Hi all – we’re doing an underpinning job in my basement and we need to rig a temporary waste line so that we can remove the concrete slab that the current cast iron pipe has been set in (100 years old). I attached a pdf with annotated photos. We’re planning to cut in to the stack and run 4” pvc 2’ high on the wall and ~25 across to a vent next to the traps. We would add strap hangers to brace the run and use a Saddle T to connect to the cast iron pipe. I think we need to set the pipe slope 1/8″ per foot, but other than that i’m looking for the “gotchas” for this approach, thanks a bunch in advance!
Replies
Hopefully the cast iron is below the slab, not embedded in the slab.
in general, waste pipe needs to run downhill at a low slope, and sized so that smaller diameter pipes flow into larger diameter pipes, not the other way around.
You also need to make sure all the drains are taken care of. photo seems to show a condensate line into a cleanout lower than you plan to divert the flow.
How long do you expect this temporary installation will be in place?
Might want to look at a sewer pump that would chop up and move the waste in a lower diameter pipe.
The best way would be to dig up the slab, (start where the pipes are), install replacement waste pipes where they will end up, and move on with the project.
What kind of underpinning are you engaged in?
THANKS! the slab was poured after the house was built so it is embedded in the cement. As you noted we can probably skip the temporary line. Ultimately we want the new one at the same level so as you said, that is probably the easier route to take. We will install a sewage pump but only for the basement fixtures. The reasoning is if the pump goes out we've still got the rest of the house functioning. The old cast iron waste line sits right next to a galvanized water services POE, which is being rerouted. We're nervous about chopping the concrete anywhere near the water service until we're ready to relocate it. But I supposed we can replace the cast iron as far as we dare and then go the rest of the way when we're ready to excavate for that last pin and move the water POE at the same time. Good catch on the condensate line, that was also temporary : ) The underpin job lowers the basement floor ~ 9", currently the 10" CMU sits directly on dirt and we're installing 18" deep pins in 3 pours- along with new columns. THANKS a bunch for your response.
The only issue we’re faced with is that the new waste line will be in the way of the underpinning excavation, forming and pouring. so we may be back to a temp line after all.
post script. we do in fact need to rig the temp line it’s the only way to sequence everything that needs to happen.