Basement Excavation

“We have been completely happy with the service provided and would happily use Act again, in fact, we may well be in touch some time soon!”

– Residential Homeowner, Mr Tomlinson

The Dangers of Basement Excavation –  a thorny party wall act issue

Almost all basement extensions are subject to one or more of the provisions of the Party Wall etc Act 1996.

The provisions cover the following:-

  • Excavations within 3 or 6 m (depending on depth) of any adjoining structure (structures could include patios, hard standing or even a garden shed so beware) – section 6
  • Underpinning to a party wall – section 2 (2) a
  • Placement of reinforced foundations (called ‘special’ foundations) on adjoining owners land, for example as part of the underpinning – this provision is subject to the adjoining owner’s specific consent.

There are a number of potential liabilities that arise for the Building Owner when exercising these provisions. 

  • The building owner must not cause the adjoining owner unnecessary inconvenience by the works. This must be carefully considered and determined by the appointed surveyors and would cover such matters as timing and execution of the works.
  • The building owner must compensate the adjoining owner, for any loss or damage. The adjoining owner only needs to show that the loss claimed resulted from works under the Act, and does not have to prove negligence etc. Section 7(2) not only covers physical damage but also financial loss, rental income, loss of trade, diminution in value of property etc

The design team must also take care that the proposed basement does not restrict the development potential of the adjoining buildings.  

  • The proposed basement design (in particular underpinning to the party wall and construction of adjacent slab) may effectively cap the load on the party wall that its foundations can bear. Eg, this could limit the development potential of the adjoining owner say, for example if he wanted to increase the loads on the party wall with a mansard roof extension.
  • The new basement could also increase the costs of building a basement on the adjoining owner’s side. These additional costs would be classed as a ‘loss’ and potentially claimable by the adjoining owner. This could also affect the value of the adjoining property
  • The design team and the party wall surveyors should carry out an appraisal of the effect a proposed basement will have on the development potential next door, to mitigate any potential claims arising in the future.

In summary, retro-fit basements need to be approached with caution as there are many potential issues to be considered.

If you require any further information, please do not hesitate to contact us here or call us on 0845 077 9559.