Cloakroom WC drainage plan

[Hugh Jaleak]

Existing chamber is designed clearly to accept an inlet at that point, however it's not something I'd have imagined to work for foul drainage, for the simple reason it could allow solid matter to build up. It would partly depend on the velocity of the incoming flow, I've seen the bigger 450mm chambers where a stack is connected quite close to the chamber, and the resulting mess where the solids have hit the bend at the bottom of the stack and get flung into the chamber, and indeed have even known these setups to have to be replaced with a traditional brick chamber in order to alter the arrangement and prevent the issue, such were the number of issues they were having! (This was a Public Building though, so the WC(s) was (were) probably in much greater use and there's less control over whats put down them!)

If you're happy to risk it, then cut a hole to suit in the side of the current chamber, bring your new pipe in, and for belt and braces, I'd put a bend on the end to direct the flow towards the outlet, which should prevent too much 'spatter' on the opposite side. I'd probably be tempted to try this for a while and see how it fares. If you find you are having issues, then maybe time to look at altering the chamber setup.

You should be ok without venting, its perfectly acceptable to connect a WC directly to the drain provided the depth from the Crown of the WC trap to the invert (bottom edge) of the drain doesn't exceed 1.3m. I would be slightly more concerned if you connected to the stack in your situation as you're below the accepted connection point, which is 450mm above the invert of the drain at the bend at the foot of the stack.

To remove the chamber would mean digging around it, cutting through either the inlet or outlet to free one side off, and then pulling the chamber off the other end. To graft new chamber in, fit a stub of 110mm pipe to the required end, push it back onto the original stub you've pulled the current chamber off, then use a slip coupling to make the connection with the cut end of the other pipe. Connect in existing and new laterals as required.

 

[swilli88]

Such a helpful and thorough response! thanks again! yep as you said I think connecting to the current aj might be the easiest thing to do for now until there actually is a problem with foul build up. In which case theres nothing to prevent the digging up in the furture to fix properly (i can even jsut put hardcore around the new connection outside until its been there long enough without issue). All potential future corrections to the AJ then would be outside so theres no concern over indoor digging thereafter.

I think the route i will go with to the aj is option 1 above. Main reason being if im come out right beside the AJ theres actually very little room to work with the 4" pipe and bringing it out a little further away gives options for routing.

I didnt know there is a minimum height above the lowest bend approaching the aj that a connection can be made? thats 450mm? yes connecting to the stack would be significantly lower closer to that bend than 450mm

 

[Hugh Jaleak]

I'm basing things on UK Building Regs, but principles are the same, wherever. All rules are there for good reason, experience often tells you why!

 

[swilli88]

howiya @Hugh Jaleak

so iv made a lot of progress. trench is well and truly dug now. (pictures attached)

you will notice halfway through the trench, despite all of my efforts to locate and detect pipework prior to works, i hit a mains feed into the house. So that was a lot of fun and a scramble out to the road to stop the flood . Withe the help of a plumber friend and two trusty philmac couplers the mains feed has been restored and hours leak free so far. Not in a hurry to concrete this over until satisfied that those joints are sweet. the secondary issue with the mains feed discovery was that it was right in the way of where the soil pipe is meant to go so i dug an extra bit down and to the side to remove material beneath the pipe to allow it to flex very gently over a wide radius to naturally now go below the soil pipe-to-be. So as far as im concerned that setback has now been resolved.

Im sure ill have a few questions over the next couple days but the immeidate question is the order in which i should be backfilling the trench.

Is the damp proof membrane the first thing that goes down on top of the photos you see attached? whats the best way to try and integrate the new membrane with the edges of the old? would you ever suggest trying to overlap and tec7 them/seal them together as much as possible to try and restore fully that moisture barrier?

generally after that, what is the order of backfilling and supporting the soil pipe from here? i have gravel, builders sand, hardcore and plenty of rubble big and small from digging the trench? and then how thick should the top layer of the concrete be

 

[swilli88]

what do you think @Hugh Jaleak

 

[Hugh Jaleak]

Pipe will go beneath the DPM I am assuming?

Pipework ideally needs bedding in peagravel, I'd also haunch it over the top of the pipe. If room, then a thin layer of sand, (unless there is several inches to make up, so to economise on sand, selected material, (no lumps or large stones/bits of broken concrete), then a thin layer of sand), simply to protect the DPM from any possible punctures.

You haven't a lot of room to play with by the look of that, but your replacement DPM needs to overlap the existing as much as possible, then concrete/screed on top to meet existing finished floor level. Needs to be same thickness as the existing to maintain the strength of the floor.

 

[swilli88]

@Hugh Jaleak so the original layer of DPM is below the 6 inches of concrete there originally. For the most part the soil pipe will be above that level, with the exception of near the exterior wall where the fall takes it below. Does it make any sense to have a DPM below the soil pipe as well?

I had thought i would try and connect new DPM to the old as best as possible and then another layer of it right before the concrete? It will be near impossible to tie the new dpm into old ABOVE the pipe. do you understand what i mean?

by 'haunch' do you mean just build up the gravel to level near or covereing the pipe?

also since the original concrete was 6 inches think theres no way I can restored the slab to that level of thickness. I will have minimum of 2" (at toilet end). My thinking was that it might be better to have 2" of concrete the whole way along the run rather than it getting thicker towarrd the end of the run where theres space. Does that make sense or should i let it thicken as it goes down the run?

For replaceing concrete slab like this should it be a C20 or C30 concrete mix?

 

[Hugh Jaleak]

I think you're governed by the invert level of the existing drain which doesnt help matters. I'd be wanting DPM at or as near to, the level of the existing for ease of tying it in, for belt and braces, another layer will not hurt anything. As the drain needs to run above theDPM then so be it, but usual practice is to haunch over with concrete if drain is hallow to provide as much protection as possible. 'Haunch' means to bring up the material to hold or cover the item your installing/laying and prevent lateral movement.

I'd use C20 concrete, you need the extra strength, especially with a drain below it. Let it thicken where possible, for the same reason. Too shallow and you may risk it cracking.

 

[swilli88]

since writing earlier I have looked closer and it looks like I will be able to (in as best as possible where its torn by trenching) restore the DPM to the original ABOVE the soil pipe by slight arching its path across. So for the most part the pipe will be under the DPM.

The fall I am aiming for is about 1:80 as i read that between 1:40 and 1:110 are acceptable so to base calculations on 80. If it were you would you push it closer to the 1:40 or be happy with 1:80?

a friend of mine mentioned hes uses blobs of mortar in the trencht to suppor the pipe at the right fall? is that something you practice or to you think uneccesary?

 

[Hugh Jaleak]

You may get away with 1:80 provided that's constant and the pipe is perfectly straight. !:40 stems from the old days when salt glazed pipes and morater joints were used, but its still a good rule of thumb even today.

Feel free to use whatever method you prefer to set the pipe, some used to use bricks in the bottom of the trench, mortar is a new one on me, but as long as the rest of the pipe is bedded and protected with peagravel, I dont see an issue.

 

[swilli88]

ok thanks. think il manage about 1:60 so that should be ok.

a have a few bricks I can use alright so will do that i think.

before i concrete over this whole thing tomorrow, is there a typical way to test the 4" pipework other than throwing a bucket of water down?

 

[swilli88]

the gravel bags i just opened seem to have wet gravel in there. is that ok to use as bedding? @Hugh Jaleak

 

[Hugh Jaleak]

Wet gravel is fine. Air test is usual practice for testing tightness of drain, i.e. no leaks. Provided all the joints are made properly, and given there's no pressure in the run then chances of anything leaking are pretty remote usually. If you really want to check, put a bung in bottom end and fill the pipe with water, mark level, leave overnight and see if it has dropped by the morning.

 

[swilli88]

Yep thats a great idea to test. definite worst case scenario to have any kinds of pressure in the pipe.

When bringing the 4" out of the wall i am intending to have the non socketed end extend out the wall (i.e the male end of socketed pipe, essentially standard 4"pipe. Is the best way to do it? If it is does should I aim to have the socket of the push fit bend that go a little into the hole so that you cani can mortar 'lock' in place?

aside, does mulitlayer pipe (APE brand) need lagging in concrete?

 

[Hugh Jaleak]

Push fit joint should remain tight on the pipe, although you can mortar it in for aesthetics if you prefer, or if you need to bury the 'lip' into the wall to get the correct positioning on the pipework. I'd get it set, correct fall and make sure it holds a test before making good anyway!

Plastic pipe should be fine buried in concrete, it's used for underfloor heating where it's buried in the floor screed. Copper has to be protected, as the concrete attacks it, eventually causing the metal to corrode and fail.