Narthecius

Thanks @Mr Punter. The bottom 3 properties on my drawing have extended. Apparently 1 has a raft, 1 has traditional footings and 1 has piles, which isn’t very helpful 😂. Good idea re. Building Control - I will get in touch.

I am hoping to build a small (5.5mx4m) single-storey rear extension on the back of our 1930's end-of-terrace property. Prior to getting planning/building regs drawings approved, I want to confirm the feasibility of the project and approximate cost of the foundation system before I proceed. Soil surveys I was given when I bought the property indicate the ground conditions are poor (made-up ground) and it's possible a pile or raft system is needed. There is an adopted sewer (invert level 1m and all pipes <160mm) that converges in the alley next to my property. As far as I understand, building over pipes is relatively simple when using traditional footings, but more complicated with pile/raft systems. Having read through Thames Water's build over guide, piled foundations must be 1.5m from the sewer. I have attached a (guessed & not to scale) drawing of the sewer system. Does anyone have a recommendation on how to proceed from here? CCTV drain survey? Engage a structural engineer? Ask Thames Water? Many thanks!

Thanks @markc, that's definitely the way I'm leaning. Is there a recommended gap between the properties? I guess as long as it's big enough to get someone down there for access & prevent damp that's sufficient?

We are planning to build a single storey extension to the rear of our property, hopefully around 4m out and 3m high. Our house is a 1930s end-of-terrace. Our attached neighbour's house has a half-width extension (constucted 20-30 years ago) built right up to the boundary of our property, extending approx. 3.7m out and 2.5m high. I've been told that it would be best to seek a party wall agreement and build that side of our extension off the existing wall. There are reasons why I'm hesistant, but I understand leaving a gap between the properties isn't ideal either. If we wanted to build completely separately, is there a recommended gap between the buildings? Concerns: Our garden boundaries are not straight out from the house, instead they are a parallelogram, sloped in towards my garden. Because our neighbour's extension has been build straight off their house, this has left a small triangle of their land on our side of the fence. I imagine if I wanted to build on this land it might be complicated? We would want to build up to maximum 3m height - could this be done off the existing wall? If the neighbour wanted to knock down and redevelop their existing extension I guess this could be complicated.

Thanks Jilly. I believe I will need to follow the "Prior Approval" permitted development route, because I'd like to go out 4m. I will start with getting the drawings done!

Can move this elsewhere if it's better DYNAMIC PROBING REDACTED.pdf SOIL SAMPLE REDACTED.pdf

Hi all, Thought I'd come to introduce myself. The project I'm doing isn't very exciting compare to some of the builds on here, but I'm very much looking forward to contributing to the community if I can (and probably asking for lots of help too!). I'm in London and looking to do a smallish (20sqm) rear extension on my 1930's end-of-terrace house. I had a contractor quote for the build and we are in different worlds. Budget is ~£75k, but quote came in 130k all in, hence going down the self-managed build route. I am a competent DIYer and am able to dedicate some time to planning/helping, although I doubt I would be able/want to tackle the big stuff. The property had planning permission in 2007 for a rear extension and I inherited all of the documentation for this when I bought the property. At that time the soil was surveyed and it was discovered that it was "made up" ground. Pile and raft foundations were recommended. My first question - would the soil survey from 2007 still be useful? I'm guessing not much would have changed underneath the ground in the 16 years since the survey, although I could easily believe that piling technology has moved on. I can post the soil surveys (borehole & dynamic probing) here - is there a good place on the forum for things like this? Thank you all.