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Dodgy-diver

I think its all gone wrong

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so I plan on building a 3 meter deep rear extension under the permitted development scheme 

 

I have just started digging out foundations by hand and come across the main toilet drain that runs accronn the back of all the properties in this row , its a 1915 house and the pipe is only 240mm below finished floor level 

 

it can not be moved as it serves more than just me , the manhole in the garden is only 380mm deep 

 

please can anyone offer me any light here , im gutted 

thanks 

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Pictures would help

Id a similar issue at our last house 

The pipe ran along the trench is was digging 

So it was a case of knocking on doors and asking neighbors not to use there loos while I moved the 12 mtr length of pipe and added  a inspection chamber 

If it had crosse the trench BC would of allowed me to put a concrete lintel in and simply build over 

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28 minutes ago, Dodgy-diver said:

I can not move this as it serves a lot of houses and the fall is so slight Pictures would help 

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22 hours ago, Dodgy-diver said:

so I plan on building a 3 meter deep rear extension under the permitted development scheme 

 

I have just started digging out foundations by hand and come across the main toilet drain that runs accronn the back of all the properties in this row , its a 1915 house and the pipe is only 240mm below finished floor level 

 

it can not be moved as it serves more than just me , the manhole in the garden is only 380mm deep 

 

please can anyone offer me any light here , im gutted 

thanks 

Can't see that you are going to have a problem provided you are careful excavating around it - your concrete will stop short of that level and you can just stick a lintel over it when building the walls.

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I would say step up into the new bit or raise floor level. 
 

I would replace it in plastic , any manholes outdoors 

 

 

Edited by tonyshouse
Added phrase

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And while you are at it, offer your loo for anyone in the row who is desperate. Good PR: nobody will take you up on it.....

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23 hours ago, Dodgy-diver said:

so I plan on building a 3 meter deep rear extension under the permitted development scheme 

 

I have just started digging out foundations by hand and come across the main toilet drain that runs accronn the back of all the properties in this row , its a 1915 house and the pipe is only 240mm below finished floor level 

 

it can not be moved as it serves more than just me , the manhole in the garden is only 380mm deep 

 

please can anyone offer me any light here , im gutted 

thanks 


You can build over this but it needs some thought and also will need permission from your  sewage provider. 
 

Assuming this is a terrace, how many houses upstream of you location ..?

 

if the pipe is 240mm below FFL then it will just be below your insulation level assuming a standard build up of 100mm MOT, 100mm PIR and 100mm of concrete as slab. 
 

Couple of ways to approach this, neither are “fun” but can be done in a couple of hours if you have a couple of good friends ..! 
 

Assuming the manhole is downstream of your extension (given the depths) you need to make friends with your upstream neighbours. 
 

First job - expose the whole of the top of the pipe (assuming this is clay) and measure the distance from side to side of your extension and add 300mm each side. That’s your replacement length. You need enough UPVC pipe to do the length you’ve identified. Mark the points you’ve measured, and ensure you have 150mm either side of the mark to put a connector. You’ll be using clay connectors so plenty of lube on the pipe and they will go in easy. 

 

Dig carefully around the pipe where your marks are - you want 4-6” below the pipe clear. It is nicer doing this now rather than later. 
 

Now get the jet wash out, and get it in the pipe from the manhole and jet the whole length as it makes the next job much nicer ..!

 

This is where you need friends ...Ask the neighbours nicely and basically you need to block the drain for an hour. 

 

In the upstream manhole, on the upstream side of the manhole, insert a bung in the pipe, lock it up tight and put a couple of bits of timber in the channel to wedge the bung and stop it sliding.Tie a loop of rope onto the handle on the bung - this stops it getting lost if you do get a release. Tie it to a bit of timber and leave that outside the manhole.  Chuck the hose into the manhole and wash down the pipe to make sure there is nothing nasty lurking in the pipe. 
 

Now on the marks you’ve made take a Stihl saw and cut through the top mark. It needs to be a clean straight cut so take your time. From this point, Mate #1 can start digging out the old pipe, just pull it out and clean the trench as you go. Keep going and make the second cut on your second lower mark, try not to disturb the connection into the manhole. Dig out the remains of the pipe, get the trench as flat and clean as you can but don’t panic too much. You need to get 2-3” of fine gravel under the pipe but don’t worry too much at this point.

 

Mate #2 now needs to do a semi dry mix of 3:1 ballast and cement. You need 2 or 3 buckets full. Drop a shovel full every 3 ft along the bottom of the trench, this is for bedding the pipe onto. 
 

Now put the clay connectors onto each end of the uPVC and drop your uPVC pipe into the trench, and slide the connectors over the clay stubs. Do up the bands and using a string line check the new pipe is flat if it has a join in it, and use a level to make sure you have a fall from one end to the other. if you need to move the pipe about, just bed it further into the concrete or add a bit under the pipe. 
 

Once you have your levels, hose back in the upper manhole and check for leaks. Drop the rest of each bucket of concrete over where you’ve bedded it, and then it’s the fun job ... 

 

Take your prop timbers out, and then slacken the bung. Chances are it will wash out so be ready, and just pull it out with the rope. 
 

You’ll get a surge down the pipe but nothing that should cause issues. Time for a cuppa and a chocolate hobnob.. 

 

Double check your joints are still dry, and now back fill below the joint and the pipe with 10mm pea gravel. You only want to go 1/3rd of the way up the pipe as you’re going to be encasing the rest in concrete as this will give more protection to the pipe, the joints want to be only in pea gravel as it can allow a little movement then. For the concrete around the pipe a 4:1 mix will do, just pack it round the pipe then over the top, just don’t go mad and make sure it’s below 220mm of the FFL. 
 

when you come to do the rest of the founds you can dig round this and cast under with the concrete, just put a lintel over the top where brickwork goes over it. When you’re laying the MOT, don’t run the whacker over the pipe but just cover that area with sharp sand. 
 

Photos would be helpful btw..!
 

 

 

 

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