House Extensions in London

A side return fills the narrow strip of outside space that runs alongside the back of a Victorian or Edwardian terrace. It is rarely large in square metres, but because it widens a kitchen across the full span of the house, it usually changes how the ground floor works more than its size suggests.

A rear extension pushes the back of the property further into the garden. It is the simplest form structurally and the easiest to get right, provided the new roof, drainage and glazing are properly resolved.

A wrap-around combines both, which brings a more demanding structural picture: longer spans, more steel, and a roof geometry that has to drain cleanly at every junction.

A loft conversion adds space without touching the footprint. Head height is the deciding factor — measured from the top of the ceiling joist to the underside of the ridge — and no amount of design work can create it if it is not there.

The cost of an extension is rarely driven by floor area alone. Steel spans, foundation depth, drainage diversions and the extent of glazing move a budget far more than the extra square metres do. A large opening with a slim-framed sliding door costs a multiple of the same opening with standard French doors, and the steel above it has to be sized for the load either way.

Roof lanterns and rooflights are usually the difference between an extension that feels like part of the house and one that feels like a corridor with a table in it. Daylight from above reaches deeper into the plan than daylight from a wall, which matters most in exactly the situation extensions create — a long, deep ground floor.

Many single-storey rear extensions fall under permitted development, but permitted development is a set of limits, not a guarantee — depth, height, materials and boundary position all have thresholds. Conservation areas, listed buildings and flats sit outside it entirely.

Where an extension is built up to or across a shared boundary, or involves excavation near a neighbouring foundation, the Party Wall etc. Act 1996 applies and notice must be served on the affected neighbours. This is a legal process with its own timescales, and it is worth starting early — it is one of the most common causes of a delayed start on site.