I am afraid that I know NOTHING about drainage so please forgive me if this question is amateur.
We are currently buying an end of terrace house and we have just received the drainage search. It shows a private sewer that starts in 'our' garden and runs along the back of the house, just outside the back door where we were planning to build an extension.
The private sewer serves 6 properties and connects to the public sewer 6 doors down from us. The houses were built in 1963.
The burning question is can I (and would it be sensible) build over the sewer? If not, how much would it cost to move the sewer 2m further into the garden just outside where the extension would be?
Any help would be greatly appreciated as the lack of potential to extend the house would be a deal breaker and we would have to pull out the sale
I'm not someone who "knows" either, but, I watched a TV programme where they built an extention over the drain. They had an inspection cover inside the extension (all professional & sealed etc).
As I understand it the public ones are "sewers" and the private ones are "drains".
As you are at the top of the run, one option would be to extend the drain uphill to a rodding point, and then encase the part under the extension in concrete. From my days of writing specifications I seem to recall they had to be encased in 150mm of concrete, but that may have changed in these days of plastics piping.
If it is just the pipe that is crossing the area of the extension, then its not to big a deal. The foundations for the extension actually need to bridge the pipe, so as no load is put on them, that involves a lintel over the top to take the block / brick work above, transfering load to foundation at each side but below the pipes.
Maybe worth changing to plastic pipe for run under new floor, to eliminate any possible future problems if they are clay now.
Do you have an access point located where the proposed extension would go as indicated by previous answers?
<span style='font-size:8pt;line-height:100%'>Posted by Tony McC - don't know why the sytem doesn't want to recognise me, but it's bloody annoying!</span>
Assuming this is a 100mm dia pipe, and no deeper than 1500mm, then reckon on 150 quid per metre to replace it with 110mm uPVC or 100mm clayware encased in concrete, with a minimum cost of around 1800 quid, plus yer VAT, guv!
If you have to get into bridging the sewer, as described by Leighton (Ability), you could add another 500 quid.
If you are at the head of the run, and depending on the fittings involved and the actual layout, it could be a lot cheaper to divert the sewer to run outside the line of the proposed extension. This eliminates the cost of concreting in the new pipe, the cost of bridging one, possibly two, walls, and could simplify the drainage requirements of the planned extension.
Your architect should be able to advise (stop laughing! They should, really!!) on the best plan, but you have to bear in mind that architects live on a different plane to us mere mortals.
Unfortunately we would have to create a new access point, and £1800 (+ £500) seems steep, so, as we are at the head of the run, maybe diverting the sewer might be the best option for us.
At least I now know that the problem is solvable, even though it will add (yet more) cost to the extension - and we initially thought it would be cheap and simple ...
