I've always been told that the sole plate must be pressure treated, when in contact with concrete. I found section 317.1 in the IRC, but it only seems to address "sills and sleepers". It also states that the members only have to be PT, if not separated "from the slab by an impervious moisture barrier.".
Based on the code I've found, I'd say there's no requirement for the sole plate to be PT. Even if it was shoehorned into this section, putting an impervious moisture barrier between the sole plate and the concrete would meet the requirement.
I used untreated wood and installed sill gasket under the walls, when I added framing to my basement. Though it was just a couple dividing walls, so it was never inspected.
International Residential Code 2012
Chapter 3 Building and Planning
Section R317 Protection of Wood and Wood Based Products Against Decay
R317.1 Location required.
Protection of wood and wood based products from decay shall be provided in the following locations by the use of naturally durable wood or wood that is preservative-treated in accordance with AWPA U1 for the species, product, preservative and end use. Preservatives shall be listed in Section 4 of AWPA U1.
- Sills and sleepers on a concrete or masonry slab that is in direct contact with the ground unless separated from such slab by an impervious moisture barrier.
I'll continue to search IRC, to see if I can dig anything else up.
- This could be a local requirement, so check with your local government.