Location of waste trap?

[Penners]

I'm installing a shower tray in a location with limited head height, so I want to keep the tray as close to the floor as I can. Unfortunately the shower's waste will sit immediately above a floor joist, so I can't just cut a hole in the floorboard to accommodate the trap.

A couple of feet from the where the tray will be located, there is an area of lower floor. I'm therefore thinking about the possibility of running the waste pipe straight out from under the tray (via an elbow immediately under the waste fitting) and down to this lower floor, where there is more room for me to fit a trap.

So effectively I would have 18in to 2ft of waste pipe run before the trap.

Can anyone please tell me whether this would be acceptable under the regs, and whether you can see any drawbacks to the idea?

Many thanks.

 

[Gervase]

The one drawback I can see is cleaning out the trap - they're notorious for accumulating gubbins like hairs, and if the trap isn't directly under the tray's outlet, then it might be difficult to unclog.
Also, Part H.1 of Building Regs states: "If a trap forms part of an appliance then the appliance should be removable. All other traps should be fitted directly after the appliance and should be removable or fitted with a cleaning eye."
The minimum diameter for a trap under a shower is given as 40mm, with 75mm depth of sealing water.

However the legal requirement, as opposed to the recommendation, is merely that "Any system which carries foul water from appliances within the building to a sewer, a cesspit a septic or settlement tank shall be adequate."

 

[Penners]

Thanks for your thoughts, Gervase. Cleaning is a fair point - actually in the "remote" location that I'm considering for the trap, this would be quite easy.

However, the phrase "should be fitted directly under the appliance" is pretty unequivocal (which is more than can be said for "shall be adequate"!). So maybe I'll have to get back to the drawing board.

While I have your brains at my disposal, do you happen to know the minimum head of water that must exist between a mixer shower sprayhead, and the surface of the water in the header tank? I've been googling this for ages, and I just can't find it.

Thanks again
David

 

[rogerh]

However, the phrase "should be fitted directly under the appliance" is pretty unequivocal

It's "fitted directly after the appliance", which is a bit more equivocal.

This one's not much deeper than an elbow:

http://www.plumbworld.co.uk/433-16263

(My first post!)

 

[Gervase]

That suction trap looks ingenious - in fact I'm now going to order two to replace the dodgy traps in our showers (the undersides are currently exposed, so now is the perfect time). Ta for that, Roger.

As for the hydrostatic head, I dunno - save that plumbers do recommend a booster pump if you don't have enough pressure. In plumbing terms, a low-pressure system is one with under 2m head of water.
That said, I've seen them working perfectly well and pumpless in a top floor bathroom with header tank in the attic - maybe a matter of five or six feet above the tap.

 

[Andrew Bodenham]

The manufacturers of your mixer valve should be able to suggest the minimum working head for acceptable performance.
My bristan valve is designed to work on low pressure. From shower head to tank fill level is about 5 foot, and we've been completely satisfied with the flow rate. Ok, you don't get blown away, but it's fine for all normal showering needs. When I installed it I made sure that the pipe runs from tank to hot cylinder to shower were as short as possible, used only pulled bends, full bore isolating valves and 22mm pipe throughout. Hot and cold run from the same tank of course, so equal pressure.
Not having a pump means one less, thing to go wrong, as well as saving water and not having pump noise - an important factor if you have late night / early morning users.

 

[Penners]

It's "fitted directly after the appliance", which is a bit more equivocal.

Yes, you're right thanks, Roger. I misread that.

The vortex waste looks interesting, but are you sure that it's also a trap? There doesn't seem to be any mention of that on the Plumbworld page. As Gervase has mentioned, a 75mm depth of trap is needed for an upstairs shower, so I don't reckon that waste fitting would be acceptable, even if it does incorporate a trapping function. Pity.

I've seen them working perfectly well and pumpless in a top floor bathroom with header tank in the attic - maybe a matter of five or six feet above the tap.

That's useful to know, thanks Gervase. As Andrew has observed, a pump is noisy, and one more thing to go wrong, so I think I'll take a flyer on it without a pump, using a low pressure mixer.

 

[Moo]

Penners - one thing you didn't explain in your otherwise typically lucid description of the problem is the reason why the shower tray cannot be moved a few inches, or turned so that the outlet is between joists.

 

[Penners]

It's all to do with the shape and size of the room, Moo. It's under the angle of the roof, exceedingly small and with features that make the positioning of the shower precise to within millimetres! I'm already having to use the smallest appliances (ie shower tray, loo, basin) that I can find.

It won't be the most comfortable of en suite shower rooms, but it will be particularly useful when we have a houseful of people.

 

[middi]

A washing machine trap is about two feet from the inlet, and they work fine.

 

[Penners]

Good point, Middi. Thanks.

 

[Lime]

The disadvantage of having a trap some distance away from the shower tray is smell.
The pipe prior to the trap will get dirty and the air within it will be flushed out back into the shower room every time it is used.

If there is space for an elbow joint then an inline trap might be more suitable.

I'm not certain about the Typhoon Vortex waste.
It sounds a good idea but Penners does have a point about the 75mm water seal.
It is possible that the trap is made of a series of small water traps (like some under bath traps) so it would amount to a 75mm seal.
Perhaps someone interested buying the trap could ask the website for expert advice.

 

[David Dyer]

There are several shallow shower traps available from Plumbworld, http://www.plumbworld.co.uk/433-0000
We used one in our ensuite for similar reasons as Penners it's worked fine so far (about six months)

 

[Penners]

Thanks for the point about smells, Lime. I hadn't thought of that.

There are several shallow shower traps available from Plumbworld, http://www.plumbworld.co.uk/433-0000
We used one in our ensuite for similar reasons as Penners it's worked fine so far (about six months)

Thanks, David. I have an effective shallow trap on a downstairs shower, but Gervase says the regs require an upstairs trap to have a 75mm depth. I suspect that this is prevent the trap being "pulled" by the vacuum effect of the water descending the downpipe.

Is your upstairs, and has it resisted being pulled?

 

[David Dyer]

Hi David,
it's upstairs and has given no problems at all, from memory there were no warnings on the packaging to suggest that it couldn't be used in certain circumstances.
It was about 90mm deep from seal under tray to the bottom so I guess complies with the 75mm that Gervase mentions.

T'other David

 

[David Dyer]

Hi David,
Oops have just looked at the Marley site http://www.marleyplumbinganddrainage.com/index.cfm?path=diyer.literature&RangeID=11
And it says don't use shallow trap if going to a soil stack so although we don't have a problem it's not recommended.
t'other David.

 

[Penners]

Thanks, David.

 

[Gervase]

The Vortex Cyclone jobbies have arrived. The thing is a trap as well as a simple waste. Rather clever design, with the chamber folded back on itself horizontally. So far I'm impressed, but I haven't fitted either of them yet.

 

[Penners]

The Vortex Cyclone jobbies have arrived

Don't you think you could have phrased that more delicately, given the general subject matter?

 

[Gervase]

Ah, sorry - probably a Freudian slip. I just hope no-one takes the p!ss...