How Much Does a Loft Conversion Cost in London? (2026 Price Guide)

A loft conversion in London typically costs between £22,500 and £55,000 depending on the type, size and finish. The single biggest factor isn't the size of your loft — it's which of the four main conversion types your roof can support.

Price by conversion type

Here's what each type actually costs for a typical London terrace or semi, including structural work, insulation, a staircase, electrics, plastering and decoration:

A Velux conversion is the cheapest because it doesn't alter your roof's shape — you're just adding roof lights, flooring, insulation and a staircase within the existing structure. A mansard is the most expensive because it rebuilds most of the rear roof slope to near-vertical, maximising headroom but requiring significantly more structural work.

What actually drives the price up or down

Head height

You need roughly 2.2m from floor to ridge for the space to count as usable. If your loft has less than this, you may need to lower the ceiling below (expensive and disruptive) or the project may not be viable at all. This is the first thing we check on a free site visit.

En-suite or no en-suite

Adding a bathroom typically adds £6,000–£10,000 on top of the base conversion price, covering plumbing runs, waterproofing, tiling, and sanitaryware.

Roof structure

Older trussed roofs (common in 1960s–80s builds) usually need more structural steel to open up the space than traditional cut-roof construction found in Victorian and Edwardian houses.

What's included in a fixed-price loft conversion quote?

A proper quote should cover structural steelwork and joists, insulation to current building regulations, a new staircase, full electrics and lighting, plastering and decoration throughout, and if applicable, waterproofing and fit-out for an en-suite. If a quote looks unusually low, ask specifically what's excluded — staircases, electrics, and decoration are common items that get left out of cheap quotes and added back as "extras" later.

Do you need planning permission?

Most loft conversions in London fall under Permitted Development rights, meaning no planning application is needed. The main exceptions are mansard conversions (which usually do need permission), listed buildings, and some conservation areas. We check this for free at the site visit before you commit to anything.

How to get an accurate price for your specific loft

Price guides like this one give you a realistic ballpark, but the only way to get an exact figure is a site visit — head height, roof type, and access all affect the final number. See our full loft conversion service or use our instant cost calculator for a rough estimate based on your square meterage.