Proper method to replace portion of drain line underneath block foundation wall?

[lkellogg]

Hi All,

Looking at replacing the cast drainpipe under the basement slab sometime in the next year or so... Are there any special considerations when handling the excavation/replacement of the portion of the drain line that passes under the block foundation wall, and leads outside to the septic tank?

The block foundation sits on top of a concrete footing. Would it be proper to excavate an 18" wide trench underneath the footer/block wall in order to remove/replace the cast drainpipe? Or is some kind of special support needed for the wall/footer?

Maybe I'm overthinking it, but it's the one aspect of the job that seems pretty critical to understand...from a structural standpoint.

Thanks for any insight.

 

[Master Plumber Mark]

Sounds like a lot or digging, jack hammering and hard work to me......
I assume that the cast line is leaking or cracked??

I suggest that the very first thing that you do just before you start this project
is is pump out the septic tank just to be sure of no
back flow .... and do not do this work during the rainy season

If the line is under the foundation then you have some serious digging to do
maybe as much as 4 feet down under the slab in the house.... if their is a cleanout you should
be able to throw a ruler down and hit the bottom to see how deep it actually goes.....

maybe they put a sleeve through the wall to protect the pipe and maybe they did not
way back then....I would pray that they did

If it is just laying on the foundation it will not be as nasty but still a lot of fun....

 

[Sponsor]

 

[lkellogg]

Sounds like a lot or digging, jack hammering and hard work to me......
I assume that the cast line is leaking or cracked??

I suggest that the very first thing that you do just before you start this project
is is pump out the septic tank just to be sure of no
back flow .... and do not do this work during the rainy season

If the line is under the foundation then you have some serious digging to do
maybe as much as 4 feet down under the slab in the house.... if their is a cleanout you should
be able to throw a ruler down and hit the bottom to see how deep it actually goes.....

maybe they put a sleeve through the wall to protect the pipe and maybe they did not
way back then....I would pray that they did

If it is just laying on the foundation it will not be as nasty but still a lot of fun....

Thanks Mark...I had the line located earlier this year due to a suspected leak, and where it passes under the foundation wall and heads towards the septic, it's approximately 2' below the soil level/footer.

I can picture exactly what needs to be done...which is to dig about an 18" wide trench just outside the house, against the foundation wall...and approximately 2.5' deep to access the cast pipe. I just wasn't sure if having an 18" wide section of the footer with no soil/support under it was going to pose structural concerns or not.

All of the buried cast under the interior of the basement slab will be a lot of cutting/hammering/digging...but the transition where it goes from under the slab inside, under the foundation wall and into the soil outside is what has me thinking.

 

[Master Plumber Mark]

You gonna need a bigger and probably wider hole...... on both the inside and outside
because the cast is not gonna come out easily and you will need to get your body down into
the pit to beat on and man handle that section going through the wall... You are probably not
gonna be able to lay on your belly ---head first-- down into a tight hole and fight that pipe....
its just too hard a strain on the body


maybe you will be lucky and they put it in a sleeve
but I highly doubt you are gonna be that lucky...

and also you will probably
have to somehow rheem and chisel on the concrete wall a good bit to
get it large enough to force the new pvc pipe through it....

 

[Sylvan]

NYC1968 plumbing code stated that, unfortunately, a lot of installers did not do this basic requirement

"All piping passing through a foundation wall shall be protected by an Iron pipe sleeve, arch, or lenthal."

 

[lkellogg]

NYC1968 plumbing code stated that, unfortunately, a lot of installers did not do this basic requirement

"All piping passing through a foundation wall shall be protected by an Iron pipe sleeve, arch, or lenthal."

And it's referring specifically to pipe that perforates a foundation wall? Or does that include passing underneath a foundation wall (buried under a footer)?

 

[Master Plumber Mark]

And it's referring specifically to pipe that perforates a foundation wall? Or does that include passing underneath a foundation wall (buried under a footer)?

The protective sleeve is supposed to be for both through and under the foundation....

its really not that hard to throw a piece of 6 inch sch40 pvc through or under a wall

 

[Reach4]

It's possible that putting in a new pipe around the cast iron pipe could work better for you. Have a working path to the septic while you do the hard part of the project. Then switch the flow to the new pipe, and abandon the old section of cast iron in place. Just an idea.

I would use dual-rated PVC (pressure and DWV). It is stronger than the DWV-only foamcore pipe. The price difference for this short run is not that much. Same size. Same fittings.

Is your upstream plumbing cast iron also? If 3 inch plastic, you could make the new path under the foundation be 3-inch PVC.

 

[Sylvan]

And it's referring specifically to pipe that perforates a foundation wall? Or does that include passing underneath a foundation wall (buried under a footer)?

Most codes are ambiguous; the code intent is to protect the piping from bearing any structural weight or coming into contact with cement or anything that may be detrimental to the piping.

 

[Master Plumber Mark]

I doubt you will see 3 inch cast going out of the house to the septic
so odds are its 4 inch cast going out of the house..

that means at least a peice of sch 40 pvc in 5 or 6 inch is gonna be necessary
and someone is gonna have to chisel out that wall large enough to fit that through it
or dig out under the foundation ...

either way its gonna be a lot of fun

you are gonna need a bigger hole.....

 

[lkellogg]

It's possible that putting in a new pipe around the cast iron pipe could work better for you. Have a working path to the septic while you do the hard part of the project. Then switch the flow to the new pipe, and abandon the old section of cast iron in place. Just an idea.

I would use dual-rated PVC (pressure and DWV). It is stronger than the DWV-only foamcore pipe. The price difference for this short run is not that much. Same size. Same fittings.

Is your upstream plumbing cast iron also? If 3 inch plastic, you could make the new path under the foundation be 3-inch PVC.

Thanks, I had considered this, primarily because one of the runs of the current cast iron passes within 1' of a load bearing support post. I'd imagine it probably be fine to cut the floor near it, as long as I keep the trench tight and leave a few inches of concrete on the side of the post closest to the current cast iron's location.