40mm into soil pipe - need a trap?

[speakermonkey]

I have a permitted combined sewer, so the rain water can go into the waste water sewer. I have all the bits ready to take the gutter down pipe (currently just going straight onto the ground, ) and connect it to the soil pipe (so 68mm -> 40mm then into existing soil pipe). My question is - should I consider fitting a u-bend trap to the 40mm pipe before it connects to the soil pipe? The gutter is 4m high and outside, and it is fairly windy where we live, so I am not sure there would really be a problem with smells. The sewer manhole covers don't emit smells after all. I'm thinking it would probably be overkill.

And is there anything else I should be considering?

Thanks

 

[Dereekoo]

Unless you have a particular troublesome smelly sewer then no. manhole covers may be airtight but that is something else. Don't know what a permitted combined sewer is, its either a combined sewer, a foul sewer or a surface water sewer

 

[Dereekoo]

Unless you have a particular troublesome smelly sewer then no. manhole coversmay be airtight but that is something else. Don't know what a permitted combined sewer is, its either a combined sewer, a foul sewer or a surface water sewer. And in theory the WC should be informed of any new discharge to their system ( but they will never know)

 

[Madrab]

And is there anything else I should be considering?

Is there any provision for catching and cleaning any crud/debris/leaves/etc from the roof/gutters before running into the soil pipe and rodding into the soil pipe. If not then not sure it's the best idea to drop the guttering to 40mm and then into the soil pipe directly. Have BC ok'd that idea?

 

[speakermonkey]

Unless you have a particular troublesome smelly sewer then no. manhole coversmay be airtight but that is something else. Don't know what a permitted combined sewer is, its either a combined sewer, a foul sewer or a surface water sewer. And in theory the WC should be informed of any new discharge to their system ( but they will never know)

Thanks. Yes, it's a combined sewer, but we applied for it as it was originally just a normal foul water one.

 

[speakermonkey]

Is there any provision for catching and cleaning any crud/debris/leaves/etc from the roof/gutters before running into the soil pipe and rodding into the soil pipe. If not then not sure it's the best idea to drop the guttering to 40mm and then into the soil pipe directly. Have BC ok'd that idea?

Yes there is a leaf guard in the gutter exit. Thanks.

 

[Dereekoo]

Thanks. Yes, it's a combined sewer, but we applied for it as it was originally just a normal foul water one.

So although it was just used for your foul drainage I assume it fed into a WC combined system or I would doubt that the WC would allow such an addition

 

[Ivor Windybottom]

You should never reduce diameter as you go downstream, it should only ever increase. You can't fit that 68mm-40mm connection, that will be a guaranteed future blockage, even just from the silt that would get past the leaf guard. Also, even if it doesn't block then it will definitely restrict the flow, so will back up in heavy rain.

If you were to directly couple the downpipe into the sewer (without the 40mm restriction), then the downpipe would become a sewer vent. You'd get bad smells from the gutter, particularly in the summer when there's not a lot of rain to keep things clean and the stuff within it is fermenting. Also the downpipe itself isn't sealed, they don't have o-rings, the joints just basically pour into the next one like a bottle pouring into a funnel. So all joints on the downpipe will also smell.

I very much doubt that a building inspector would approve of what you're planning, because of both the 40mm restriction and the lack of a trap. A proper sewer vent is a sealed pipe that goes up much higher than the gutter and a prescribed distance from windows. You can't put water from the gutter into a vent pipe, as it would then vent at gutter height so not allowed.

You should fit a bottle gully to the sewer, then your downpipe runs into this.

I don't know of a way to directly couple a downpipe into a sewer via a trap, as the trap needs access for maintenance. This is what a gully is intended for.

You can cut the grille on top of the gully and put the downpipe down through it. This is fine, in fact I prefer it as you won't get splashing out of it.

 

[Madrab]

Why do you want to feed the rainwater downpipe into the soil pipe in the first place? If I remember my regs properly, there is also a limit to the amount of roofspace can be drained into a discharge stack, if allowed at all. The reason for that is too much rainwater discharged into the sewer can overwhelm them leading to sewage being discharged into rivers etc and LC's are really trying to avoid that now, if you have the approval though then fair enough, as there are still 1000's of combined systems.

The reason for the questions though is it's unusual for a rainwater downpipe to be actually connected to a discharge stack, that and as suggested, the rainwater pipe then becomes a vent for the soil stack and the vent would need to be open above the gutter level with the downpipe then connected in below the gutter. As a professional it's not something I would design unless there were absolutely no other options.

Also as suggested a leaf guard is not a foolproof device to ensure there is no ingress of material into the stack, that coupled with the narrowing may cause issues.

 

[Ivor Windybottom]

The reason for the questions though is it's unusual for a rainwater downpipe to be actually connected to a discharge stack, that and as suggested, the rainwater pipe then becomes a vent for the soil stack and the vent would need to be open above the gutter level with the downpipe then connected in below the gutter. As a professional it's not something I would design unless there were absolutely no other options.

It's not physically possible to run a gutter into a vent stack without this opening becoming an air vent at or below gutter height, which is not allowed. This makes using a vent stack as a downpipe impossible.

Definitely go right back to the drawing board on this project.

 

[speakermonkey]

It's not physically possible to run a gutter into a vent stack without this opening becoming an air vent at or below gutter height, which is not allowed. This makes using a vent stack as a downpipe impossible.

Definitely go right back to the drawing board on this project.

Hmmm, okay. I'll try and get some photos of the layout so hopefully it will make more sense as to what I'm trying to achieve. Installing a bottle gully is not an option due to the weird layout of the building.

 

[speakermonkey]

Okay, so I should have shown this earlier, but never mind. Here is my current plan

Red line = 68mm guttering
Blue line = 68mm -> 40mm adaptor and connection to 4" waste pipe. So there will be very little length of the reduced diameter.

The vent is inside the lean-to out building and the sewer manhole is on the other side of the lean-to building.
Currently we are emptying the bin-bucket after it rains, where the pipe originally went is anybody's guess as it had soil built up 5' high inside.
The only other alternative I can think of is to install a bottle gully on the other side of the lean-to gutter you can see in the foreground (also this downpipe is a mystery) and change the rise so the water flows from right to left, and somehow connect the main roof's drain to that.

Any suggestions welcome. Thanks for your help.

 

[Madrab]

I guess the other indicator that it isn't an established nor approved approach is that you don't get a 68mm (2 1/2") to 110mm (4") adapters outside of ebay. If it was an established process then they would be freely available.

Having a look at your layout, what is the ground type like, is it suitable for a soakaway? What's at the other end of the guttering at the front, could a downpipe be used there?

I think you need to do a bit of digging and see how everything is laid out. The original downpipe was probably clogged full of everything for years of stuff from the gutter and you may find there are still main drain connections underground that just need cleaned out. The ideal would be to re-establish them.

 

[Hugh Jaleak]

Photo is very useful, thanks. Put simply, you cannot connect the rainwater to that soil pipe.

Your options are, trace the soil pipe down, find where it goes underground and couple onto the sewer there at a suitable point, run back to somewhere in that external space and provide a trapped Gully, into which the rainwater downpipe can go.

Or, where does the other downpipe in the left foreground go to? Any option to connect to that? Looking at the age of the property, I'm in agreement with Madrab, and would expect there to be some form of drain provided at the bottom of the downpipe, chances are its either clogged up or someone has disconnected the original downpipe to divert to a water butt, and the end is buried underneath the bin.

 

[speakermonkey]

I guess the other indicator that it isn't an established nor approved approach is that you don't get a 68mm (2 1/2") to 110mm (4") adapters outside of ebay. If it was an established process then they would be freely available.

Fair, I got the adaptor from Amazon.

Having a look at your layout, what is the ground type like, is it suitable for a soakaway?

Weald clay - very expansive and shyte at draining, we don't have the space either - hence the application to a combined sewer.

What's at the other end of the guttering at the front, could a downpipe be used there?

That goes straight onto the ground also. The plan was to have the whole gutter draining to the rear downpipe (the one in the photo), to avoid having to do a job both ends. But this may be the solution - see below.

I think you need to do a bit of digging and see how everything is laid out. The original downpipe was probably clogged full of everything for years of stuff from the gutter and you may find there are still main drain connections underground that just need cleaned out. The ideal would be to re-establish them.

I have done, we have actually had a full drainage survey done when we moved in 2020. I don't believe the surface water drainage has been looked at since the building was built over 150 years ago (as a stables!). Without writing a short detailed essay on it all we were quoted around £30k (by two companies) to re-establish all the drainage back to working order. The original surface drain is supposed to drain into a brook about a quarter mile away - safe to say this system is well and truly dead.

This is one part of a much larger overhaul, but it is probably the trickiest bit. A few builders we've had round to do other things agreed that this was the simplest option. It wasn't my intention to open a can of worms on this thread, I was just worried about the smell. Things are never as straight forward as you'd like them to be.

Photo is very useful, thanks. Put simply, you cannot connect the rainwater to that soil pipe.

Your options are, trace the soil pipe down, find where it goes underground and couple onto the sewer there at a suitable point, run back to somewhere in that external space and provide a trapped Gully, into which the rainwater downpipe can go.

Or, where does the other downpipe in the left foreground go to? Any option to connect to that?

Just straight into the ground, but it is fully blocked like the r.hand one was and I haven't had the heart to find out any further. I'm not too bothered about this one as this will be getting knocked down and rebuilt at some point.

Looking at the age of the property, I'm in agreement with Madrab, and would expect there to be some form of drain provided at the bottom of the downpipe, chances are its either clogged up or someone has disconnected the original downpipe to divert to a water butt, and the end is buried underneath the bin.

The end is non-existent. See above.

It may be case of trying to take it from the other end - this was my original proposal to my wife, but it meant a large diagonal pipe going across the front of the house, so she said no. I think I could install a gulley on the front of the house and an underground pipe from there into the old knackered surface water drain and hope for the best, but this is more work that I was hoping for.

Thanks for the input, I really appreciate it. I will mull on my options a bit further.