1:40 drainage fall for W.C's

[Vijay]

I'm just digging for the drainage and I think I can just about get away with a 1:40 fall everywhere. While reading something about drainage, it says that any drainage that has W.C's attached should be a 1:80 fall. Is that strictly true?

 

Cheers

 

Vijay

[Onoff]

A bit here on the old forum:

 

http://www.ebuild.co.uk/topic/3629-fall-of-sewage-pipe/

[Vijay]

Thank you. Looks like 1:40 will be fine for 100mm pipe

[PeterW]

I'd go 1:80 unless you really need the drop with 1:40. 

[Vijay]

I've just about got 1:40 (with a bit of work), so I'd really struggle to get 1:80 without core drilling a hole through foundations................

[RichS]

10 hours ago, Vijay said:

I've just about got 1:40 (with a bit of work), so I'd really struggle to get 1:80 without core drilling a hole through foundations................

 

Vijay, I think you've got this the wrong way round.

If you've got 1:40 then 1:80 is already available, i.e. a lot less fall.

If you overdo the fall then the liquids disappear too quickly and leave the solids sat in the pipe, that's why @PeterW suggests 1:80

Edited August 16, 2017 by RichS

[ProDave]

I thought the issue with 1:80 was it is the absolute minimum allowed, so you have to be really careful that nothing happens to allow a bit of pipe to sag. Some say when doing 1:80 under the ground you should concrete it in for that reason.  If you have enough room I would go as close to 1:40 as you can. It's not one or the other, it's anywhere in between.

[CC45]

BC was happy for me to use 1:80 but only with 150mm pipe & concrete.  I stuck to 1:40.

[PeterW]

1:80 shouldn't sag if it's packed properly and bedded - it does if you don't support it in situations such as internal soil pipes. Polypropylene pipe sags worse than uPVC as it has a slightly lower melting temperature. 

[Nickfromwales]

19 minutes ago, PeterW said:

1:80 shouldn't sag if it's packed properly and bedded - it does if you don't support it in situations such as internal soil pipes. Polypropylene pipe sags worse than uPVC as it has a slightly lower melting temperature. 

A bit close to the wind though, and allows little for error? 

[Vijay]

On 16/08/2017 at 08:15, RichS said:

 

Vijay, I think you've got this the wrong way round.

If you've got 1:40 then 1:80 is already available, i.e. a lot less fall.

If you overdo the fall then the liquids disappear too quickly and leave the solids sat in the pipe, that's why @PeterW suggests 1:80

 

 

Not if the foundations and manholes fitted by the developer are are already in place - I would need to drop the foundation or raise the manhole

Edited August 17, 2017 by Vijay

[Vijay]

How should any pipework running under the B&B floor (and on top of the cleared ground) be supported? Do I just use a concrete slab under the rest bends or do I bed any pipework and restbend in concrete?

[Nickfromwales]

If the ground is not great, use a flagstone as a pad, then wet concrete pads on those to actually hold the pipe. Come 1/2 way up the pipe, no need for more than they afaik. Just make sure it's benched either side so it can't move. 

Get a laser and work out the fall over the distance. That'll tell you your fall. 

[Vijay]

Cheers Nick. How often should a pipe run be supported to stop sag?

Edited August 17, 2017 by Vijay

[Nickfromwales]

Id say every 900mm, but there should be a regs standard for horizontal soil pipe runs. 

[Nickfromwales]

Random grab here

[Oz07]

Isn't the whole point of b&b that the ground inside can move and heave? I've never been a fan of long runs underneath beams for this reason. I think it would be preferable to dig a trench filled with pea gravel allowing a big of movement without upsetting the falls. 

[Vijay]

2 hours ago, Oz07 said:

Isn't the whole point of b&b that the ground inside can move and heave? I've never been a fan of long runs underneath beams for this reason. I think it would be preferable to dig a trench filled with pea gravel allowing a big of movement without upsetting the falls. 

 

Can't do that as the foundations are in and the pipes are to be ontop

[TerryE]

On 16/08/2017 at 08:29, ProDave said:

I thought the issue with 1:80 was it is the absolute minimum allowed, so you have to be really careful that nothing happens to allow a bit of pipe to sag.

 

Shit sticks.