Soil Run Fall

[Onoff]

Got all my bits to mod the soil pipe runs in my loft. It's 1.5m horizontal left to right, goes into the branch/bend then off left 3m where it goes into a bend & the external stack.

 

I've got to make up some timber packs here and there. In terms of minimum fall I've read between 1 in 40 to 1 in 80.

 

Any preference?

 

 

[bassanclan]

You don't want to go above 1:40 as it will be too steeply sloped, or below 1:80 as it won't be steep enough, so aim for 1:60, but be flexible depending on obstacles etc

[Miek]

I've always wondered why too much fall is a problem. Then I found this... 

 

Above ground and below ground horizontal drainage pipes should be laid to an adequate gradient.

 

Gradients from 1 in 40 to 1 in 110 will normally give adequate flow velocities.

 

A gradient of 1 in 80 is suitable for commencing calculations for pipe schemes.

 

If a gradient is too steep i.e. steeper than 1 in 40,  the liquid may run faster than the solids in the sloping foul water pipe thus leaving the solids stranded, which could then block the pipe.

 

If the gradient is not steep enough, i.e. less than 1 in 110, then the pipe could still block if the solids slow down and become stranded.

[Onoff]

Thanks all. Not a job I'm looking forward to, cutting a "live" soil pipe in a hot loft even after the 10 or so bleach laden flushes I'll give the en suite wc! I usually wear a mask smothered in lavender essential oil.

[CC45]

Dont do it when people are at home and using their facilities - a quiet mains soil pipe may help to reduce positive pressure in the system.  Are you going to video it and post up here??

[Nickfromwales]

Take the lid off the manhole whilst your doing it and plug the outlet to the sewer with a couple of bin liners folded into a ball / plug . Leave that off to ensure any stench stays outside. 

Dont do this if anyone's needing to send U571 to a watery grave . 

[Onoff]

5 hours ago, Nickfromwales said:

Take the lid off the manhole whilst your doing it and plug the outlet to the sewer with a couple of bin liners folded into a ball / plug . Leave that off to ensure any stench stays outside. 

Dont do this if anyone's needing to send U571 to a watery grave . 

 

They'll still need the downstairs cloak wc bearing in mind the time I take!

 

Crap photo but that cloak waste comes in from the right and enters the stack below the penetration to the new bathroom. I'll be working at the top of the vertical stack:

 

 

I can also leave the branch access cap off as any "use" will be below.

 

[Nickfromwales]

Cool. Remove the cap, ram the bin liners up the pipe nice and snug and then replace the cap.

[Mr Punter]

11 hours ago, Miek said:

If a gradient is too steep i.e. steeper than 1 in 40,  the liquid may run faster than the solids in the sloping foul water pipe thus leaving the solids stranded, which could then block the pipe.

 

This is no longer considered the case.  There is no evidence that solids get left behind and so there is no maximum gradient.

[Miek]

9 hours ago, Mr Punter said:

 

This is no longer considered the case.  There is no evidence that solids get left behind and so there is no maximum gradient.

When it comes to sign off by the BCO what's the score? Do they check falls? 

 

 

[Jeremy Harris]

39 minutes ago, Miek said:

When it comes to sign off by the BCO what's the score? Do they check falls? 

 

 

 

No, unless you happen to have an "old school" inspector!  The falls should be on a full plans submission anyway, at least indirectly, as the invert levels at key points in the foul drain run are supposed to be shown on the plans.  With these, and the scale on the drawing, the fall can be calculated.

 

What seems to have happened is that the guidance on falls has changed sometime over the past couple of decades, but this hasn't filtered through to those applying the regs very well.  There are still well-respected sources telling people that they need to install a back-drop chamber if the fall is steeper than 1:40, for example, despite the fact that it's been shown to be OK to use steeper gradients.  I'll admit to being caught out by this myself, as back when I first installed a foul drain run the "between 1:40 and 1:80" rule was strictly applied.  I only realised it had changed, in the light of evidence from more recent testing, after someone posted here to point it out.

 

Part H makes no mention of steep falls being a problem now, so if an inspector gets a bit uppity about it, just show them what's in the Approved Document.

[Miek]

Good news, thanks folks

[Nickfromwales]

On some seemingly 'flat' runs the worst I've ever had was simply to 'demo-flush' the run with some loo roll and demonstrate it working. 

[Mr Punter]

27 minutes ago, Nickfromwales said:

On some seemingly 'flat' runs the worst I've ever had was simply to 'demo-flush' the run with some loo roll and demonstrate it working. 

 

With a turd popped in for good measure (and for real world accuracy)?

[Russell griffiths]

I use lumps of banana, bit strange dropping them in the loo and running outside to see what pipe the shoot out of. 

[Nickfromwales]

1 hour ago, Mr Punter said:

 

With a turd popped in for good measure (and for real world accuracy)?

If you can reverse cowgirl a 110mm pipe with that kind of accuracy you should be in a different job   

[Onoff]

On 11/05/2018 at 00:06, Nickfromwales said:

Take the lid off the manhole whilst your doing it and plug the outlet to the sewer with a couple of bin liners folded into a ball / plug . Leave that off to ensure any stench stays outside. 

Dont do this if anyone's needing to send U571 to a watery grave . 

 

Talking of U-boats this is a good watch:

 

 

[Onoff]

Do you have to increase the fall angle if the run isn't straight, say an L shape?

[PeterW]

No but any change in direction should be as smooth as possible - 90 should be 2 45s etc 

[Nickfromwales]

Or a swept / long radius bend better again . 

[Onoff]

36 minutes ago, PeterW said:

No but any change in direction should be as smooth as possible - 90 should be 2 45s etc 

 

This was the "agreed" drawing. I don't have the height for a swept bend:

 

 

Which I've translated to this: