pt sill was well on its way to rot destruction. Pt wood is so inexpensive and worth using. Capillary breaks add protection too along with vapor barriers on one side or the other of all concrete used in forming walls and slabs of whatever foundation a home is built upon.

  8. gusfhb | | #8

    To be clear, I am not advising against the PT, but against the steel, or at least for an appropriate detail.

  9. davidmeiland | | #9

    I haven't seen corrosion issues with galv steel and PT in situations where the wood dries and stays dry. In the OP's situation the bottom plate will be dry, assuming he uses a capillary break and doesn't have flooding. PT used for framing a deck is a totally different situation.

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