How much do side return extension drawings cost in London?

What the starting price covers

A side return is the strip of ground beside the rear projection of a Victorian terrace. Filling it makes the kitchen wider, and the drawings have to resolve a tight site. Our fee, from £905 inc survey, includes a measured survey of the house, the passage and the neighbour's flank wall, then the plans, elevations and sections of the infill and any wider rear extension.

We also give you a written verdict: permitted development or a planning application. A second technologist reads the drawings before they go, and any change the council requests is redrawn free until it approves.

Permitted development and its limits

A single-storey side extension built under permitted development must be no more than 4 metres high and no wider than half the original house, with eaves of up to 3 metres where any part is within 2 metres of the boundary. Outside materials must look similar to the existing house.

Some side returns are in conservation areas, and there side extensions are not permitted development. In those, you apply, and the officer reads the design against the street. The council's fee is £548 from 1 April 2026.

The boundary: your neighbour's wall

A side return infill is built against, or on, a boundary. Building a new wall on the line of junction needs a month's notice, and cutting into a party structure or fitting steel into it needs two months. We draft the notices as part of the work.

Do not leave this to your builder to raise on the day. Notices served late hold up the programme.

Warm, bright and compliant

A side return is mostly glass, and glass is what building regulations watch. A new element in an existing home must meet a wall U-value of 0.18 W/m²K, and the rooflights you want over the infill count towards the glazing allowance. We note both on the drawings, and our SAP calculations can trade glazing against insulation.

See the full range on our side return extension drawings page, and the wider options in the rear extension guide.

Getting a fixed quote

Send the address and a photograph of the passage. We tell you in writing which route applies and what it will cost.

The figures, with sources

1. 4 m

   Tallest a single-storey side extension may be as permitted development, at no more than half the house width.

   Source: General Permitted Development Order 2015, Schedule 2, Part 1, Class A.1(j), checked 15 Oct 2026

2. None

   Side extensions are not permitted development on conservation area land.

   Source: General Permitted Development Order 2015, Schedule 2, Part 1, Class A.2, checked 15 Oct 2026

3. 3 m

   Greatest eaves height where any part of the extension lies within 2 m of the boundary.

   Source: General Permitted Development Order 2015, Schedule 2, Part 1, Class A.1(i), checked 15 Oct 2026

4. 1 month

   Notice needed before building a new wall on the line of junction between two properties.

   Source: Party Wall etc. Act 1996, section 1, checked 15 Oct 2026

5. 2 months

   Notice needed before cutting into a party structure or inserting steel in it.

   Source: Party Wall etc. Act 1996, section 3, checked 15 Oct 2026

6. £548

   Council fee for a householder application to extend one house from 1 April 2026.

   Source: Ribble Valley Borough Council, national fee table from 1 April 2026, checked 17 Oct 2026

7. 0.18 W/m²K

   Limiting wall U-value for a new element in an existing home.

   Source: Approved Document L Volume 1, Table 4.2, checked 15 Oct 2026

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