New soil stack

[highleigh]

Of all the jobs in the renovation this is the one I am least confident about and I am very aware regs are quite strict and don't seem to be that easy to apply. I do have buildings regs notice so just want to ensure I am doing the right thing before I get the them out for this. Any advice will be much appreciated.

I am putting in a new stack for a downstairs wc and upstairs ensuite. One is above the other so I intend to have them both off the same stack.

There is Manhole cover is about 2m away from the base of the stack off to one side. There is a 110 clay pipe which is not used (old wc) which comes flat in to the base of the manhole at 45 degrees to the direction the new pipe will be coming from. Manhole is 90cm deep. To make this very simple I could have an outside stack which goes down almost 90cm, bend going to horizontal towards manhole inlet and then a 45 degree flat bend to join up with the existing inlet. I am not really keen on this as, I think outside soils stacks look ugly and I intend putting external insulation one day (solid brick)

I do have space for an internal stack but am unsure of the regs for getting the 110 pipe outside as it will include more bends. I doubt I will able to dig down 90 cm in the floor of the house but have already dug 25cm into the floor of the wc and could go a bit deeper. So as I see it the stack could be inside, 90 degree turn to go out through the wall, 90 degree back to vertical, 90 degree turn to run parallel to the wall toward the manhole then flat 45 degree turn to connect to the existing pipe. Main question is does this conform to current regulations and is there anything I should be aware of? Even if I wanted to put in any additional inspection chambers I can't see where I would put them.

Hopefully my message makes some sense. Any advice on this would be great as I am continuing digging tomorrow. Currently down to about 50 cm outside.

Thanks,

 

[Hugh Jaleak]

Can you access the existing pipe in the old W.C. to make a connection to that? Bends in the wet part of a stack are best avoided, ideally you want to achieve a straight drop into a rest bend at the foot of the stack to the sewer.

It is doubtful Building Control would allow your proposal with that many bends in it. Bends are allowed immediately outside a manhole, elsewhere could be frowned upon as rods wont go round should a blockage occur.

 

[highleigh]

No, can't use the old soil pipe, there is a back door in between the two locations. In any case the old soil pipe was retro fitted in the way I have just described, found that out when doing the excavations.

Going from the drop straight to sewer is almost impossible for an existing building. Is the standard way of retro fitting an internal soil stack?

 

[Hugh Jaleak]

It's not impossible to fit a new stack internally, main issues are bridging the pipe where it passes through the foundations and digging the hole in the internal floor. It may be advisable to discuss ideas with the BCO, they'll inform you what they expect to see done.

If you need to change direction underground then look at shallow inspection chambers. These would allow the required access if needed.

 

[highleigh]

thanks, digging floor should not be a problem. I have dug up all the floors to put in insulation and ufh. All screeded except for this last room as it was previously the boiler room, only accessible from outside.

having dug some more outside this morning I have come across an old wall foundation 20cm from my outside wall. this about 60cm below inside floor level.

Main reason I had not previously considered shallow inspection chambers before was I couldn't see how the soil pipe would then drop to the base of the manhole. could I simply cut into the wall of the manhole and put in a bend and vertical pipe inside the manhole? I could quite easily direct the flow neatly. shallow inpection chamber could then easily be used to turn the 90 degrees towards the manhole. I still have the option for internal or external soil pipe.

I've taken some pics and will put them up later, I'll also give BC a call but rather than ask what to do I want to be in a position to tell him a realistic plan.

probably going to stop digging now and carry on with a bit more insulation in the dorma roof.

 

[highleigh]

Here are a couple of photos from the digging this weekend.

Currently dug down about 70 cm from top of manhole.

Soil Pipe excavation

• highleigh
• 21 May 2012
• 1

Manhole is at the end of the trench. New soli pipe will start where the hose reel is. Either...

You can see the old wall foundations in this picture.

Soil Pipe excavation

• highleigh
• 21 May 2012
• 1

Old drain which will come out. It has a trap and was previously used for the washing machine and...

The existing drain is coming out as it is not used and was for the washing machine and a sink. Solid pipe will come down the wall where the hose reel is, either inside or outside. and go towards the manhole.

I need to go down about a meter to join up with the bottom of the manhole or I can have some kind of backdrop, inside or outside the manhole. That way I imaging I could put the soil pipe inside. Come out of the wall about 50 below floor level, 40 cm below ground level, put in a shallow inspection chamber for the 90 degree turn toward the manhole, then a backdrop at the manhole.

I'll try and explain this to BC but big question is internal or external backdrop? Any suggestions, there are some comments on the web that internal ones are frowned upon?

Note: old downstairs wc was where the hole is by the manhole at the corner of the building. The old soil pipe comes out the wall higher up and then drops with no inspection chamber then goes to the base of the manhole. I could reuse its entry into the manhole.

 

[Hugh Jaleak]

If there is an existing redundant connection into that chamber then i'd use that, will save an awful amount of effort breaking in to fit a new connection. Providing the pipe is in good condition, carefully cut it back at a suitable point and use an appropriate coupling to join to it. Slow radius bend should point you in the right direction, then run drain to new chamber position.

You may get away with using a couple of slow bends to lift the drain slightly in a 'dog leg' fashion to suit an invert of 600mm for the shallow chamber, a 400mm invert may leave the pipework vulnerable.

 

[highleigh]

Thanks for showing an interest Hugh, your help is much appreciated. I'm doing a lot of additional reading/google searching the more I understand what is required.

Agree unsing the redundant connection. It looks good enough to me and was in before I took the old wc out. It runs into the chamber at 45.degrees so will require a bend but I can't see this being a big problem. Unfortunately the invert is about 100cm. I can't see how I can drop from even 60 to 100 even with a couple of slow bends in just 250cm from the base of the stack to the chamber. (unless there is something I dont know about required gradient?) hence why I thought I needed a backdrop.

As for minimum invert, is there any guidance on this. I haven't seen this anywhere?

Thanks again.

 

[Hugh Jaleak]

Recommended fall is 1:40 on 4" drain, but you can sometimes 'cheat'. If you fit a slow bend to point the drain 'upwards' then another to get it back on the horizontal immediately before the new chamber, BCO might just allow you to get away with it, rather than making a new connection into the chamber. Main issue is achieving a 'self cleansing velocity' in the drain, you dont want the s**t flying into the chamber and splashing everywhere fouling the benching opposite.

Building regs part H has guidance on cover for pipes. http://www.planningportal.gov.uk/uploads/br/BR_PDF_ADH_2002.pdf
If drain is under a path then not so vital, but under a driveway or garden then protection is vital to protect the pipe from weight of vehicles or gardening damage.

 

[highleigh]

BC has been round and said I should come away from the house, put a small shallow inspection chamber over the bend towards the drain and then put in an external backdrop next to the manhole. Sounds pretty reasonable and means I still have the option of internal or external soil pipe.

All seems so simple now so thank you so much for the advice.

Can anyone recommend an inspection chamber over a 90 degree turn? It will be about 40 cm deep and is in the alley by the side of the house so no cars going over it,

Thanks.

 

[Nige F]

Can anyone recommend an inspection chamber over a 90 degree turn? It will be about 40 cm deep and is in the alley by the side of the house so no cars going over it,

Thanks.

OSMA 4D918

 

[highleigh]

Well I bought the parts and dug down the side of the manhole to put in the back drop. I had thought one of the inlets into the manhole was unused, as it was the old downstairs wc but i find a tee with on going to the old wc and the otherwise going to the rain water drain at the front of the house. To make it worse the pipes are clay and the tee is cracked just where it goes into the manhole.

I now have a couple of quandaries.

I could cut out the old clay pipe going into the manhole enough to put a plastic pipe back in the hole. This channel sits on the lip of the straight pipe running through the manhole so I don't have a problem of joining the two channels here. Is this OK? This will make good the cracked pipe and remove the old wc connection.

I don't have and space to create a new channel into the manhole so will have to connect my new wc to this pipe. Plan was for a backdrop to this pipe when I thought it was just for the WC but can a backdrop join an existing pipe when it drops? Another option is to put in a new drain run from the from the rain pipe at the front but not so deep, then join it to my new wc pipe inspection chamber, as it comes from that direction and then proceed as before.

I try and put some photos up but does anyone have any other suggestions.