Shower Waste Fall

[marshr02]

Looking for advice - probably thinking about it too much. Have 1.8m of 50mm pipe from internal stack running at 20mm/m alongside joists - then swept bend to bring it through floor alongside shower tray. Then there is a 50mm swept T for rodding if required solvent welded as tight as possible to the swept bend coming from below. A 50-40mm reducer in the 50mm T gives the 40mm connection running just shy of 1m @ 25mm/m to the shower tray. The step up from finished floor to tray top is 140mm. Obviously according to paper (18-90mm/m) this is all tickety boo - but I have the option of shoving 18mm ply under shower tray to raise the whole lot 18mm to give a better slope on the 50mm pipe - would this be sensible OR is the current arrangement ok? Seems to me that 18mm/m is an absolute limit which means on site 25mm/m is a more realistic bottom slope to aim for to cope with any floor movement or inaccuracies at 1st fix?

 

[Howsie]

Sounds fine to me. What sort of trap are you using?

 

[marshr02]

From Bathstore - called Fast Flow Shower Waste. Quite a large diameter, say 110mm - from measurement I would say a 50mm trap. What does my head in is if I put a pipe at 20mm/m - then it only has to drop a few mm before there may be problems.

 

[Howsie]

Go with whatever you are comfortable with then. It's OK in my mind but you have to please yourself.

 

[marshr02]

Thanks for reply. Just curious - if I changed the 50mm swept Tee for a 50mm knuckle bend I would gain about 15mm of vertical play which makes everything fine. Everything is a compromise, lose the swept bit (but it is 50mm knuckle bend) and lose the rodding point (which would have been within studwork anyhow), but gain a decent fall. What would you choose? cheers

 

[Jimbob]

I'd rather have the decent fall over the rodding point. If you have the correct fall, it should be self cleaning.

 

[Howsie]

Lose the rodding point as it's inaccessible anyway. My preference would be a greater fall with the knuckle 90. As it's only serving a shower, you'll be fine with 50mm

 

[marshr02]

Thanks guys - those last two points are solid gold. Out of interest what are the regs on rodding points for waste pipes within joist/studwork. I guess often a waste pipe has a bend within these areas - and surely you're not supposed to offer rodding point at every change of direction?

 

[Jimbob]

Thanks guys - those last two points are solid gold. Out of interest what are the regs on rodding points for waste pipes within joist/studwork. I guess often a waste pipe has a bend within these areas - and surely you're not supposed to offer rodding point at every change of direction?

Building regs part H says 'rodding points should be provided to give access to any lengths of discharge pipes which cannot be reached by removing traps or appliances with integral traps'. But in practice you would only do it where practical. You're never going to have problems with a shower on 50mm with the correct fall.

 

[marshr02]

Thanks Jimbob, and Howsie....

 

[PlumberTiler]

what was the outcome because iam going through the same thing myself with a shallow fall on a shower waste

 

[Howsie]

what was the outcome because iam going through the same thing myself with a shallow fall on a shower waste

It's all there in the thread fella.

 

[marshr02]

what was the outcome because iam going through the same thing myself with a shallow fall on a shower waste

So - I've run the pipes. And for the moment I have a temp. bath in the opposite corner and I ran the 40mm waste pipe from this into the shower outlet (no tray yet). The falls are exactly 25mm/m for the 50mm pipe, and 25mm/m for the 40mm pipe (see thread). I opted in the end for a swept Tee (not knuckle) as I managed to make this accessible. After lots of messing around I found the drainage was significantly better if I could raise the shower outlet just 10mm to make 35mm/m. So I'm going to raise the tray 10mm higher. Even so the 25mm/m drained okay. (As you would expect the outlet couldn't handle a whole bath being discharged into it - water everywhere - but it could handle an empty bath with the taps full on) cheers for all advice

 

[Howsie]

THanks for the update.

What outlet couldn't handle a bath being emptied?