London's most popular loft type — the full-width rear dormer. Planning or Permitted Development route assessed for your Westminster property, building regulations, structural steelwork and Party Wall notices, all fixed fee.
London's most popular loft type — the full-width rear dormer. Planning or Permitted Development route assessed for your Westminster property, building regulations, structural steelwork and Party Wall notices, all fixed fee.
Housing stock in Westminster: Grand Georgian and Regency terraces in Belgravia and Pimlico; Victorian and Edwardian mansion blocks; heritage-rich townhouses throughout; very high listed building density.
Character: Heritage-first planning approach; listed buildings on almost every street; basement and rear extension policies particularly strict.
Article 4: Multiple Article 4 Directions — office-to-residential restrictions, HMO conversions, retail to residential in shopping zones.
Basement policy: Westminster basement policy restricts to single-storey, typically under 50% of rear garden footprint; lightwells and rooflights strictly controlled in conservation areas.
We confirm whether your Westminster rear dormer qualifies for Permitted Development — checking volume limits (40m³ terraced, 50m³ semi/detached), Article 4, conservation area and prior extension history.
If PD applies, we obtain a Lawful Development Certificate for certainty. If not, we submit full planning with Design & Access Statement to Westminster City Council.
Full-width flat-roof rear dormer with matching materials, set in from party walls, cheeks clad to match existing roof — the design that Westminster City Council approves most readily.
Part B fire escape (protected staircase, fire doors, smoke alarms), Part K staircase, Part L insulation, Part E acoustic separation.
Steel ridge beam, purlin supports, dormer framing, floor joist upgrade — chartered engineer sign-off for Building Control.
Most rear dormers in Westminster's terraced streets trigger Section 6 Party Wall notices. We draft, serve and coordinate the process.
Single planning or regs submission.
Planning + building regs + structural.
Listed, conservation, complex sites.
Direct answers to the questions Westminster homeowners ask every week about rear dormer drawings.
Start a free quote →It depends on your exact address in Westminster. Most standard loft conversions qualify as Permitted Development (no planning permission needed) if under 40m³ for terraced or 50m³ for semi-detached, with matching materials and 20cm eaves setback. However Westminster has Article 4 Directions that may remove these rights — and flats, conservation areas and listed buildings always require full planning. We confirm permitted development eligibility at the free feasibility visit. Full-width rear dormers are the most common PD loft type in Westminster — provided the volume, materials and setback conditions are met. We check every condition before committing to a route.
Our fixed-fee architectural package for a Westminster rear dormer starts at £1,225 (drawings + building regs + structural). Typical build costs in Westminster are £45,000–£70,000 for a standard full-width rear dormer with en-suite, depending on access, floor area and specification.
A full-width rear dormer in Westminster typically adds 15–25 square metres of habitable floor area — enough for a double bedroom with en-suite, or two single bedrooms. The flat roof gives full standing height across the entire width of the house, unlike a rooflight-only conversion which is constrained by the roof pitch.
Rear dormers in Westminster's conservation areas usually need full planning permission because PD rights are restricted. However, because they face the rear (not the street), Westminster City Council typically views them more favourably than front dormers or mansards. A well-designed rear dormer with matching materials and sensitive proportions has a strong approval record.
A standard rear dormer in Westminster takes 8–12 weeks to build once on site. Our architectural package takes 3–5 weeks from instruction to submission. Building Control approval adds 2–4 weeks. Total timeline from survey to move-in: approximately 4–5 months.
We cover every London borough with the same fixed-fee approach. If your property sits on a boundary, here are the neighbouring options.
We cover every architectural technology service in Westminster with one chartered team.
From £840. A fixed-fee, end-to-end service — measured survey, scaled drawings, Design & Access Statement where required, Planning P...
From £840. A construction-ready drawing package compliant with every Approved Document — Part A structure, Part B fire, Part L ther...
From £1,225. Every loft type across every {location} roof line — dormer, mansard, hip-to-gable, L-shape, Velux. LDC or full planning ...
From £1,225. The whole spectrum — rear extensions, side returns, wraparounds, double-storey, basement digs. Planning-led design with ...
From £1,575. {location}'s most space-efficient loft solution when PD-route dormers are blocked. Our chartered team designs mansards t...
From £995. Turn your unused {location} garage into a bedroom, home office or open-plan kitchen-diner. Planning route assessment, fu...
From £1,950. Full architectural technology service for basement digs and cellar conversions in {location} — structural underpinning d...
From £350. Chartered structural engineer calculations for every residential intervention in {location} — steel beams, lintels, pad ...
From £450. End-to-end Party Wall Act 1996 service for {location} — Section 1, 3 and 6 notices, schedule of condition surveys, party...
Free quote in 60 seconds. Fixed fee from £1,225. MCIAT chartered.
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