How much do loft conversion drawings cost in London?

The bills around a London loft, in the order you meet them

Think of a loft conversion as four small bills rather than one. The first is ours: £475 drawings + £150 survey (£625 total). That covers the measured survey of your house, the planning-ready drawings and a fixed fee that does not move once agreed.

The second is the council’s, and it may be zero. Under permitted development many lofts can go ahead without an application. If yours cannot, the fee for altering one house is £548 from 1 April 2026.

The third and fourth are building control, whose fee is set by the body you appoint, and the structural calculations that size the steel. Ours are £389. Neither of those two is in the drawing fee, and we say so before you pay anything.

• Our loft drawings and measured survey: £475 drawings + £150 survey (£625 total)
• Council planning fee, only if permission is needed: £548 for one house
• Optional Lawful Development Certificate: half the planning fee, so half of the householder fee
• Structural calculations for the new beams: £389

Does your loft need a planning application?

The roof slope that faces the street decides most London cases.

Often not. Class B of the General Permitted Development Order lets a house owner add to the roof as long as the extra roof space is no more than 40 cubic metres for a terraced house or 50 cubic metres for any other house. Nothing may rise above the highest part of the existing roof, and nothing may extend beyond the roof slope that faces the street.

That last limit decides most London cases. A rear dormer on a terrace can fit inside 40 cubic metres. A dormer on the front slope, or a mansard that rebuilds the whole roof line, falls outside it and needs a planning application.

Conservation areas are the second filter. The same Schedule says the roof right does not apply on article 2(3) land, which includes conservation areas. Islington alone has 42 conservation areas, and it has removed permitted development rights by Article 4 direction in 40 of them.

Why a Lawful Development Certificate is worth the half fee

You do not have to apply for one. A certificate is the council’s written confirmation that the work is lawful, and it is useful evidence when you sell the house later. For a loft the fee is half the planning fee, so half of the £548 householder fee.

The planning guidance also says the council decides only on the facts: planning merits are not relevant. So the drawings must show the volume calculation and every limit, which is exactly what we draw.

What building regulations ask of the drawings

A loft that adds a storey more than 4.5 metres above ground needs a protected escape route down to the front door. Approved Document B asks for fire-resisting doors (E 20) and partitions (REI 30) along that route, upgrading existing doors where needed.

The stair has its own rule. Approved Document K asks for 2 metres of headroom, and for a loft conversion allows 1.9 metres at the centre of the stair falling to 1.8 metres at the edges where there is no room for more.

These are the first rules a cramped loft fails, and the drawings are where you find out, before a builder is on site. Our building regulations drawings are a separate set from the planning one.

The neighbour’s wall

Most London lofts rest steel beams on a party wall. The Party Wall etc. Act 1996 gives a building owner the right to cut into a party structure, and section 3 requires the notice to be served at least two months before the work starts.

That is a timing issue more than a cost, but it belongs in your plan on day one. We prepare party wall notices from the same survey.