Drainage help needed - House extension

[GEO-PAR]

Hi guys, 

 

Helping my brother build an extension down the side and out the back of his house.  We've done a big chunk of the digging but now at the drainage and are a little stuck on how to go about it, where we need manholes, rodding points and so on.  

 

Here's a photo of what the site is currently looking like.  When comparing to the existing plan below, I'm stood above the living room looking down. The metal cover at the bottom of the image is not a manhole - We located the pipe and put this over the top to stop any dirt or stones from falling down in the hole. 

 

 

This is the existing situation.  An existing drainage pipe runs parallel along the back of the house and connects to the manhole as indicated. This drainage pipe is for next door's rainwater (and potentially foul but we're not 100 percent sure).  The houses are circa 1940's (Bath, Somerset) so it appears to be a combined sewer? 

 

 

This is something along the lines of what I am thinking.  So we don't have a drainage pipe running below the house, we re-route it to run around the outside of the extension.  Does this look sensible or is it better to just leave as is and build over it?   I'm thinking all the new drainage pipework goes to the back of the house as shown. 

 

 

In terms of foundations, we're going down the approach of beam and block as the existing house is suspended timber ground floor (and therefore need to preserve air flow). I believe we need a min of 400mm between the pipe and the house, although ideally we'd be able to get this closer and use the same trench as the footings. 

 

 

Any help is massively appreciated! 

 

[kandgmitchell]

Presumably you have a "build over agreement" for that sewer? That will dictate the construction arrangements required.  If you do divert then don't forget you are increasing the length of drain between two fixed points and thus the gradient must be lower - perhaps too low. You will need access at each of those bends, both of which seem to be in the neighbour's garden - are they ok with that? You will also need to check with the sewerage provider with respect to diversion.

[GEO-PAR]

Okay cheers - Sound like the easiest thing to do is leave in situ and apply for a build over notice, and just have it run below the extension in the current position? 

 

[kandgmitchell]

Go on the "developer" bit of your sewerage company (Wessex Water?) and look for build over agreements. Most now have a "self certify" system where if you meet all their criteria they'll agree a build over (for a fee) and give you the detail you have to use where actually building over the sewer. It'll be easier than diverting.

[GEO-PAR]

okay will do - thanks