How much do double-storey extension drawings cost in London?

Why two storeys cost more to draw than one

A single-storey extension has one floor plan and a roof you can read at a glance. A double-storey one has two floor plans that must stack, a first-floor window wall that a neighbour will look at, and a roof that has to join the old one without a leak. Each of those is a sheet the officer will check.

Our fee for it is £755 drawings + £150 survey (£905 total). It includes the measured survey, the existing and proposed plans, elevations and sections, the roof junction and the forms.

The two numbers that decide the route

That second figure catches short gardens.

Permitted development stops being generous the moment you add a floor. Class A lets an extension of more than one storey go no more than 3 metres past the rear wall. It also bars one that would be within 7 metres of any boundary opposite the rear wall.

That second figure catches short gardens. With a 3-metre extension, the garden must run at least 10 metres from the rear wall to the end boundary, and many small London gardens are shorter. If the extension fails either number, the route is a planning application, and the fee for one house is £548.

Rules that shape the drawing even when you are inside the limits

Even a compliant design carries conditions. The roof pitch of the new part must, so far as practicable, match the pitch of the original house. Any window in an upper-floor side wall must be obscure-glazed and non-opening unless its opening part is more than 1.7 metres above the floor.

An extension within 2 metres of a boundary may not have eaves higher than 3 metres, and it may not be wider than half the original house if it extends past a side wall. We set these out on the elevations so you see them before the builder does.

Conservation areas, which are article 2(3) land, bar any rear extension of more than one storey altogether.

How long the council takes, and what comes after

For an application that is not major development, the council has 8 weeks from the day after it receives a valid one. Nationally, 93% of householder applications in the year to June 2026 were decided in that time or an agreed one.

After permission come building regulations drawings, the structural engineer’s calculations at £389, and often a party wall notice. If a neighbour’s window has had light for twenty years, a tall wall beside it can raise a right-to-light claim, which is a civil matter outside planning.

The levy you probably do not pay

Community Infrastructure Levy is a charge on new floor space. The GOV.UK guidance says residential extensions under 100 square metres that do not create a new dwelling are exempt, so a normal family extension is not charged.