40mm Waste Pipe Through Stud Wall

hyperbole · Post by **hyperbole** » Tue Mar 29, 2022 10:56 pm

I am planning to build a 2.6m x 2.4m stud wall with 4x2 (89mmx38mm) and would like to run a 40mm (43mm outer diameter) waste pipe through the length of the wall.
The wall is not load bearing but I am planning to board with waterproof tile backer boards and then tile with large 1200x600mm tiles on both sides of the wall (bathroom on one side, ensuite on the other). Wall hung basin and a mirror cabinet will go on one side of the wall.
Studs will be positioned at 400mm centres and I will need to drill through all studs to run the pipe.

(89mm - 43mm) / 2 = 23mm left on each side of the hole (48% removed).

Would this be acceptable or will the strength of the wall be too compromised for what I want to use it for?

I have seen some suggestions of boarding with OSB to add more strength? Happy to do it but will it help and is it necessary? Is 9mm OSB enough?

Many thanks.

fin · Post by **fin** » Tue Mar 29, 2022 10:59 pm

as in running the pipe through the studs so basically drilling upto a 50mm hole through each stud?

arco_iris · Post by **arco_iris** » Wed Mar 30, 2022 5:38 am

Have you considered that (a) 43mm pipe through 43mm hole will be a very tight fit (b) each hole will need to be at a slight angle as the pipe will have a fall on it (c) each hole will need to be a tad lower than the one before. For these reasons, the holes will need to be 50mm to provide tolerance.

And so your studs become even more compromised, to 20mm each side.

So, erect the studs, use a straight edge to mark out the fall/pipe run, notch out the studs from one side only to 44mm (don't bother with holesaw), leaving 45mm at the back, lay in the waste pipe, then OSB or ply the face to provide some strength to support the tiling. Use plenty of screws but DO NOT SCREW THROUGH WHERE THE PIPE RUNS!

18mm board would be better than 9mm IMHO.

Why 40mm waste pipe? Basins only needs 32mm waste, the shower waste will be under the floor.

hyperbole · Post by **hyperbole** » Wed Mar 30, 2022 7:24 am

Thanks for your reply, makes sense. I thought drilling holes retains more strength Vs notching.

Can I use some steel plates if I notch or is OSB still a better option?

40mm because it will be a ~2.5m run. Apparently regs say 32mm can only be run 1.7m max.

fin · Post by **fin** » Wed Mar 30, 2022 7:26 am

having read it again ha.... id be going maybe 5x2 to be honest and notching one side. drilling holes through would be a reet nightmare and trying to get the pipe in and lined up would be a task and a half. also as above 32mm pipe would be the way to go

fin · Post by **fin** » Wed Mar 30, 2022 7:27 am

its the waste fittings that connect to the sink though unless ya wanna fit reducers at the sink end

dewaltdisney · Post by **dewaltdisney** » Wed Mar 30, 2022 7:49 am

I never like buried and hidden pipes, you know you will have to rip holes to get to any leak issues and sod's law dictates you will haveto at at some point. Do not have joints inside the wall if you go this way, just a complete pipe run.

DWD

arco_iris · Post by **arco_iris** » Wed Mar 30, 2022 8:42 am

Hidden pipe runs need not be a problem, DWD, as there will be no leaks when properly installed, solvent weld.

Point taken regarding maximum run of 32mm waste, though I *think* you can go longer if an air admittance valve, or a separate breather pipe are installed? And the total length of run is from the basin to the soil stack, not just the length inside the room. It's surely to do with siphonage (volume/weight of water in the pipe) rather than flow?

OP's 4x2 at 89mm x 38mm is CLS, 4x2 (nominal) sawn would give 95mm - Fin's 5x2 (120mm) may be better.

Yes, by all means affix a metal plate, this will protect against putting a screw through the pipe accidentally, but may need letting in so as not to bow the surface boarding.

hyperbole · Post by **hyperbole** » Wed Mar 30, 2022 9:25 am

Will just be a straight pipe run with no joints, solvent weld reducer at the basin.

I think I will go with 5x2 (125x47) and will add some steel plates.

Thanks everyone.