Many single-storey rear extensions fall under permitted development rights and do not need planning permission — provided they meet size, height, and boundary distance rules. Two-storey extensions, side extensions, and anything in a conservation area or AONB almost always need planning approval. Your architect will confirm what applies. RW Groundworks does not handle planning applications, but we can start as soon as you have approval.

Building regulations require a minimum foundation depth of 1 metre in most cases, but the actual depth depends on ground conditions. Clay soils need deeper foundations (sometimes 1.5m+) to get below the zone affected by seasonal moisture changes. Near trees, depths can increase to 2m or more. In Cornwall, rocky ground sometimes allows shallower foundations if the engineer confirms adequate bearing. The structural engineer specifies the depth — we dig to it.

If your extension foundations are within 3 metres of a neighbouring property (or 6 metres if you are digging deeper than their foundations), you need a party wall agreement under the Party Wall Act 1996. This involves serving notice on your neighbour and, if they do not consent in writing, appointing a party wall surveyor. This is a legal requirement — starting work without it can result in an injunction. Your architect or a party wall surveyor handles this before we start on site.

Strip foundations use less concrete — you pour a concrete strip (typically 225mm deep) at the bottom of the trench, then build block walls up to ground level. Trench fill uses more concrete — you fill the trench almost to the top with concrete, which is faster because you skip the below-ground blockwork. Trench fill is common in Cornwall where deep foundations are needed because it reduces the time operatives spend working in deep trenches. The structural engineer decides which type suits the site.