build over foul sewer

10 Nov 2010
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United Kingdom

We are in the process of getting some plans drawn up for a 2.5 x 3m extension for the front of our house with a pitched roof. Unfortunately there is a foul sewer running along the front of our property (shallow, 100mm pipe) and this is adopted by Severn Trent Water (STW). Hence we are going through the process of applying to build over with STW.

The guy we have used to draw up the plans suggested that we replace the existing pipework and put a manhole either side of the build which seems fine. When he drew it for the STW application he put a bend in the foul sewer under the build because there is currently a manhole and a bend in that location. STW have rejected this and asked for the pipe to be straight under the build and then bend at the manhole cover outside the build.

Am I wrong in thinking that the architectural consultant should have known that putting a bend in the sewer pipe under the build would be a bad idea and rejected. He wants to charge us £200 to redraw the plans with a straight pipe for resubmission to STW which seems excessive.

I'm going to phone him this afternoon so any thoughts from more experienced people greatly appreciated.

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Normally you would try to avoid having any bends beneath a build if possible. In underground drainage generally it is standard practice to have a manhole on every change in direction unless it is a gentle curve or one cannot be installed for some reason. Whenever you submit drawings to the utilities there is a given acceptance that they may wish to amend the proposals upon review. However it should be clear in his fee quotation whether he has done this at a fixed price or hourly or what. £200 does sound cheeky but is there a lot of work involved? What’s his hourly rate? Having been stung in the past by the utilities myself I now state on my fee quotations that any liaison with the utilities, if it’s included within my remit, is on an hourly basis. Before you challenge the price ask for a full breakdown of the price assigning time/money to each item being charged for.
Am I wrong in thinking that the architectural consultant should have known that putting a bend in the sewer pipe under the build would be a bad idea and rejected.

No, you are correct in thinking that

Bends = blockage points and need access. And you certainly don't put bends under buildings

Roll the plans up and hit the consultant with them - edge on as it hurts more
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Usage of the drain will determine the risk of it blocking - one connection from a kitchen sink is less likely to block than a run of the whole terrace

Also, a bend could be installed and a rodding point extended to outside the footprint, but in the OP's

Alternatives could be sorted out on site, but in the OP's case it is purely bad design, and he should not have to pay again for what should have been done in the first place

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