How do I Know the Depth of My Neighbour’s Foundations?

by The Party Wall Surveyor

Question

I have a semi-detached bungalow and want to build a single storey extension adjacent to an existing extension that my neighbour already has.  I have no way of knowing the depth of my neighbours foundations, so won’t know if I need to go lower than his foundations to meet current building regulation requirements, that would then require me to serve an adjacent excavation notice!

How can I progress with my extension as I would need to demolish my current conservatory to do an exploratory excavation to discover the depth of the adjoining extension foundation?

Answer

Being two halves of a semi it is a safe assumption that both yours and your neighbour’s properties have the same depth of foundation. You could therefore dig a trial pit adjacent to another part of the exterior of your property to establish the depth. Too simple?

Follow-up

Can you clarify that if I find the depth of my neighbours foundation Is deep enough for my building regulations requirement footings would I need to serve the excavation notice?  I was advised that I only need serve the notice if I have to go deeper than his foundations?

Answer

That is correct – if you are not excavating deeper than the base of your neighbour’s existing foundations the work does not come within the scope of the Act and there is no requirement to serve notice.