Many builds will have to make a party-wall agreement with their neighbours if your building works affect an adjoining property. The conditions for undertaking any work of this nature are governed by law in the Party Wall etc. Act 1996. The agreements endeavour to ensure each property is maintained and is of equal or better structural integrity than of that presently in place.
A9 Architecture will always advise you when you need to instruct a party-wall surveyor or expert to protect both you and your neighbour’s properties from potential failure in the future.