How to Seal a Tub Drain Hole Under a House

Hole cut in plywood subfloor for bathtub drain.

Holes cut in the floor under a house for bathtub drain pipes and other plumbing can allow cold air and rodents—such as mice, rats, and squirrels—into your home.

To seal up holes under your house:

  1. Cut metal flashing larger than the hole so it fits around pipes.
  2. Apply caulking or construction adhesive around the hole.
  3. Screw the flashing to the bottom of the subfloor using screws that are short enough not to penetrate through the floor above.

Watch this video to find out more.

Further Information

Danny Lipford: Uh-oh, look at all that. Look at that big hole there.

Allen Lyle: Let’s see if there’s anything up in there.

Danny Lipford: I hope there’s not.

Allen Lyle: You know, critters get up in here, too. This is a perfect spot during the winter.

Danny Lipford: Well, I tell you, it’s a shame, though, that they leave just these big cuts like that…

Allen Lyle: Well, they did it every time, too.

Danny Lipford: …Without sealing it up. The only way to do it is to put something over it.

Allen Lyle: I got some roll flashing.

Danny Lipford: Oh, perfect.

Allen Lyle: You can cut a piece.

Danny Lipford: Hey, I’m coming back with it.

Allen Lyle: Right.

Danny Lipford: T hat ought to be just about right. Wow, what kind of shears are these?

Allen Lyle: Thunder shears.

Danny Lipford: Is this what they use to cut your hair?

Allen Lyle: You realize if we put that up then we start hearing a knock on the other side…

Danny Lipford: Yeah, we got a problem there.

Allen Lyle: We got a problem there, “Hey, let me out.”

Danny Lipford: Yeah, and see that bottom. The horizontal piece is down below it. So I got to slot it for that, for that whole thing, don’t I? All right, let’s see how close I am on this. Tell you what, I’m going to lay on the ground. Do you have any kind of pillow? Yeah, there it is right there. Yeah, I’m going to need more.

Allen Lyle: Yeah, little bit. Watch your head.

Danny Lipford: Don’t drip any of that on me! Got a feeling I’m going to need a Band-Aid here in a minute.

Allen Lyle: All right.

Danny Lipford: All right, all right. Okay, you want to hold it while I push it in place?

Allen Lyle: Yep.

Danny Lipford: Okay, here we go. Oh, yeah, look at that.

Allen Lyle: There it is.

Danny Lipford: All right.

Allen Lyle: What gets me though is, now that didn’t take us, I mean, what, 10 minutes tops.

Danny Lipford: Right.

Allen Lyle: Little bit of effort.

Danny Lipford: And probably five dollars worth of material.

Allen Lyle: Yeah.

Danny Lipford: All right, bring on the cold weather.


  1. Hello! I was watching the video How to Seal a Tub Drain Hole Under a House and was wondering if you had any suggestions abut a slab foundation with a similar issue. There is a 7×10 inch cut in my foundation and around the drain pipe is gravel. The area is exposed rather than sealed causing a damp/mildew/cave-like smell in my bathroom. Is it normal for a builder to not cover this area? I am not sure what to do as I would have to cut into the drywall in my closet to get to the shower, which has the same issue. It smells like an old musty basement and my home is only 9 years old. I emailed the builder about the issue and of course they said that is normal and will not fix it. Thank you for your insight and suggestions.


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