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Question DetailsAsked on 1/6/2015

Cost and feasibility of moving a plumbing vent pipe?

My husband and I bought a 1950s ranch and are hoping to remodel the bathroom. We opened up the dividing wall between the two halves of the bathroom and realized that the plumbing vent pipe is exactly where we would like to remove a wall and put a double vanity. I'm hoping to get an idea on the cost and feasibility of moving the vent pipe about a foot further away, so that we can remove the wall currently covering the vent pipe. It's an old cast iron pipe and leads up to a roof vent on our rolled shingle roof. Given that the roof is just one big shingle, I'm not sure if would even be feasible to move the vent on the top. Would love some advice!

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1 Answer


Depends a lot on how it is plumbed - if it has vent lines from fixtures leading to it in that stretch, you would have to move them to the new location and redo their connections. If this is just a riser vent without connections along the wahy, then no big thing to cut below your wall removal area and move over a foot or few into a different stud bay (or even into another convenient wall) using 45's, and running up through the wall elsewhere. Commonly you can even jog back over in the attic so you don't even have to move the roof penetration, though that is no big thing for a roofer to do either. Oh BTW - unless you live in a Stuart Little or Borrowers sized house, your roof is not one big shingle - the roll roofing typically comes in 3-5 feet wide rolls so there are overlapping seams every few feet up and down the slope anyway, so splicing in a repair patch of sheathing and roofing at the old vent location is not a problem if that is needed - probably about $200-300 range for that part alone if needed.

The plumbing part - probably about same cost range (aspartof overall remodel) assuming pipe is accessible in basement, crawlspace, or torn out wall location, maybe to twice that if harder to get at or there are multiple connections to be made to it. While cast iron is quietier, especially on a vent line which should not have water running in it anyway and is easily insulated around with fiberglass for noise control, I see no reason (unless your area has antique laws prohibiting it) with running PVC or ABS pipe from the vent pipe cut point upwards through the roof, or to another splice back to iron (with appropriate support for the weight) under the roof, as applicable. If going to plastic pipe, I would try to avoid having a stray piece of heavy iron pipe hanging off the top even if it is supported - I would run plastic through the roofjack up into the air, upsizing at the roof as needed to be able to use the same roofjack.

Ballpark costs above do NOT include costs for drywall repair in walls for the new run - but in interior walls it is not uncommon to be able to drill top and bottom wall plates from attic and basement/crawlspace and run the wall portion in one piece without opening up the wall it is running through - assuming no connections are needed in that run.

You will haveto talk to your architect or remodel contractor about feasibility and cost for your specific situation, but with jobs able to avoid roof vent relocation you might well get it for well under $500, on from $500 range on up to maybe $700-1000 range if several intermediate connections are needed and you are required to stay with iron and you also have to relocate roof location too.

Above answer assumed you were talking the main stack vent - this might just be a tub/shower or toilet or basin vent run leading to the main stack vent, in which case it might be far easier to reroute and reconnect with just a few feet of run - either by moving it a few feet over for the run, or even connecting into another vent pipe from another fixture, depending on how plumbed.

Answered 5 years ago by LCD

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