Q. Do you need to use pressure-treated lumber for the bottom plates on interior partitions over a slab?

A. You won’t need pressure-treated plates on interior partitions for crawlspace and basement houses, but you will need them over slabs. Code requires pressure-treated lumber wherever framing is in contact with foundation concrete. Another very good reason to have pressure-treated lumber plates is to deter termites. Termites can enter through a crack as small as 1/64 inch, and the pressure-treated plate can discourage their entry.