Foul Drainage Basics

[MortarThePoint]

For 110mm foul pipes running around the outside of the house I was expecting to dig a trench about 300mm wide, put down a bed of pea gravel and then fill to just covering the pipe with same gravel. Then topsoil over all that. Does that sound the right approach?

 

If I understand part H diagram 10, this method meets or exceeds Class B as long as the top of the pipe is at least 150mm deep. Though not sure why the vertical sides of the trench continue upwards in the diagrams. I think my shallowest pipe would have it's top at about 150mm below the surface.

 

What I'm less clear on is how far from the wall to have the pipes. All pipes are above top of concrete foundations. Further from the house feels like it leaves room for unknowns, but perhaps gets closer to somewhere the wife might stick a spade.

 

I guess same question applies to rainwater drainage too.

 

[dpmiller]

Bedding is only for supporting the pipe and the diagram reflects that. If the pipes are shallow then there's another section to read w/ concrete casing or slabs over the top for protection?

[MortarThePoint]

Oops, those 'Rigid' pipes are only clay, concrete or iron. The normal brown/orange PVC pipes are classed as flexible. That changes the normal installation to as shown below, (b). That suggests a minimum depth to the top of the pipe of 300mm which could be tricky.

 

 

[MortarThePoint]

3 hours ago, dpmiller said:

Bedding is only for supporting the pipe and the diagram reflects that. If the pipes are shallow then there's another section to read w/ concrete casing or slabs over the top for protection?

 

Depth information is only given for where vehicles may travel, like fields and roads:

 

 

And if that can't be achieved, a slab used

 

[MortarThePoint]

This is the setup I am trying to work out. Unfortunately the 450mm inspection chamber exists in the wrong direction. I'm hoping I can put a tee right next to it to solve that, since the long straight run will be roddable from the 300mm inspection chamber bottom right of diagram. I'd prefer something smoother, but can't find a product that is a 'resting bend tee' equivalent. Does this look at all sensible?

 

The existing 450mm inspection chamber has an outlet invert 600mm below the surface. 1:40 fall would necessitate 600mm - (15,000mm/40) - 2*(300mm_chamber invert steps) < 225mm.

 

Noticed a product called a shallow access 90 degree chamber which avoids the steps at the two 300mm chambers: https://www.drainagesuperstore.co.uk/product/280mm-dia-90-degree-shallow-access-chamber-base-110mm.html

 

@Nickfromwales do you get involved in the mucky pipes outside or just stay warm inside?

 

[Nickfromwales]

2 hours ago, MortarThePoint said:

This is the setup I am trying to work out. Unfortunately the 450mm inspection chamber exists in the wrong direction. I'm hoping I can put a tee right next to it to solve that, since the long straight run will be roddable from the 300mm inspection chamber bottom right of diagram. I'd prefer something smoother, but can't find a product that is a 'resting bend tee' equivalent. Does this look at all sensible?

 

The existing 450mm inspection chamber has an outlet invert 600mm below the surface. 1:40 fall would necessitate 600mm - (15,000mm/40) - 2*(300mm_chamber invert steps) < 225mm.

 

Noticed a product called a shallow access 90 degree chamber which avoids the steps at the two 300mm chambers: https://www.drainagesuperstore.co.uk/product/280mm-dia-90-degree-shallow-access-chamber-base-110mm.html

 

@Nickfromwales do you get involved in the mucky pipes outside or just stay warm inside?

 

Lol. 
 

I’m in the trenches, so to speak, at the moment.

 

I’m not shy of anything, as no job is beneath anyone, afaic. 😉

[crispy_wafer]

Shame about the existing 450, I know the image isnt to scale, but my thoughts before seeing the ‘existing’ text was spin it around, get it in line with the 300 and stp, have the two outlets from the house come in on side branches, with the main through flow run straight through from the 300 to the STP.  Regards the tag on the treatment plant thread, Sorry, I’m still knocking my way through the build so it isnt in use yet.

[saveasteading]

Do you have a drawing showing depths and gradients? I'm not following the problem atm.

[ProDave]

I suspect you would want a new IC right next to the existing 450IC so you have rodding access.  

[Russell griffiths]

My ten cents worth

the inspection chambers on the two 90 degree turns, fit 45degrees bends to the chamber 

you then in effect turn the chamber into a slow radius bend instead of a sharp 90. 

[MortarThePoint]

1 hour ago, ProDave said:

I suspect you would want a new IC right next to the existing 450IC so you have rodding access

 

Should be roddable via the bottom right 300mm inspection chamber (IC).

 

1 hour ago, saveasteading said:

Do you have a drawing showing depths and gradients? I'm not following the problem atm.

 

The main challenge is the exit of the 450mm IC facing the wrong way. I spoke to my BCO and he said he'd be ok with a Y-tee and 45. I think I'd make the 45 by cutting a resting bend and that way I can fine tune the angle.

[ProDave]

1 hour ago, MortarThePoint said:

Should be roddable via the bottom right 300mm inspection chamber (IC).

But that is 9 metres away and if the blockage is downstream you will need 30M of rods.  I am sure BC wants rodding points closer than that?

[saveasteading]

The bco prob hasn't had to deal with blocked drains. Multiple bends coupled with shallow or steep falls, and stuff gets left behind.

[MortarThePoint]

Important to remember my rocker pipes, but less clear how to do that on the 450mm with Y-tee arrangement.

 

[Russell griffiths]

19 hours ago, ProDave said:

But that is 9 metres away and if the blockage is downstream you will need 30M of rods.  I am sure BC wants rodding points closer than that?

30 m is the maximum distance between chambers if I remember rightly. 

[MortarThePoint]

1 hour ago, Russell griffiths said:

30 m is the maximum distance between chambers if I remember rightly. 

 

I don't want to go too far between ICs to make clearing blockages easier, but aren't the regs 45m between ICs:

 

 

I think I'd break the ~20m section in half with another inspection chamber in case rodding through the STP was difficult

[saveasteading]

39 minutes ago, MortarThePoint said:

rodding through the STP

You don't.

So a chamber just before it is a good thing. In fact it's likely a standard detail for the STP.. I haven't checked. 

[Russell griffiths]

I think all this drainage is a bit 1980’s based any company coming to unblock something will have a jetter, they are not rodding it. 
but the regs are the regs I suppose. 

[saveasteading]

14 minutes ago, Russell griffiths said:

 company coming to unblock something will have a jetter, they are not rodding it. 

I have a jetter  but would choose to rod it first.

That way I would feel where the problem was and note for a remedy or the future.

Also it won't burst any poor joints or old pipes.

So the regs are sensible I think.