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Posted: Wed Dec 30, 2009 12:27 pm
by seanandruby
As flo' says: that's an interceptor on the out going pipework. A back drop will be on the incoming pipework of the next manhole downstream. Usually you can put them in with extreme falls, ie 1/10.http://www.pavingexpert.com/images/drainage/dshaft01.gif
Posted: Wed Dec 30, 2009 1:28 pm
by Kevin10
thanks for all your advice. I've booked a drainage engineer to carry out a cctv inspection tomorow AM.
I sincerely hope it's not 10 ft deep. But surely if it were that deep, would Thames water insist that i excavate to that level? I wouldn't have throught that the load on it would be that great.
What gets me is that there are loads of rear extensions on my street which were probably done under Permited Development and never submitted an application to THames water in the first place.
Fingers crossed for tomorrow.
Posted: Wed Dec 30, 2009 2:58 pm
by flowjoe
You would think for a single storey extension that a raft would suffice over a 3mtr deep sewer but i have been on a site where they insisted the founds started below sewer level in order to bridge the load. Had a major affect on the price !
Had another guy who when digging out the footings found a manhole covering a sewer running straight through his extension footprint, unitied utilities told him to have the sewer surveyed and charted.
The sewer needed cleaning first (tanker jetter) and we surveyed it and did a plan of the site, total cost to the guy for investigations works just under 1K.
Nothing wrong with the sewer and they still refused him permission to build over the pipe, no matter what spec his architect came up with.
Bless em 
Posted: Wed Dec 30, 2009 3:18 pm
by Dave_L
Bunch of bastards, I reckon if a brown envelope passed hands at the right time, permission would have been granted.
Posted: Wed Dec 30, 2009 4:54 pm
by lutonlagerlout
theres a hill in Luton called hart hill, 1 poor bugger had his invert checked and it was 7M below DPC
he had to have it piled and a ring beam built
not good
LLL
Posted: Thu Dec 31, 2009 9:52 am
by Kevin10
The drainage contractors just left. THey just put a camera in there and all was clear (it was surprisingly clean in there!)
It's only 1m max underground.
I guess that's good news right? The building contractors will have to bridge over the sewer pipe... Does anyone have any links to show how one does this exactly?
Lesson from this saga - forget about Thames Water's (or any other water company) sewer map and their surveys - it cost me £50 and had bug*er all information and what little was there had a disclaimer stamped all over it.
Save your money and go for a survey for £100. Wish i'd done this earlier.
Posted: Thu Dec 31, 2009 12:18 pm
by mickg
you use 150mm x 100mm concrete lintels, seeing as the sewer pipe is 1m below ground level the foundations need to be below the invert level (the bottom of the sewer pipe)
build up the brickwork/block work with at least 50mm space between the top of the pipe and the underneath side of the lintels
your building contractor should know how to do this
Posted: Fri Jan 01, 2010 9:27 am
by Dave_L
Thanks for coming back and letting us know how you got on - Happy New year!
Posted: Sun Jan 03, 2010 11:46 am
by Kevin10
Hi guys, thanks for your help & very happy new year to you all. It turns out my extensioon designer will not provide the detail i need to make the application to Thames water to build over the sewer.
So i'm having to research and come up with the detail myself. Found some useful information online. Particularly the detail on the top of this page:
http://www.pam.ealing.gov.uk/PlanNet....1_A.PDF
Is this box around the drain pipe effectively what i will be aiming for? With 50mm clearance around the pipe for settlement and the lintels going over the top...
If i show this detail with dimensions, Do you think this will be enough for Thames water to approve?
The lintels that mickg described also sound a little small .. the dimensions are like tiles..(?) it's a 150mm drain pipe btw
Once again, many thanks gents.
Posted: Sun Jan 03, 2010 12:38 pm
by mickg
the lintels I described are used to carry brickwork/blockwork are are available from most builders merchants, these have been used time after time in this situation
the lintels are 150mm x 100mm x the required length
What a concrete Lintel looks like 
so its 150mm high 100mm wide reinforced with steel and what ever length you need to rest the lintels onto the brickwork allowing a minimum of 100mm each side sat onto the brickwork to distribute the load onto the new wall
they are going to be approx 600mm - 700mm long including 100mm each side to rest on the brickwork, measure the length you require and its sometimes more cost effective to purchase a longer lintel and cut it in half
Posted: Sun Jan 03, 2010 1:11 pm
by Kevin10
D'oh!
Posted: Sun Jan 03, 2010 1:17 pm
by lutonlagerlout
those lintels are called R15s
LLL
as mickg says we use them all the time underground
Posted: Sun Jan 03, 2010 1:38 pm
by Kevin10
superb. I've read the building regs downloaded from the planning portal :
http://www.planningportal.gov.uk/uploads/br/BR_PDF_ADH_2002.pdf
and diagram 7 on page 16 gives a useful sketch and some dimensions.
So basically i'll illustrate the following the application:
1) box around the pipe with 50mm clearance around the pipe - achieved by shuttering during concrete pour
2) Compressible fill (gravel or expanding foam) to fill the box
2) R15 Concrete lintels over the top
3) Concrete over the top & build as normal..
Does this sound ok?
Posted: Sun Jan 03, 2010 1:54 pm
by mickg
that sounds OK
the only change i would make is on your drawing you say your installing rodding eyes for any drainage junctions, you need to install a manhole for any change in direction or where drains join together, one to conform to building regs and the other for you own good, i noticed its going to be flats and you know what means don't you.....blocked drains !! 
Posted: Fri Feb 19, 2010 4:46 pm
by Kevin10
Hello everyone. Just wanted to write to thank you all for your help. I called thames water today and they've said my application has been approved.
Though they did want 2 applications for the adjacent properties that i was carrying out as one project. I'm sure the extra £343 pounds i had to pay them had nothing to do with it.
