When building a side extension can end in disaster. Stephen Cornish explains Hit and Miss foundations
If you are proposing to excavate a trench to lay foundations for your extension or new drains on your land, the removal of the subsoil could cause structural damage to a neighbouring house, garage, outbuilding and boundary wall. Just see the photo above. Although the excavation is on your land, the removal of subsoil will also remove the support to nearby neighbouring foundations.
The neighbour has a legal right of support through a proprietary right call an easement. These practical and legal issues are recognised in the Party Wall etc. Act 1996 (‘the Act’).
The Act requires a detailed notice, including appropriate drawings, is served on the neighbours if the excavations are (a) within 3 metres of and (b) to a depth which is likely to be below their foundations.
Although the Act prohibits the permanent interference with an easement, the serving of a valid notice permits a temporary interference during the excavation; it is during this stage of the work, however, that damage to a shallow founded neighbouring structure can occur.
The Act requires that the notice states whether it is your intention to safeguard, strengthen or underpin the neighbour’s foundations. Underpinning is the last resort and one acceptable method of safeguarding the neighbouring foundations is to excavate in a ‘hit-and-miss’ sequence.
This involves the foundations being excavated in bays, usually not exceeding one metre in length; bays being excavated at the same time must not be adjacent to each other. This means that at no point is the removal of support to the neighbour’s foundation greater than a metre in length or in more than one place.