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This hole in my basement has a roughed-in drain pipe for a bathtub (can't really see it, but I've verified it's there):

enter image description here

As you can see, it's about 12"x16". As I prepare to finish the basement, I'm not really sure how I ought to handle this hole. Should I just run the subfloor up to the edges of the hole and then leave it as-is? or should I do something to seal it once the plumbing is finished to keep critters/moisture/cold from coming out of it?

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Does it need to be accessible? Or are you covering it over? – Chris Cudmore Apr 2 '13 at 13:32
@ChrisCudmore I guess I'm not sure how accessible it needs to be once the plumbing is connected. Anything that can be torn out if necessary without having to remove the tub would probably be ok. – Brad Mace Apr 2 '13 at 15:38
up vote 2 down vote accepted

If you use a tub with an above floor drain, you can finish the floor flush.

If you use a below floor drain, you should at a minimum put down poly, seal the edges with a sealant and cover with several inches of pea gravel.

If you want to insulate a bit, excavate a couple more inches and put down some XPS foam over the poly and then put the gravel over it.

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I'm not clear on where the poly, XPS and gravel are going here. Below the pipe? – Brad Mace Apr 2 '13 at 15:35
You would excavate enough to be at the desired final depth for making the plumbing connections. You could certainly overtrowel with mortar instead of gravel. Poly 1st, xps over, gravel or cement on top – HerrBag Apr 2 '13 at 15:38
The pipe will poke up and probably terminate in an adapter for joining the tub drain and overflow tailpiece. – HerrBag Apr 2 '13 at 15:42
So excavate to create a "box" that the pipe enters into, line with poly (sealed to what? top of subfloor?), line with XPS, then backfill with gravel? What's the benefit of the gravel? Just to help the "box" hold its shape? – Brad Mace Apr 2 '13 at 15:47
Looks like the hole is already lined with wood, I'd use some polyurethane adhesive to seal and staple the poly while the adhesive cures. The gravel is just ballast for the xps. You could wedge it in with a tight fit and be done. – HerrBag Apr 2 '13 at 15:55

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