Waste pipe through structural element

[DIYalot]

Hi. In the two pictures I attach, I show (red circles) where I was intending to pass a shower waste pipe (32mm dia.) through a structural element (large beam) of the house. A person told me that I cannot do this, because it's messing with the structural integrity of the house.

The total (vertical) depth of wood you see is 175mm and wood is about 43mm width.

As you see I live in a no fines house, and I'd have to remove some concrete to get the pipe through to the outside, and then re-concrete the waste pipe in.

So, the question is, is it safe to pass that waste pipe through that beam? I would have though it is okay, but I want some knowledgeable advice. Thanks.

 

[tony1851]

It depends on;

1. the span of the beam;
2. the load the beam is carrying (which is directly related to the span of the incoming joists and any partition wall
they may be supporting);
3. the position of the hole vertically on the beam (on the centreline would be best);
4. the distance of the hole from the end of the beam;

So the best we can say is that it might - or might not - be OK..

 

[John D v2.0]

That shower waste pipe you quote is very narrow, a standard waste pipe is about 43mm external diameter which would need a few mm clearance either side.
And also someone did the same in our house (plumber must have thought the joists were just for decoration) and the bounce in the floor was plenty to crack the ceiling below. And it was very noisy!
So don't rely on intuition to tell you if it's OK, but plenty is done that's not OK and it doesn't usual collapse without warning.

 

[oldbutnotdead]

Given that yon timber is against a wall, if you stick a couple of frame anchors into the concrete (through the timber) that should compensate for the loss of strength resulting from an oversize hole through the timber. But you'd be better off not doing it & finding a different route for the pipe

 

[DIYalot]

Here is the details of construction. The beam is really a plank of wood supported along an outside wall by metal supports every 4 feet. There is a strip of wood (45mm x 30mm) affixed to the lower half of the plank and the joists rest upon that strip as you see in the picture. If we focus on the end of the plank and the last joist, you see that there is a cantilever arrangement. The end of the cantilever is 10" (250mmm) from the last metal support. Any hole is to the left of that support, not on it's right.

I think the practical issue might be, what measures could you take to mitigate the effects of putting a 34mm diameter hole in the position shown. Any suggestions. Thanks.

P.S. Joists are in fact cut into the main plank, not just resting on that wood strip.

 

[PaulUszak]

Mitigation could be achieved by locally doubling the thickness of Plank A. Use a lot of gorilla glue to attach another 6x1 timber to the end bay containing the hole. And use it properly by misting the surfaces with water, and clean the surfaces. Use a lot of strong screws to hold it whist the glue sets and they'll act together as a composite. That should be sufficient to compensate for the loss of section. Then put the hole through the reinforced cantilever.

This is probably unnecessary, but will avoid any doubts.

 

[DIYalot]

I'm thinking of taking a different route for the waste pipe. Instead of adhering to current arrangements, that is to lead the shower and upstairs sink pipes out at height whereupon water then goes into a hopper and fall pipe, to run pipes (or a pipe) on the inside of the outside wall, then out to the drain about 1 foot above it. So, I then fill up the hole in the outside wall, in the bathroom, and remove the outside hopper and fall/drain pipe.

P.S. Waste water here does not connect to a stack pipe. Bathroom or shower and sink water feeds into an outside drain.

 

[John D v2.0]

Sounds like an excellent idea rethinking that way, although remember the rules on fall as presumably your pipe is 40mm internal (32mm will only do a hand basin and hardly any fall at all) According to the approved documents you'll need to make the vertical pipe 50mm and fit an aav to the top, otherwise you're at risk of the trap being sucked out. Hope that help!

 

[Hugh Jaleak]

Hoppers are banned as a new installation for wastes, can only be used as a direct replacement for an existing arrangement. I'd upsize to 50mm waste pipe on exit through the wall, and run that to the gulley, as John has suggested above.