Moving stormwater drain in lightwell

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Hi,
i am currently having a my basement converted and we have just discovered a stormwater 6" clay pipe at the front, 1.5m from the property around 1.6m deep. This is right in the middle where the proposed lightwell is to be situated.

Thames Water have asked for the pipe to be diverted around the outside of the lightwell and that there needs to be manholes at every turn(4 in total) and rodding access. The builder has advised that this would be very costly. Besides there are gas/water services in both the pathway and front area so it would be very difficult to build the manholes.

Has anyone any experience to share? The best solution would be to have the pipe diverted internally around the walls of the lightwell and am not convinced by the information received thus far from TW - their solution appears extreme for a stormwater pipe.
BCO says its ok to simply divert the pipe internally but as the pipe belongs to TW but they would have to approve the diversion. i also have to pay a fee of around£550!

Any advice?
Thanks
 
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Whichever way the pipe is diverted it will still need to achieve a suitable fall, making too long a diversion may compromise the fall, which in itself can cause a problem.

Ultimately the pipe is the responsibility of Thames, it's their call. As there responsibility they need to ensure the integrity of the pipe and maintain access to it should the need arise. Putting it inside a private property could present Thames with issues, should the pipe leak then the question of liability arises for damage caused by any such leak, access for inspection and/or maintenance etc. Whilst the BCO may not have an issue so far as Building regs are concerned, to divert a public sewer internally is highly irregular! The external diversion, with a manhole at every change in direction is standard practice in these circumstances.

Ultimately it may be a storm drain, but as with any drain there is always the potential for problems, Thames I think are merely protecting their own interests as would any statutory undertaker when work affecting their assets is proposed. The logistics of achieving their requirements in order to achieve yours are simply your problem i'm afraid. The fee is standard practice, covers Thames costs for ensuring the work is done to their satisfaction, and thus preserving the integrity of the sewer. Bodged sewer work can soon lead to a lot of problems, which in themselves are not cheap to remedy, and that's before any costs are settled for resulting damage to properties or fines imposed after prosecution for pollution incidents!
 
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I'm with Hugh on this one, in that it sounds impractical as well as potentially troublesome to create such a convoluted diversion. It will create havoc with falls and flow and (as said) mean zero fall.

Sounds like your light-well plans are scuppered. Have you consulted the designer or architect?
 
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Hi Hugh, many thanks for your comments which clarifies the situation.

The water company have already offered a solution: 3 manholes and the pipe coming back into the lightwell for the final turn so that there is no need to encroach on the neighbours land.

I do actually live on a hill (not steep but quite a gradient) so the issue of a fall is less of an issue than it might have otherwise been, - the advantage of the pipe going internally is that the diversion has less distance than TW's solution.

A pump is not practical as a long term solution.

I am not optimistic and think the lightwell will have to be smaller in size :(
 
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Hi Hugh, many thanks for your comments which clarifies the situation.

The water company have already offered a solution: 3 manholes and the pipe coming back into the lightwell for the final turn so that there is no need to encroach on the neighbours land.

I do actually live on a hill (not steep but quite a gradient) so the issue of a fall is less of an issue than it might have otherwise been, - the advantage of the pipe going internally is that the diversion has less distance than TW's solution.

A pump is not practical as a long term solution.

I am not optimistic and think the lightwell will have to be smaller in size :(


Going off at a tangent, apparently they got two massive water pumps in the Severn tunnel working 24/7 to keep the water level down.
 
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Hi,
i am currently having a my basement converted and we have just discovered a stormwater 6" clay pipe at the front, 1.5m from the property around 1.6m deep. This is right in the middle where the proposed lightwell is to be situated.

Any advice?
Thanks
Could the lightwell not be sloped.... /o ....over the drain :idea:
 
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Does beg the question if the area you are extending the lightwell into is actually your to use, or public footpath?
 
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Yes the lightwell will have to be stepped if the pipe cannot be diverted internally.

Perhaps i am just unfortunate as i do see many large lightwells and guess the storm pipe for these basement flats are in the street or that they have large front gardens and the pipe is quite away from the properties. My front garden is 4.8m and the pipe around 1.2m.
 
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Too steep a gradient can be as much of an issue as too shallow a gradient. Problem can then arise with the water flowing into your first chamber at a rapid rate of knots, not only does it have to make the turn to go out again, but is then also being fed into a pipe on a shallower fall which may slow the flow down.... This can then lead to the chamber surcharging and the water making its exit out the cover......

Believe me, I have seen occasions where as a result of heavy rainfall, the volume of water entering a chamber being unable to exit fast enough, rises until it eventually blows the lid off! Not always lightweight lids either, on one occasion the lid, frame and several square metres of surrounding block paving was blown clear of the manhole. (These covers are cast or ductile iron, and require a two person lift due to their weight!) :eek:
 
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Too steep a gradient can be as much of an issue as too shallow a gradient. Problem can then arise with the water flowing into your first chamber at a rapid rate of knots, not only does it have to make the turn to go out again, but is then also being fed into a pipe on a shallower fall which may slow the flow down.... This can then lead to the chamber surcharging and the water making its exit out the cover......

Believe me, I have seen occasions where as a result of heavy rainfall, the volume of water entering a chamber being unable to exit fast enough, rises until it eventually blows the lid off! Not always lightweight lids either, on one occasion the lid, frame and several square metres of surrounding block paving was blown clear of the manhole. (These covers are cast or ductile iron, and require a two person lift due to their weight!) :eek:
Moving water has enormous force.
 
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Yes the lightwell will have to be stepped if the pipe cannot be diverted internally.

Perhaps i am just unfortunate as i do see many large lightwells and guess the storm pipe for these basement flats are in the street or that they have large front gardens and the pipe is quite away from the properties. My front garden is 4.8m and the pipe around 1.2m.
OK step it and then cover the sides with polished stainless steel sheet - that`ll bounce some light around ;)
 
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