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UN-treated bottom plate

UN-treated bottom plate

UN-treated bottom plate

I have been asked to look at a remodel project that includes wood framed load bearing walls (IBC 2012). The walls have been located and constructed over the existing vinyl tile that covers a conventional slab on ground foundation. The builder did not use pressure treated bottom plates and insists that they are not required since the wood is not in direct contact with the concrete. I have seen many cases where older construction has a sheet metal termite shield between suspended concrete framing beams and wood (untreated) floor framing. Granted, it was pre ICC construction, but my question is:

If the wood bottom plates are not directly in contact with the concrete foundation, can I state that the lack of a pressure treated bottom plate DOES NOT meet code.

Thanks in advance to the forum for your views on the subject.

RE: UN-treated bottom plate

I may be wrong here but I thought the treated plate was just to avoid absorbing moisture from the concrete. I'm not sure I see a big issue with using an untreated 2x in a conditioned location where the slab has had ample time to 'dry'. Then again I'm not sure what the code interpretation is either.

I know this is not answering your question, sorry about that.


RE: UN-treated bottom plate

The code does allow untreated plates on concrete if there is building paper in between the two. It could be argued that the vinyl tile substitutes for the building paper.

Regardless, i would not do it.

Mike McCann
MMC Engineering

RE: UN-treated bottom plate

I agree with msquared. IF the vinyl tile can be proved out to be a "vapor barrier" of the required class then it might suffice. It might actually be better than "building paper":). The issue of drying is not quite accurate. The issue as I see it is the thermal mass of concrete makes it a lightning rod for moisture condensation. In addition a SOG will have pretty good vapor drive from the ground below unless there is a good vapor barrier underneath that is not decayed/sealed/damaged/too thin/etc.

Putting a Structural wall on top of a vinyl floor... what will those crazee carpenters do next! Must be a real quality crew.


RE: UN-treated bottom plate

The purpose for using pressure treated lumber in contact with concrete is that concrete is often in contact with moist environments and will permit moisture to travel through it. This causes a damp interface that can and has led to rot conditions in the bottom plate.

The vinyl floor should effectively preclude the moisture issue and would function in a manner similar to the use of a PEVB or building paper...


RE: UN-treated bottom plate

Per the 2012 IBC
"2304.11.2.4 Sleepers and sills.
Sleepers and sills on a concrete or masonry slab that is in direct contact with earth shall be of naturally durable or preservative-treated wood."

It only states that if the slab is in direct contact with the earth, not whether or not the sleepers and sills are in direct contact with the slab. You might have to go to the AHJ for what they want on this.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

RE: UN-treated bottom plate

Thanks to all for your responses.

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