Remodeling a house in Colorado in expansive soil. Had to remove the slab on grade due to heaving. Will replace with a waffle mat slab. Seems like a great, proven solution to the issue. The foundation is caisson and is in great condition, the issue was the floating slab poured directly on the ground.
Found the lower half of the cast iron badly deteriorated by the damp soil under the slab and it has been removed.
The current pipe is 3" iron.
Permit is pulled and city follows IPC. It appears that the upper end of the pipe is not deep enough under the slab (12" required) to meet updated code. City said they will not require that the existing pipe be brought up to code, but what if it should be replaced with PVC Schedule 40? Upper end was higher than most underlying soil and in dryer soil and did not corrode--looks to be in good shape.
What would you do? Just replace the rotted pipe at the lower end (this part is all 12" under slab) with 3" PVC? This will meet code and should be only the pipe changes that will be inspected I think. Or replace it all with 4" PVC? (appears to only be 3" running to the septic system). Or replace it all with 3" PVC?
Remember soil is expansive so plastic might be susceptible to cracking. Structural engineer recommended Schedule 40. Only have one chance to fix this, will not be removing the slab again.