Loft conversion cost
in Marylebone.

Marylebone Conservation Area covers the bulk of W1 north of Oxford Street. Many properties are listed or estate-managed with their own design covenants. Outside conservation areas, most rear-dormer conversions in Marylebone qualify for permitted development (PD) within the 40m³ (terrace) or 50m³ (semi/detached) volume limits. Mansards always need full planning. We check your specific address before quoting and submit the application on your behalf.

Significantly — the Howard de Walden and Portman estates have their own design covenants in addition to Westminster planning. Estate approval is required before planning is submitted, and the estate's design preferences often go beyond what planning policy strictly requires. We work to estate-approval standards from the design phase onwards.

Typical timeline: 6–10 weeks for design and planning (longer in conservation areas like much of Marylebone), 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. City of Westminster processes PD-route Lawful Development Certificates in approximately 8 weeks.

In W1, a well-executed loft conversion typically adds 15–25% to property value — often more in prime postcodes. The ROI is strongest when you add a double bedroom plus en-suite, which is the standard L-shape dormer configuration. Property uplift on a £54k–£264k build commonly exceeds the build cost by 30–60%.

Yes — Marylebone is within our core London catchment. Our studio is at 20 Dawes Road in Fulham, 6.0km from Marylebone. We've delivered loft conversions across the W1 postcode and our subcontractor network covers Westminster. Free site visit, fixed-price quote, 10-year HomePro guarantee on the finished work.