Side return + double-storey extension
Greenwich · SE3 · Blackheath Conservation Area · 24-week build
Brief
A 4-bed Victorian semi in the Blackheath Conservation Area needed expansion for a family of four wanting to remain in the borough. The scope: side return kitchen extension at ground floor, double-storey side extension at first and ground floor, full first-floor refurbishment with master ensuite and family bathroom relocation, restored sashes, new heating.
Challenge
Blackheath Conservation Area imposes strict design rules: London stock brick to match the existing facade, natural Welsh slate, sash window matching, no aluminium framing visible from the street. The double-storey extension required pre-application engagement with the Greenwich conservation team — they initially resisted full-height matching brick, preferring a recessive 'subordinate' design. Final design: brick first floor stepped back 150mm with a deeper recessed reveal, slim Crittall-profile steel windows, slate roof tied into the existing main roof at a lower ridge.
Solution
20-week site build with the Blackheath conservation officer attending three site visits during construction to sign off material samples. Foundations: reinforced concrete strip with mass concrete underpinning to the existing party wall at the double-storey side. Steel structure: 2.4 tonnes total — goalpost at side return rear, ridge beam, double-storey upper floor beam supporting first floor and roof loads. Heritage brick from reclaimed London stock yard — 4,200 bricks survey-matched to the existing facade colour and weathering. Welsh slate from Penrhyn quarry, lead flashings to all valleys and ridges. 22 sashes restored on the existing house plus 6 new sashes matching the original profile (Sash Window Workshop bespoke joinery). Crittall MW40 steel windows in the new openings, finished anthracite grey. MVHR hidden in joist void; air source heat pump replacing the old gas boiler.
Outcome
Planning approved at 12 weeks first-time after pre-app, no objections from neighbours. Build delivered in 24 weeks against a 24-week programme. EPC improved from band D (62) to band C (78). Final floor area increased from 158m² to 218m². Independent valuation uplift £420,000 against £215,000 spend.
Spec
Project specification.
Gallery
Inside the build.
"Blackheath is known as one of London's harder conservation areas. Builderr's pre-app strategy meant we knew exactly what would and wouldn't be approved before drawings were finalised. The brickwork on the new double-storey is genuinely indistinguishable from the 1880s original — the conservation officer commented on it at the final inspection."
— James and Priya Patel, Blackheath SE3
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 £43,000–£96,750 on a side return + double storey.
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 £215,000.
Want a build like Greenwich?
Get a fixed-scope quote with the same direct-labour delivery. Senior consultant call within one business hour.
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