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Question DetailsAsked on 2/4/2018

We have a leak behind our bathtub wall, which makes a dripping noise when the sink, toilet or shower runs?

Our upstairs bathtub, which is tub with surround, seems to have a leak. There is a dripping noise when the sink is turned on, or the toilet is flushed, that comes from behind the wall of the bathtub. When the shower is running, water is dripping down the pipes down to the basement floor. Unfortunately, on the other side of the wall is our other bathtub with surround, so without completely tearing out the bathtub (which we are preparing to do), we can't access the pipes. Any suggestions on methods to figure out what the leak is before demolishing our bathtub?

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1 Answer


Whoa - tearing out a surround would be a last choice - you can commonly access this from below, or sometimes in a pinch up through the wall itself by cutting out a piece of bottom plate to access the stud bay where the leak is. Remember, drain pipe leaks (except for vertical stacks) are low in the wall or in the floor, so the leak likely not really up behind the surrounds at all, or at least not very far. May well be exposed under the tub or in the subfloor.

Here is a typical layout for bathroom drain lines:

I would access from below, using a fiber optic camera. It is pretty certain that, since this occurs with flow from several sources, and only when water is being drained, that you have a DWV (drain, waste, vent) branch (nearly horizontal collector line for the bathrooms, probably 3" or maye 4") or stack (ditto but the vertical run between floors) leak. Or possibly, assuming the tub is the most downstream of the fixtures on the line, a leak in the tbu trap (which may be partly filling from water in the line from other uses as well) - which leaks when it fills to capacity. That drain lateral (tying the basin, toilet, and tub/shower together) is pretty much universally run in the subfloor - so exposed from below if you open up underlying ceiling.

A fiber optic scope or camera typically take a 1/2-3/4" hole for it to run through (so easily patched and touched up) and if initially brought in under the tub near the wall will likely showthe leak. Or ifthe leak is in the vertical stack, the hole may need to be in the wall.

Since it is dripping down the pipes to the basement, actually sounds like it is coming from very near to the junction of the lateral branch and the vertical stack - so perhaps going in about 1-2 feet from the top of the wall the stack runs in would be best - enabling you to see pretty much the entire height of the stack in that area. And wall hole patches are generally less noticeable than ones in the ceiling. Of course, if you trace the drip source with a stethoscope ($10-20 at pharmacies) you should get closer before you put in an inspection hole - remember the drip sound will be BELOW the leak.

One to three holes is usually enough to tie down the location of a leak - then of course a working size hoe needs to be put in the drywall to actually do the repair, which might be a replacement of a piece of cracked pipe, releading a joint in a cast iron DWV line, or perhaps putting on a repair clamp wrap-around coupling over a leak if a lot of work to repair it by replacement. (A good metal-shielded coupling will last 20+ years usually in interior use).

There are also epoxy and fiberglass repair wraps for pipe leaks like this - not my favorite but some plumbers and a lot of homeowners and handymen use them.

Some plumbers have fiber optic scopes - or you can rent yourself at Home Depot, tool rental places, some auto parts stores for about $10-20/day for a handheld to-the-eye flexible "scope" or $20-40/day for a "camera" type which has a small color screen which shows the image.

Be sure to dry the wet area out before closing the wall up - a good few hours to half day of strong fan blowing in the inspection hole or vacuum connected to it (do not make hole so small in that case that the vacuum motor "winds up" or significantly changes pitch, indicating it is experiencing too much of a restriction of flow, which can cuase motor overheating) will commonly dry it out. Of course, if the camera shows rot/fungus then you may need to open up more to see the extent of damage and possibly get that repaired by a a Remodeling - Kitchen and Bath contractor.

Answered 2 years ago by LCD

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