pvc v abs v cast iron for dwv

kirkhallNovember 18, 2012

I have a remodel coming up. I've had different opinions from the various plumbers and I'm up for a few more opinions from the GW plumbers. :)

We'll be removing one bathroom upstairs, and replacing it with 2 bathrooms. We will need to install 1 additional stack.

Okay, so, the new bathrooms will be over the kitchen/dining space of the main floor. I originally thought I'd want cast iron (at least for the main, new drop that will go through a corner of the LR), so help with noise dampening.

So, what I've heard so far:

Cast Iron is hard to work with and I'll pay a premium. If I just do all PVC, it will be quieter than ABS and not cost as much.

One said, to use ABS for all the horizontal work, and connect it to a cast iron drop.

One specced just ABS for all.

What say you? If you had a hall bathroom running over your kitchen, what kind of horizontal drainline would you use?

What would you use for the new drop that will be in the corner of the LR?


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We moved into a house that had a PVC stack running through the kitchen. Every shower or flush could be heard. So when we remodeled we insisted on a cast iron stack. I have no problem with PVC or ABS for the vents, but not for a any horizontal plumbing or stack that runs through living space.

    Bookmark   November 18, 2012 at 10:32PM
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When discussing pipe, what does the term "Schedule" mean? When most ppl hear the term schedule they think in terms of a time table of events, such as a work schedule or buss schedule, but in truth, the term schedule actually means "a table or list". Now going back to the later part of the 18th century when they first began making iron pipe they made tables of size & wall thickness specifications which are referred to as a "pipe schedule". Basically, for any given size, the higher the schedule number the thicker the pipe wall and the higher the working pressure rating of the pipe.

In the late 50's when they first began extruding plastic pipe they used the same listed wall specs as the iron pipe schedules.

PVC pipe - is actually made in schedules 10, 20, 40, 80, 120 & sometimes for special purposes 30 & 200 however, only schedule 40 is approved for DWV (drain, waste & vent).

ABS Pipe- With some extremely rare exceptions, ABS is only used for DWV and it is only made in sched. 40.

The national model codes approve both ABS & PVC, however some state or local codes will accept one to the exclusion of the other. Generally they will demand ABS so the installers are not tempted to sub the cheaper PVC sched. 10 or 20 in place of the required shedule 40. That is also why when running PVC it must be hung is such a manner that the writing on the pipe wall is clearly visible to the inspector. If he or she cannot see the writing to confirm sched 40 they may red tag your job and tell you the pipe is not hung correctly.

Cost wise ABS & PVC are generally about the same with some price advantage going to the material that is most commonly used in your area because the suppliers get a better frieght rate for buying in bulk.

When deciding which plastic pipe to use we primarily use two criteria.
1. Which material is code approved in your location
2. Which pipe is currently used for the existing DWV system? (code does not permit co-mingling the two materials. It does allow one transition from one type of plastic to the other, but than all new work must be done with the pipe you transition to)

When making a PVC joint you must first apply a cleaner then the glue, whereas the cleaner is not required on ABS. Otherwise the handling characteristics are the same and all that hype their giving you about additional labor is baloney.

Both ABS & PVC can be easily cut with a hacksaw, wood saw and if your in a really tigth spot where you can't maneuver a saw, it can actually be cut with a nylon string.

For sound deadening quality the advantage definitely goes to CI (cast iron) but when compared to ABS or PVC, CI pipe is expensive and very labor intensive to install. CI pipe must be cut with a CI snap cutter or a special cutoff saw and the sections are joined with "no-hub connectors. The no-hub connectors are a neoprene sleeve that is covered with a metal jacket and they have two clamp bands, one on each end of the coupling, which must be tightened to a specified torque setting. We use a special tee handled automatic torque wrench that slips when it reaches the correct torque setting. Cast iron pipe is much heavier than the plastic pipes and it requires much more attention to detail when installing pipe hangers.

For residential application CI pipe is used to construct the 3" or 4" stack and the 3" branch to the waterclosets, but the 1-1/2" & 2" lines from sinks, tubs or showers are generally made with PVC or ABS from the fixture to the point where they tie into the 3" branch.

As I stated above, CI will definitely offer the best noise reduction but due to the cost of materials and labor you can expect the CI to cost 4 or 5 times what plastic pipe would be for the same run.

    Bookmark   November 19, 2012 at 7:15AM
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Good reply pup, you are truly the plumbing guru on here.

I have never tried this, but, I heard that one can "deaden" the sound of PVC/ABS by V notching a 2x6, mounting the 2x6 to the framing and placing/mounting the pipe in the V. Does this work?

    Bookmark   November 19, 2012 at 12:37PM
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Thanks lazypup!

So, is there really no difference in terms of PVC v ABS for sound transmission? (I heard PVC was heavier than ABS/expanded less, or something).

The current DWV of the rest of the house is ABS. But, the 2 bathrooms will be plumbed separately--one into the old system (so ABS?) and one into the new stack...

I'm interested in hearing about the vnotching. Also, is insulation any good at reducing noise? Or, is it mostly a factor of separating the piping from the framing with appropriate hangers to reduce noise?

    Bookmark   November 19, 2012 at 3:33PM
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Kirk -

Depending on your install, I have had success sound-proofing by filling the space between the studs with additional 5/8" sheetrock where the noisy stacks are run. 3.5" 2x4 construction, I usually construction glue 14.5" wide x 4' drywall with 4 pieces of sheetrock - works like a charm and is inexpensive.

    Bookmark   November 19, 2012 at 4:57PM
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How did you affix the extra sheet rock sandwiches to the studs?

    Bookmark   November 21, 2012 at 12:00AM
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