Thread: Trap under Concrete

I saw this recently in Florida. It is under the concrete pour. I was not aware this was allowed due to non access to the trap. Comments?

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Hopefully Jerry will see this and chime in since that's his stomping grounds. He would know the requirements down there.
If I were the owner I'd be pretty worried. The ground doesn't look well prepared or tamped. The pipes obviously just look like they are set in loose dirty. Any movement in the dirt or concrete is going to transfer straight to the pipes.
Plumbers up here bury traps in the ground for new construction as well, not really an issue though. The pipes are cast iron and surrounded with gravel and a vapor barrier.

If the trap is removable or has a cleanout on it, then yes, you would need access to it.

Slab foundations will have the tub/shower trap in the slab, it is about the only way that it can be done. I have a slab foundation and at each bathroom I have a clean-out port in the ground around my home.

I agree with the soil not being prepped very well. Also what about the reinforcing steel and a vapor barrier?

This is typical of slab plumbing installation in my area. Traps are in the poured concrete slabs in the Carolinas.


Andrew Constantine
InspectPro Home Inspections
Charlotte NC Home Inspectors

Where is the vent pipe?

Originally Posted by Rick Cantrell

Where is the vent pipe?

I'm assuming off the wye going to the right and out of the picture to a lav?

Originally Posted by Scott Patterson

Slab foundations will have the tub/shower trap in the slab, it is about the only way that it can be done. I have a slab foundation and at each bathroom I have a clean-out port in the ground around my home.

I agree with the soil not being prepped very well. Also what about the reinforcing steel and a vapor barrier?

Well, yes, but it should be boxed out of the concrete pour at some point. You don't just embed the trap in concrete!

As Scott and others have said, it is acceptable. It is the only way to put a drain under a tub or shower with a slab on ground.

The soil prep has not been done, that looks like it is ready for, or being made ready for, a "underground plumbing" inspection.

After that inspection the trenches are back-filled with clean fill, the soil compacted during the back-filling, then the soil termite pretreatment applied, then plastic sheeting (moisture barrier) is installed over the termite pretreatment, the joints are lapped at least 6" and taped, then the steel and WWM is installed, with the steel on chairs and the WWM on chairs.

Originally Posted by Jerry Peck

As Scott and others have said, it is acceptable. It is the only way to put a drain under a tub or shower with a slab on ground.

The soil prep has not been done, that looks like it is ready for, or being made ready for, a "underground plumbing" inspection.

After that inspection the trenches are back-filled with clean fill, the soil compacted during the back-filling, then the soil termite pretreatment applied, then plastic sheeting (moisture barrier) is installed over the termite pretreatment, the joints are lapped at least 6" and taped, then the steel and WWM is installed, with the steel on chairs and the WWM on chairs.

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Interesting. What I expected to see, from past experience (in NJ), is a "box" in the concrete, similar to a tray in a depressed shower" so that the trap was accessible under the tub.

Jerry, I agree, it appears to be ready for an inspection and prepped for a pour. Strapping the verticals to rebar to insure when the slab is poured they are straight and in their proper place has not been done yet.

Just a side issue, in situations like this with plastic pipes, do they pressure test the pipe in some way to insure there is not a small leak that will allow effluent to saturate the ground over time?

Some of the comments/questions in this thread can be answered by thinking about the work flow.
1. Probably the pad was properly compacted.
2. The plumber digs trenches for the ground work. The loose soil in the photos is from the plumbing excavation.
3. Plumbing inspection done if required and the loose soil compacted back into the trenches.
4. Moisture barrier installed.
5. Rebar and/or tendons installed.
6. In floor electrical installed.
7. Pre pour inspection if required.
8. Pour.

Originally Posted by Rich Goeken

Interesting. What I expected to see, from past experience (in NJ), is a "box" in the concrete, similar to a tray in a depressed shower" so that the trap was accessible under the tub.

The box under the tub does not allow access to the tub trap, which is down in the ground, that only allows the plumber to install the tub drain and overflow without having to chip out concrete - when is the last time (first time?) you could get see the tub trap under the slab?

Originally Posted by Jerry Peck

The box under the tub does not allow access to the tub trap, which is down in the ground, that only allows the plumber to install the tub drain and overflow without having to chip out concrete - when is the last time (first time?) you could get see the tub trap under the slab?

Last time was 8-10 years ago as I don't usually look at that.
In that case there was sufficient space for the trap and drain, access was from the end. Judging from the responses, it is not done now. It was low enough so that the tub could be closer to the floor and not need to allow space for the drain under the tub. Made the tub deeper by a few inches.

Originally Posted by Jerry Peck

The box under the tub does not allow access to the tub trap, which is down in the ground, that only allows the plumber to install the tub drain and overflow without having to chip out concrete - when is the last time (first time?) you could get see the tub trap under the slab?

Last time was 8-10 years ago as I don't usually look at that.
In that case there was sufficient space for the trap and drain (as with a wood floor), access was from the end. Judging from the responses, it is not done now. It was deep enough so that the tub could be closer to the floor and not need to allow space for the drain under the tub. Could install a deeper tub by a few inches.

Originally Posted by Jerry Peck

The box under the tub does not allow access to the tub trap, which is down in the ground, that only allows the plumber to install the tub drain and overflow without having to chip out concrete - when is the last time (first time?) you could get see the tub trap under the slab?

Originally Posted by Rich Goeken

Last time was 8-10 years ago as I don't usually look at that.

Rich,

I suspect that was only visible because someone dug out over and around it to, possibly, replace it. Of course, though, that would destroy the termite pretreatment (if that was done) and that area would need to be re-pretreated.

Down here, that area is filled with concrete after the tub is set.

Originally Posted by Jerry Peck

Rich,

I suspect that was only visible because someone dug out over and around it to, possibly, replace it. Of course, though, that would destroy the termite pretreatment (if that was done) and that area would need to be re-pretreated.

Down here, that area is filled with concrete after the tub is set.

Jerry,

It was a small concrete "pit" in the floor at the drain end of the tub, in about a 385 home small adult community, easily visible when walls were up and nothing else. (I live there, and no... I'm not going to remove the hatch, scrunch down through coats, etc to take a picture).
As for termite treatment.... the company that had the contract, (3 years) didn't even come around once a year with a dog & pony show. But, they wanted a renewal at the end of the 3 years----ya, sure.

Rich

Originally Posted by Rich Goeken

It was a small concrete "pit" in the floor at the drain end of the tub, ...

Now that is a very good way to address those traps ... for tubs ... would not be able to do that for showers, though.

To avoid disturbing the termite pretreatment, the code (at least the Florida code) requires a means of accomplishing similar to what you described, except that the trap is still hidden below ground.

A plastic tub in installed over the riser from the trap inlet, with its top lip set at the level of the top of the slab. When the concrete is placed for the slab, the plumber can access the under-tub area without having to disturb the soil or the termite pretreatment of the soil - the plastic box protects that from happening (unless the plumber goes hog wild and rips the plastic tub out ... ).

As some have said, that's how its done. I know of nothing that requires the trap to be "accessible" from the exterior.

Originally Posted by Joe Funderburk

As some have said, that's how its done. I know of nothing that requires the trap to be "accessible" from the exterior.

... or from the interior ... unless the trap has slip joints in it, then the slip joints are required to be accessible.

Originally Posted by Rich Goeken

I saw this recently in Florida. It is under the concrete pour. I was not aware this was allowed due to non access to the trap. Comments?

What concrete pour? I doesn't look done to me yet. Most homes in Virginia are done this way. They just put a concrete form around it so it stays open and accessible.

Originally Posted by Daniel Rogers

What concrete pour? I doesn't look done to me yet. Most homes in Virginia are done this way. They just put a concrete form around it so it stays open and accessible.

Let's presume that is a shower drain, going in under a concrete slab on ground ... I am having a problem figuring out how that would remain accessible after the concrete slab has been poured, let alone with a shower above it.

If that is for a tub, then after the tub is set, that should be filled in with concrete lest a hole in the slab is left open to allow all that moisture up into the house, and then there is the termite pretreatment which would be disturbed during setting of the tub and would require re-treatment before being filled in with concrete.

Either way, I don't see how that trap would end up being accessible ... unless one considers digging a tunnel in under the slab as an access to the trap??