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?
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
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...
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.
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.
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
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...
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?
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.
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.
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