Double-storey rear extension on Edwardian terrace
Hammersmith and Fulham · W6 · Brackenbury Village Conservation Area · 26-week build
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Brief
A 4-bed Edwardian terrace in Brackenbury Village (W6) — Article 4 direction zone — needed a major rear addition. The clients wanted a 28m² kitchen extension at ground floor and a 26m² master suite at first floor (over the new ground-floor footprint), plus comprehensive internal reconfiguration. Brackenbury's Article 4 direction removed PD rights — every roof and rear elevation alteration required full planning with conservation officer engagement.
Challenge
Brackenbury Village's Article 4 direction is one of the strictest in inner west London — full planning required for any rear extension, dormers, rooflights, render changes, even window replacement. The H&F conservation team initially resisted a full-height brick double-storey, preferring a single-storey approach. Pre-app submission demonstrated through elevation studies that the double-storey could be approved with: (1) brick first floor stepped back 200mm from ground-floor line, (2) slim-profile Crittall MW40 steel windows in lieu of aluminium, (3) recessed parapet detail at roof line to read as a 'lower-than-ridge' subordinate addition, (4) reclaimed London stock brick survey-matched to the existing terrace, (5) lime mortar joint profile matching the existing.
Solution
Pre-application advice obtained from the H&F Brackenbury conservation officer over a 6-week pre-app process. Full planning submitted with detailed elevation drawings, material specification, sample panel photographs, and Heritage Statement justifying the design. Approved at 13 weeks first-time with three conservation conditions on materials and joinery. Build: 26 weeks. Phase 1 (weeks 1–4): demolition of existing 1970s sun-room and conservatory, structural opening up. Phase 2 (weeks 4–12): foundations, steel structure (3.8 tonnes total — goalpost at ground, beam at first-floor, ridge), masonry to wall-plate. Phase 3 (weeks 12–18): roof, sashes, Crittall installation. Phase 4 (weeks 18–26): internal fit-out — kitchen, ensuite, bathroom, M&E, decoration.
Outcome
Planning approved first-time after pre-app — significant given the Article 4 status. Build delivered in 26 weeks against a 26-week programme. Final floor area increased from 162m² to 216m² (+54m²). Conservation officer attended four site visits during construction and signed off all heritage details on site. Independent valuation uplift £465,000 against £248,000 spend.
Spec
Project specification.
Gallery
Inside the build.
"We were told a double-storey extension in Brackenbury would be impossible. Builderr's planning team built the case through pre-app and got it approved first-time. The conservation officer was on site four times during the build to inspect brick joints, sash profiles and slate detailing — they signed off every element. The extension reads as if it were always there."
— Felix and Astrid Brennan, Brackenbury Village W6
Builderr vs other London builders.
The construction industry has a wide distribution of operators. Here's what changes between a directly-employed, fixed-scope outfit and the alternatives.
| Criterion | Builderr | Typical London builder | Cowboy outfit |
|---|---|---|---|
| Labour model | Directly employed team (PAYE) | Mixed subcontract gangs | Day-rate cash labour |
| Pricing | Fixed-scope itemised quote | Estimate + provisional sums | Verbal price + variations |
| Design & engineering | In-house architect + SE | Outsourced, separate billing | Builder draws on the back of an envelope |
| Planning + LDC handled | Yes — included in price | Often charged extra | Builder asks you to apply |
| Party wall surveyors | Instructed by us | Your responsibility | Skipped (illegal) |
| Building control | Plans + site inspections booked by us | Building Notice route | Not registered |
| Project management | Dedicated PM, weekly photo updates | Foreman doubles up | Owner-manager juggles 5 jobs |
| Payment schedule | Stage payments against signed-off milestones | Weekly invoices | Cash up front |
| Insurance | £10M PL + 10yr structural warranty | £2–5M PL only | No documented cover |
| Snags at handover | <3 typical | 20–30 typical | Walk-off mid-job common |
| Variation creep | 0% — fixed scope | +15–25% over original quote | +40%+ regularly |
Save £49,600–£111,600 on a double-storey rear extension.
Industry data (FMB, RICS, Which? Trusted Trader 2024) shows the average London construction project overruns by 18–22% on cost and 25–35% on time. Fixed-scope contracts with a single accountable team eliminate that variance. The savings above assume a typical project at £248,000.
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