Jml Posted September 18, 2017 Share Posted September 18, 2017 (edited) Not sure, this question is in the correct section. We were hoping to do our extension on a building notice, but since we have a sewer running under our house and proposed extension we have to get building regulations approval. Having gone through the regulations most seem fairly straightforward once we have appointed structural engineers, apart from drainage, part H, which has me totally confused. We have a 1950's bungalow which has been extended in all directions by previous owners, including a part length rear extension which has a sewer running under it serving at least three properties. This extension was built prior to adoption of shared sewers by the water companies, in this case Thames Water. Our planning permission extends this rear extension to the full length of the house, so we will be building further over the sewer, for which we need prior approval by Thames Water. At present there are two manholes in our garden, one on entering the garden, the other under the proposed extension which will have to be moved or removed. If we move the manhole in line with the sewer, there is only a gap of c. 97 cm between the house and the garage where it can go. Do we need this second manhole? Can we build it in such a small gap? We may be better to divert the sewer from under the house around the garden is this easy/ possible and how many manholes would we need? Any suggestions/ advice would be much appreciated. existing plan.PDF proposed plan.PDF proposed site plan.PDF Edited September 18, 2017 by Jml plans added Link to comment Share on other sites More sharing options...
ProDave Posted September 18, 2017 Share Posted September 18, 2017 Is it just an inspection chamber for rodding, or is there a branch at this location? (take the lid off and rake a picture?) Link to comment Share on other sites More sharing options...
Jml Posted September 18, 2017 Author Share Posted September 18, 2017 Manhole has four pipes joing main flow here, basically serving our bathroom and kitchen at present. At present we have kept the bathroom where it is in new design, but I dont know if we can keep the connection to the mains here or not. Link to comment Share on other sites More sharing options...
PeterW Posted September 20, 2017 Share Posted September 20, 2017 Sorry I'm late to this one @Jml You can build over that but Thames will have a specification about building over that you have to follow. Severn Trent for example insist on either you replace all the pipework under the slab with uPVC and have a post build camera inspection or you have a camera before and after but retain the clay pipe. If you self certify the build over then they have some pretty strict rules that you need to follow - internal sealed manholes for example aren't allowed - and there have to be certain distances from boundaries. Thames produce this guide which I assume you've already read ..?? https://www.thameswater.co.uk/-/media/Site-Content/Developer-Services/Guidance-for-building-over-a-sewer.ashx?la=en&la=en You don't need a manhole at all on the run but I would make provision for rodding at least one or two points on the run - you can do this with dead legs and rodding eyes quite easily. Link to comment Share on other sites More sharing options...
Jml Posted September 21, 2017 Author Share Posted September 21, 2017 Many thanks for your response and the link. I have read Thames Water build over guide and unfortunately as we are building over a sewer manhole, as shown in the picture above, we will need an agreement from them and are unable to self certify. What has me confused is that we will have to make at least one if not two connections to the sewer we are building over, one for the bathroom/utility room and another for the new kitchen. The former could use the connections as shown in the manhole, but would we be allowed to connect to the sewer with a rodding eye or dead leg rather than a manhole at that point? Link to comment Share on other sites More sharing options...
PeterW Posted September 21, 2017 Share Posted September 21, 2017 You should connect with a Y branch at 45 degrees to the flow - you've got one manhole at the top end of the run, a second isn't needed. Replacing that manhole will require careful planning - every connection will need to be ready to go and you need to have dug down past invert level before you block the top side flow with a plug and then work very quickly as you will be stopping a lot of flow from 4 houses...!! I'd even failsafe the plugs with one on both sides of the manhole just in case ..... Link to comment Share on other sites More sharing options...
Jml Posted September 21, 2017 Author Share Posted September 21, 2017 Many thanks, great news that we don't need the manhole!!! But, I think I'll leave removing it to someone who knows what they are doing, otherwise could get very messy! This means I can now try and design our drainage system, probably means lost more questions under the drainage section though. Link to comment Share on other sites More sharing options...
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