Hi, we’ve got around to doing the main bathroom in our house renovation but have been scuppered by one plumber that’s visited….

Would just like to sanity check what he’s said. We currently have 14cm of depth under the floor to play with space wise, we have bought a shower with a walk in shower tray and that has an 9cm depth waste attachment so that gives us theoretically 5cm difference for the pipe to slope down from the waste.

Is this acceptable? I read that for every 4 metres of pipe the minimal drop needs to be 1cm down and our waste pipe would be 3.2m long so I’d say even 4cm drop in total for 3.2m would be fine?

Would appreciate any help or advice, as he’s suggested we should raise the floor height to get extra drop, but doing that then brings us too close to the ceiling and being 6ft 1 my head would be literally touching the shower head 🤣

Thank you, Chris

fall for 40mm pipe should be 1:40 which is 18mm/m.

I have a long run of drain that is barely the 1:40 fall and its a pain/ Ok its 10 m long with 3 right angle bends but it needs 2 rodding eyes and rodded every now and then to keep it flowing

You do need 1:40, or it will block with bits of hair, etc. I had a similar problem and managed to source a compact drain fitting that I could swap with the one in the shower tray. The fitting needs a water trap to stop smells and gases from the sewers coming back up, and you need a certain head of water so that the suction from the toilet flush water going down the pipe doesn’t pull the water out of it – this fitting was cleverly designed to do all that in less distance, and you can unscrew the grating on top to clean it out.

Okay thanks, I think we’re going to get another plumber and see what they think.

A
We definitely need as much fall as we can as the missus has ALOT of hair, long long curly hair 😆 it gets everywhere.

One time my toe felt sore, took my sock off and somehow her hair had got into my sock, and wrapped itself around my little toe and cut off all its circulation, luckily I realised and wound it off 😆

You have wind on toes?

Wow

Blazin-saddles
Free Member
fall for 40mm pipe should be 1:40 which is 18mm/m.

I am probably doing this wrong but 1/40 =0.025 Thus 25mm/m, where do you get 18?

Does the 14cm measurement include the thickness of the floorboards?

Don’t put extra on the fall this will tend to leave solids in the pipe.

25mm/m is correct, 18mm/m is the minimum.

Solids in the shower? Wrong on every level!

Can you build up the entire floor to the required level? Depends on whether you want/need flat access into the bathroom?

OP’s missus:

Don’t put extra on the fall this will tend to leave solids in the pipe.

Why’s that, out of interest?

I have a similar calculation to make fairly soon.

Not sure if this will help OP, but ‘Evolution’ do a slimline shower tray with compact waste that might help…

http://www.traymateproducts.com/tmukpdf/TMUK_Brochure.pdf

I agree you need to work to 25mm per M, or 1 inch per M is how I was taught it.
(my old neighbour and plumber told me that regs say 18mm per m, all plumbers work to 25mm in practice)

I have used bath traps in the past where drop was an issue as they are deliberately designed to be very shallow. I guess it will come down to how standard the new shower tray waste hole is and what you else you can get to fit that, as if you are restricted to using that waste with 9cm drop I dont think you have a choice but to raise the shower tray – or redesign your bathroom layout (which may not be possible/practical) to be able to get sufficient fall to avoid issues with the pipe clogging.

I would look around – ask plumber to see if there is a different waste that fits the tray with a very shallow design.

Rereading your post you need min 80mm drop in the waste (pipe centre to pipe centre) so you need either a waste which is no more than 6cm below base of tray at the bottom of the outlet which seems very shallow based on a 40mm pipe, or raise the shower tray / whole floor sufficiently to get the waste to that height.