How much does a London
loft conversion cost?
2026 prices, by type.

Typical 2026 London ranges (inc. design, build, contingency & VAT): Velux conversions £45k–£75k; rear dormers £75k–£120k; L-shape dormers £95k–£150k; hip-to-gable + rear dormer £110k–£170k; mansards £130k–£220k. Postcode (Zone 1 vs Zone 3), specification tier and structural complexity move you within the range.

Roughly £2,400–£4,600 per m² turnkey depending on type. Velux conversions are the cheapest per m² because the roof structure stays in place. Mansards are the most expensive because the entire rear roof is rebuilt. The calculator gives you a tailored £/m² number based on your postcode and spec.

Most London loft conversions fall under permitted development (PD): rear dormers and hip-to-gable conversions are usually allowed without planning if you stay within 40m³ added volume (terrace) or 50m³ (semi/detached), don't raise the ridge, and match existing materials. Mansards always need full planning permission. Conservation areas and Article 4 directions remove PD rights entirely.

Allow 6–10 weeks for design and planning (longer for mansards), then 8–14 weeks on site for a standard dormer, 12–18 weeks for an L-shape or hip-to-gable, and 14–20 weeks for a mansard. Most of the work is external — your house stays liveable throughout except for the final week when the staircase goes in.

Yes — typically 15–25% on the property value in central and inner-west London, often more in prime postcodes. A well-designed loft with a double bedroom + en-suite usually returns 130–200% of the build cost on resale. ROI is highest on dormers (best floor area per £) and lowest on Velux-only (limited headroom).

You need at least 2.2–2.4m head height from the existing ceiling joists to the underside of the ridge for a meaningful conversion. Less than that and you're looking at a roof raise (which loses PD rights) or a mansard. We measure on the free site visit — most Victorian and Edwardian London houses have enough.

If you're building on or near the boundary line, or cutting into a shared party wall to insert steels, you need a Party Wall Award under the 1996 Act. We serve notice on your behalf and the typical timeline is 4–8 weeks. Each neighbour appoints their own surveyor — fees usually £1,000–£3,000 per agreement and are your cost.

Yes, almost always. Loft conversions are predominantly external works — scaffolding goes up, the roof is opened from above, and the staircase is installed last. You'll have a noisy fortnight when the dormer is framed and a dusty week when the stairs go in, but you don't need to move out.