Proposed Extension – Foundation Depth and the Need to Serve Notice

by: The Party Wall Surveyor


We have planning permission to extend our garage to the front and side of our property. The single storey side extension will be approximately one metre wide, within our boundary but approx 1.2 metres from our neighbour’s house.  Both houses are part of an estate built in 1983 and both are piled, as will be the new extension.

We are aware of the Party Wall Act, but do not think it applies as the new foundations should not be deeper than ours since both houses were built by the same builder at the same time.  How can we prove this? We do not think that our neighbour will allow us access to his deeds as he has already objected to our plans. Can he insist on invoking the Party Wall Act if he refuses to allow us to ascertain the depth of his foundations.


If you are confident that the foundations to your new extension will not be deeper than those to your existing house, and by extrapolation than those of your neighbour’s property, then there is no requirement for notice. 

I would recommend that you write to your neighbour explaining your thinking and add that in the absence of any information to the contrary you do not intend to serve notice. Only you can invoke the Party Wall Act by serving notice, the only option open to your neighbour once work commences would be to obtain an injunction but that would require some evidence – the court would not be impressed if any such evidence had not been provided to you when requested.


We did as you suggested and also checked original building records to find that the structural engineers / surveyors had specified that both houses were to be piled to a depth of 5/6 metres minimum. (I might add that a small extension has since been added across the back of our neighbour’s house.  This was built on a raft, but is just over 3 metres in a diagonal line from the line of our extension ).

Our neighbour replied to our letter, but not with any useful information.  They asked us to notify the depth of our new foundations and stated that if we did not invoke the Party Wall act we would not have any right of access for repairs etc. (This also means that our side wall would have to built from inside).  They also stated that without the Party Wall Act any damage to their house could be put down to our building works and it would be up to us to prove otherwise.
At the suggestion of our builder we have since employed a company to do a 10 metre borehole analysis of the soil and the report shows no problems.

We fully intend to build our extension and would issue a Party Wall Notice just to make things easier and avoid any future claims on us, our builder or any damage to his reputation, but we are worried that our neighbours will make this as expensive as they possibly can. Either way they will try to cause delay.  We have just been told that work is will start on 01 October so time is short.


If you have established that the work does not come within the scope of the Act any notice issued would be invalid. Assuming that your neighbour will dissent to any notice served and appoint a surveyor, that surveyor (and your appointed surveyor) will have a duty to point out that the notice is invalid.

When your neighbour says that ‘without the Party Wall Act any damage to their house could be put down to our building works and it would be up to us to prove otherwise’ they may be refer to a famous case which you can read about here.

The difference with the case is that the works did come within the scope of the Act. In this situation it would be for your neighbour to prove a link.

Perhaps an acceptable compromise would be for you to pay for a Schedule of Condition to be prepared by a local surveyor (jointly chosen) and for you both to keep a copy on file.