Using Party Walls
If you plan to use a neighbour's side wall to support the building of an extension on your own property, first check where the boundary is. If the wall belongs entirely to your neighbour, you have no right to use it as a support. If your neighbour is sympathetic and allows you to use their wall, arrange for your solicitor to draw up a legal agreement, or there may be problems when one of you comes to sell. If the property line runs through the wall, it is a party wall - you have the right to use it as a support providing it complies with building regulations. Your neighbour has the right to consult a surveyor, at your expense, to ensure that your building work will not damage their interests.
Building Near a Boundary
If you wish to build within 3 m (10 ft) of your neighbour's building and lay foundations deeper than those of your neighbour, the law requires you to serve a notice on them. Your architect or surveyor will act for you on this. If the neighbour agrees, work can proceed. Otherwise, both parties must appoint a surveyor or surveyors to sort out their differences.
