Trench foundation at boundary? Cavity wall position

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Tyrone Thompson

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I’m building a rear extension on my end of terrace bungalow, my Architect has specified a 600mm x 1000mm concrete foundation. At the adjoining boundary to next door we have a concrete post fence, the 150mm “toe” of foundation on that side of the 300mm cavity wall will need to go slightly past the centre of the existing fence.

I was thinking that I could leave the fence in place, dig right up to it and have my cavity wall sit off centre on the foundation? But I presume that a BCO would not allow this as the weight is not spanning equally along the width of the foundation.

has anyone had experience with this sort of situation? And what a BCO would allow? I have all party wall details sorted on this, just saying.

I think that it could be more suitable if I were to get the engineer to design an offset foundation for that side (at the boundary)
 
An "observation??"

If the dimensions were known why did the designers leave you in this position??

Ken
 
I don’t know why my architect hasn’t raised this issue since he’s done the survey, have you had this situation before?
 
Do you know exactly where the "Boundary" is?

At times it has nothing to do with the fence line, not often but can happen??
 
The boundary is centre of the fence line, a trench foundation would end up under the fence by 50mm, any experience with having the cavity wall of centre on the foundation?
 
Would your neighbour let you take the fence down then start it from the corner of your extension once its built to that height?
 
You are allowed to build right up to the boundary line and project your footings beyond it but must serve the required notices. In this case it will be a ‘Line of Junction Notice’ under sections 1 (5) & (6) of http://www.legislation.gov.uk/ukpga/1996/40/section/1.

If he were to build a similar extension in the future he would have the right to cut off the part of your foundations that project – subject to serving the required notice.
 
Yes we had exactly this and the structural engineer said no problem building right on the edge of the foundation as it's only domestic. We were having trench fill 1m deep.
It looked like the fence was entirely on the neighbour's side even though it's apparently our fence so the builders didn't touch it but the outer edge of the outer leaf is on the boundary line.
 
Tyrone Thompson said:
Thanks for the response, did the buildings control officer saying anything about it?
Click to expand...
No but they had no way to know, unless they measured and took photos and somehow cottoned on to the fact that the wall was closer to the edge. They just assumed it was built to the approved plans on the whole.
Most things the building control people wouldn't know, they came to inspect at dpc level and again after the roof was on, so there's a lot that could be hidden in that time.
 
I suppose if you think about things, the BCO is faced with an Architects plan, Structural Engineers designs and drawings, if the BCO arrives at DPC stage there is no way at all given [it appears] that you are building next to a field or something like??? not to a neighbour who is watching every single move? [or are they>] then without setting up a "total station" with highly accurate GPS the BCO will not be able to clock a 50.mm [shall I call it] discrepancy ? of sorts??

Having said that the advice given above as regards ‘Line of Junction Notice’ from Motorbiking above should assist.

Ken
 
Yeah, I think it was more the fear that they may notice the dimensions of the foundation dug where it meets the existing house, as they wouldn’t match up accurately to the cavity wall position.

maybe too the “toe” of the foundation showing 300mm instead of 150mm.

maybe I’m just looking into it too much
 
Oddly, Architects don't always understand the Party wall rules, when my Mrs commissioned plans, her architect advised there were no party wall notices needed as we weren't building on the boundary. I knew our existing house's foundations were very shallow and it would be reasonable to assume our neighbours would be the same, therefore we severed notice under the 3M rule as we were likely to be digging below the neighbours foundations.
 
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