Plumbing through Floor Joists

utterlydiy · 15 Nov 2020

Want to change the shower and tray.

Current the tray is raised some 120mm enough to allow a shallow bend/trap and 40mm drain pipe acoss above the floor to the waste stack in the corner some 150cm between them. The pipe is boxed along the wall

Would like to have shallow 45mm tray or level access (wet room style) in place of above set-up.

Problem: The current 40mm drain pipe goes across the floor because the floor 6 x 2 joists at 40cm ctrs run right-angle to the pipe.

Can the Joists be drilled safely to allow a 40mm or smaller drain pipe, which may need 4 joists to be drilled. The pipe could run within approx. 10cm to 30cm along the wall between the trap and stack.

CBW · 15 Nov 2020

https://www.labc.co.uk/news/how-get-it-right-notches-holes-solid-timber-joists

Ive done quite a few, notched, not had any issues I’m aware of

Deleted member 174758 · 16 Nov 2020

I've repaired or replaced more than my share of joists over the years where too big a notch had been chopped out or multiple over size notches had been chopped out at different places along the joist. Don"t exceed the recommended maxima

chris911sc · 16 Nov 2020

OP,
I did exactly that recently. 40mm pipe work was above joists(6"x2") /boards and now is under. The notches are between 40mm and 60mm, allowing for slope.
For piece of mind, i added few 4"* 2" with coach screws. Not sure i was necessary, but i sleep better knowing it's done

HERTS P&D · 16 Nov 2020

60mm out of 150mm joist?????

Andy

tony1851 · 16 Nov 2020

I agree that at first glance that seems disasterous; and if it was anywhere near the centre of the span it would effectively become a 90mm deep joist and could possibly fail - depending on the span and particularly in a bathroom.

But the conventional rules about where along the joist and how much we notch/bore are very conservative - deliberately so to allow for over-enthusiastic plumbers and sparks (though it's the plumbers who are usually the worst culprits!).

But if the joist(s) has been cut fairly near the end, it's not nearly as much of a problem. The only issue near the end of the span is the shearing stress on the timber where it goes into the wall. There is a simple equation for checking this, and in many cases it can be shown that the joist will still be OK. It's also not as bad if the notch is out of the top of the beam rather than out of the underside.

Having said that, it's not me sitting in a bath with 160kg of water!

Deleted member 174758 · 16 Nov 2020

HERTS P&D said:
60mm out of 150mm joist?????

Yes... The (conservative) rule of thumb we use is no more than 1/3 of the depth

utterlydiy · 16 Nov 2020

Thanks for the replies.

The joists are 2.5mts long, no bath fitted or no any other load in the area across the joists to be drilled apart from the pan and handbasin.

chris911sc · 17 Nov 2020

chris911sc said:
OP,
I did exactly that recently. 40mm pipe work was above joists(6"x2") /boards and now is under. The notches are between 40mm and 60mm, allowing for slope.
For piece of mind, i added few 4"* 2" with coach screws. Not sure i was necessary, but i sleep better knowing it's done

so my post don't send the wrong advice.....
I re-measured the joists. 2 joists are coupled. They are 169mm. The notch is sloped from 56mm to 50ms into the first joist, and 50mm to 44mm into the second. This is to allow for 40mm shower waste pipe.

diynot

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Plumbing through Floor Joists

Deleted member 174758

Deleted member 174758

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