riser clamp questions

Hello folks. Great forum here. Lots of good info.

I have a couple questions regarding vertical vent stack riser clamping. A plumber is going to cut out about a 5' section of 3" cast iron soil pipe thats weeping and rusting. It will be replaced with another piece of 3" cast iron pipe using no-hub couplings. The section to be cut is below the manifold where my toilet, bath, kitchen tie in. The house was built in 1943. I am not sure if there are any riser clamps already installed. I looked in the attic and don't see one. Can't get to see on the main floor is one is there or not. Anyways, to be on the safe side after this work is done(I'm sure the plumber will brace the pipe prior to cutting) I'd like to install a riser clamp in my attic using the joists. There is no subfloor(deck) where the pipe comes through to the attic, its actually lath with plaster. So my intentions are, the two joists that are on each side of the stack pipe run North and South. I plan on cutting two pieces for 2x6 to span the joists going to the East and West. They will be secured to the joists with screws. On top of the 2x6 span I will secure a piece of 4x4 on each of them and the riser clamp will be facing North and South and resting on the 2x6's with 4x4 pieces on them. I am doing it this was because the way the vent pipe comes through the joists, its only about 3 inches from the joist on the East and perhaps 12 inches from the joist on the West.

So here are my several questions:

1) Any problem with using this method?
2) How tight do you tighten the bolts on the riser clamp?
3) In looking at risers on the internet(I'm gonna order one) do I need a
3" riser clamp? The data for the clamp says its for NOMINAL SIZE so is the
3" the one I need? Or do I need a 3.5" Riser?

Thanks for taking the time to read my message.

Your method sounds fine - I did just the same thing in my attic two months ago so I could cut out a section of bad pipe below it.

I would look in your yellow pages and see if there is a plumbing supply house locally that may sell you the clamps. That way you can get the right size, and if you need to return a wrong size it won't be a problem.

Start both the bolts together and alternate until you can't get them tight anymore. It takes a bit of effort but isn't tough. Make sure that if there is a notch on the clamp 'ear' that you face that DOWN so the clamp can't fall!

Thank you very much MG! I certainly appreciate your input.

Along the lines of this thread...

Are rise clamps needed for PVC? I've assume they are, but I do not see a specific requirement and the box stores do not carry the clamps.


Thanks,
Steve

riser clamp

The piping going to the attic has at least one, and maybe more, connections into it for vents or other purposes. They will support the pipe better than any riser clamps you install. I have cut a lot of vertical stacks and have never had to use riser clamps to support the upper section. Even the toilet connection usually has a support board under it.