Supporting Cast Iron DWV Pipe

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Hello,
I'm planning to do a 25' run of 2" cast iron pipe between floor joists and am thinking about how to properly support it. There are pipe hangers that I could use to support it from above, so I would have to attach these to the subfloor. I was wondering if instead there is a type of support I could use that would attach to the joists on either side. Something like the expandable bar support on a fan-rated ceiling electrical box. Any suggestions or pointers?
Thanks, Wayne
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Wayne Whitney wrote:

Just plumbers' tape (the perforated metal strapping) would work fine as long as use adequate fasteners.
But, one has to ask why, in this day and age one would use cast iron?
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Or even 2 1/2" or 3" conduit C clamps and clamp them to the side of one joist
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That would work except I need to traverse from one side of the joist cavity to the other side over the course of this 25' root. So I could do that at the ends, but I still need a solution for the middle two supports.
Thanks, Wayne
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Yeah, I thought of plumber's tape, but I was looking for something more rigid. An expandable bar would work great.

Cast iron is quieter and I may wish to finish my basement.
Wayne
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Wayne Whitney wrote:

Well you could either rig up something or use the expanding light mounts or similar and I suspect (although I've not searched extensively) there's something very similar for plumbing supports as well available.
But, the plumbers tape will probably just as simple and since it is flexible will undoubtedly be be more quiet. Rigid w/o a a cushion somewhere --> vibration/noise.

I'd go for the PVC for DWV and insulate around it w/ solid foam or similar for the sound retardation, meself...
--
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The noise concern is from flowing waste water through the pipe, I don't think there's going to be much vibration from that. But flexibility still seems like a good idea, so maybe I should just use the plumber's tape. I guess if it seems too flimsy I can always support it more often. Thanks.
Cheers, Wayne
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Wayne Whitney wrote:

I ken, but there's also the thermal expansion/contraction which while not _as_ significant w/ cast as plastic is a potential if the mount is rigid against the hanger. Different noise, surely.
See my other posting on possible hangers if you really decide to go that route, but my guess would be if you get it in place w/ the tape it will be every bit as stout as you could wish, particularly if you on occasion wrap it 360 around rather than just support it from underneath.
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Another good point. I'll go with the plumber's tape. Thanks for the help.
Yours, Wayne
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Wayne Whitney wrote:

No problem...as you may have guessed, I've done very similar before... :)
One more note on the solidity of the mounting since that seems to be your concern--I earlier wrote
"... get it in place w/ the tape it will be every bit as stout as you could wish, particularly if you on occasion wrap it 360 around rather than just support it from underneath."
I'll note that since you have access to the joists, one way to accomplish this is to occasionally where you wrap the tape around to fasten one end solidly, then use a lag or even a bolt through the other end and use that to tension the tape--it'll make a solid mount that still has a little flex. Even though the tape is tightly wound against the pipe, that it isn't rigid means it will move slightly w/ the pipe instead of any inclination of there to be a noise problem w/ a more solid mount.
HTH...
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dpb wrote: ...

OK, since I've gone this far, I'll throw out another option I've used that's simple and effective (albeit not usual for interior plumbing, but what the hey... :) ).
Two wraps of #10 malleable wire (heavy fence wire works, well) fastened solidly to the joists and then just tension w/ a twist. Will work better in this case if the pipe is offset closer to one side so have a little longer span for the twist, but this "trick" is useful for all kinds of problems...
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Wayne Whitney wrote:

Surely not cast iron. Galv steel pipe?
One has to ask, why not PVC?
Have you considered the slope of the pipe? Over a 25' run, the pitch will eat up 6" of the joist depth. Add the pipe O.D. to that......
More details. Exactly what are you attempting?
Jim
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Yes, cast iron.

Cast iron is quieter and this is above a basement that I may wish to finish in the future.

Yes, indeed, it just works. The pipe OD is 2.5" and the fall is 6.25", which makes 8.75". I have old 2x10 joists which are 9.5" deep. So it all fits. I will need to make a larger than usual hole in the subfloor to accomodate the long turn 90 at the upper end.
Mostly I'm just looking for an expandable bar support, I'd prefer that over plumber's tape.
Cheers, Wayne
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Ok, lets suppose you finish the basement. What in the world could possibly happen if some water flowing through a 2" pipe was heard? This seems like such a waste of time and energy.
s
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After living in a house with quiet cast iron drains, drain noise at others houses with plastic drains just seems obnoxious and tacky.
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Oh, please.
s

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If you enjoy hearing every flush go by, more power for you. I'll pass.

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obviously you dont know how noisey PVC pipe is
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Wayne Whitney wrote:

I think they are called riser clamps. A real plumbing store will have them.
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Hmm, riser clamps are designed to rest on the subfloor or bottom plate. So I'd have to nail some blocking onto the side of each joist to give the clamp legs something to rest on. Plus with a horiztonal run, the clamp legs would be flat, so they'd be loaded in their weak direction. Seems like a bit of trouble butdoable, probably sturdier than plumber's tape. This would be a good option if I can find some extendable bar supports.
Thanks, Wayne
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