What you're wanting to do is called slip-lining. It's a common practice
here in Houston and to be perfectly honest with you - on large piping
projects (municipalities mostly) is extremely cost effective. However, the
piping that is used is a very stiff walled polyethylene - is "hammered" down
the line with sophisticated equipment, and prior to all that, the existing
line is televised using GPS equipment so the damaged sections are excavated
and replaced. I don't know how long or deep your sewer line is, but on a
residence, I would replace the entire line. If nothing else, when removing
the old 6" line using a backhoe, the roots will be disturbed and cleared
away from the new line. In over 30 years of plumbing, I've never seen a
*properly* installed PVC line take on roots.

As far as the size is concerned, you would have to calculate the fixture
units to see if you can reduce to 4". Here in Houston, there are very few
homes (even those with 4 bathrooms, 2 kitchens, wet bars, etc.) that would
require a 6" line. I once had a customer who wanted an 8" sewer line
(typical 2 bath, kitchen, w/d, etc.) I told them I would not install it
because it would more than likely stop up over a 4" line. They thought I
was crazy until I explained to them that with that much "barrel size" of the
pipe, there was a good chance that the liquid would run around the solids
and leave them behind in the pipe. Once they thought about it, it made
sense. Good luck to you.

Jim Mc Namara




"jeff" wrote in message
...
Due to tree root problems, I've gotten a few estimates for sewer line
replacement from my house to the curb.

I have two questions. 1) if it turns out that my existing sewer line is
6"
clay pipe, is there anything wrong with the contractor inserting 4" PVC
pipe
through existing clay pipe for some of the installation rather than
removing
the existing clay pipe? The reason for doing this would be to avoid
having
to tunnel under a staircase that ascends in a direction perpendicular to
the pipe and which is located above the pipe. By inserting PVC pipe
through
existing clay pipe, this could avoid damaging the staircase or causing it
to
settle. Is there anything wrong with inserting the 4" PVC pipe through
existing 6" clay pipe in a problem section rather than removing the clay
pipe altogether? None of the clay pipe would be used, since the PVC
pipe
would simply be inserted through it to avoid a problem area. Is this
acceptable?

2) if the existing sewer line is made of metal (cast iron?) and there are
no
joints in it between the house and the location where it extends beyond
the
staircase (11 feet from the house), would there be any problem with the
contractor attaching a PVC pipe to this location (11 feet beyond the
house)
rather than starting at the house itself. The contractor seemed confident
that if the existing pipe is made of metal (cast iron?) and is good shape,
and has no joints, that he could simply attach a PVC pipe to it with a
solid
connection (I think he said a 4 band stainless steel) and seemed confident
there would be no chance of root intrusion at that connection. Is it true
that with the proper connection of a PVC pipe to a metal pipe that there
is
no risk of root intrusion, or should I insist that the PVC pipe's
connection
should begin at the house (and take the risk of potential damage to the
steps by having them tunnel under them.) I think the contractor may have
talked about using a 4 band stainless steel connector rather than a rubber
connector. As much as I'd like to save the steps, avoiding root
intrusion
is more important than saving the steps. Should I insist that the PVC pipe
begin at the house or would connecting to the existing pipe be as solid in
terms avoiding any potential root intrusion?

Thanks.

Jeff