I am building a bathroom in my basement. It's not a remodel, it's a fully new room from the concrete floor up to the joists.

The partition walls will not be touching the cinderblock foundation; there will be a 4" gap between the non-load-bearing walls of this room and the house's foundation. I am using PT wood for the sole plates.

My question is: Do I need to put a sill plate gasket underneath the PT wood that serves as sole plates for these non-load-bearing walls?

(I am seeing a lot about sill plate gaskets on Google, but the use for this gasket product seems to be more directed towards what goes on top of cinderblocks that are a part of foundations.)

  • It's not normally used for interior walls. If you're bolstering your plate anchoring with construction adhesive you simply can't.
    – isherwood
    Mar 3, 2021 at 14:53

2 Answers 2


Sill plate gasket material is cheap. I would put it in anyway, just to head off having to go back and redo stuff based on what the inspector says.

It's best to keep on the good side of your local inspectors. They can nit-pick you to death, so it's best not to go to war over something as easy to install as the sill plate gasket.

A Bit More Explanation

Here's where I'm coming from. I converted part of a former garage, now a workshop, into a laundry & powder room. The workshop had been fully insulated during a previous renovation but (and this is key) it was never heated or air conditioned, and it still has the original concrete floor. Therefore, by our local standards it is considered unconditioned space. From an insulation standpoint, the partitioned off laundry/powder room is just like being exposed to the outside. Hence the reason I needed to install the sill plate gasket.

  • I disagree with arbitrarily doing things like this without reason. It's wasteful, environmentally irresponsible, and costly.
    – isherwood
    Mar 3, 2021 at 14:52
  • I'm going for it. It's only $6, and I'll donate the leftover material to the hardware thrift store.
    – Mark
    Mar 3, 2021 at 20:57
  • @isherwood Using a sill plate gasket is great for sound control too...especially around their bathroom.
    – Lee Sam
    Mar 3, 2021 at 20:58
  • Fair enough, but I can't say I've ever detected sound coming through under a wall plate.
    – isherwood
    Mar 3, 2021 at 21:20

The primary function of the sill plate gasket is to keep undesirable stuff out, bugs, dust/dirt, outside air, etc., while at the same time keeping desirable stuff in, such as heated or cooled air.

While it can, and often is, used on interior walls in slab construction, it's generally optional there unless your local building codes require it. You may want to check your local AHJ.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.