What we build in Marylebone
Most Marylebone projects we scope fall into three buckets: a side-return or rear infill that fixes a dark galley kitchen, a full-width rear extension that opens the ground floor to the garden, and a rear-plus-loft package that adds a bedroom while the scaffold is already up. Grade-II stucco terraces, mansion blocks and mews houses — many in conservation areas.
Extension costs in Marylebone
A mid-spec 25 m² extension in Marylebone typically lands between £140,000 and £210,000 all-in — that figure includes professional fees, planning and Building Control, party wall, a 12% contingency and VAT at 20%. Ex-VAT build rates run £3250–£4950 per m² depending on glazing, structural spans and kitchen spend.
| Project | Size | Marylebone all-in |
|---|---|---|
| Side return infill | 15–20 m² | £105k – £158k |
| Full-width rear | 20–30 m² | £140k – £210k |
| Wraparound | 30–45 m² | £203k – £305k |
| Double-storey rear | 40–60 m² | £273k – £410k |
Planning permission in Marylebone
Westminster City Council is one of the strictest in London. Article 4 removes many permitted development rights; expect a full householder application and heritage-officer consultation for anything visible from the street.
Before you assume permitted development applies to your street, check whether your street falls inside a conservation area or an Article 4 direction — both are common in Westminster and both remove PD rights for rear and side extensions. Our London planning guide walks through the tests in order.
Party wall and neighbours
Terraced and mansion-block context means a Party Wall Award is effectively guaranteed, often with two adjoining owners.
Serve notice at least two months before you break ground. Budget £1,200–£2,400 per adjoining owner if they dissent and appoint their own surveyor — see the Party Wall Act guide.
Access, logistics and site set-up
Rear access via a side alley or garden gate speeds up muck-away and cuts labour cost noticeably.
Every quote we issue for Marylebone prices skip permits, parking suspensions, protection and welfare explicitly in the preliminaries — so the number you sign is the number you pay.
Value added in Marylebone
Adding floor area is usually cheaper than moving once stamp duty, agent fees and moving costs are counted.
Typical programme
- Weeks 0–4Measured survey, design and structural calcs
- Weeks 4–12Planning or lawful development certificate, party wall notices
- Weeks 12–16Tender, builder selection and contract signing
- Weeks 16–34On site: groundworks, shell, watertight, first and second fix
- Week 35Building Control sign-off, snagging and handover
Full detail in the London extension timeline guide.
Why homeowners in Marylebone use us
- KYB-verified builders only
- Live Westminster project experience
- Itemised fixed-price specifications
- Insurance, warranty and accreditation checks