Double-storey rear + mansard loft, Clapton
Hackney · 1895 Victorian terrace · E5 · 20-week build
Brief
A late-Victorian (1895) mid-terraced house in Clapton — the clients needed a large open-plan kitchen-diner at ground, a fourth bedroom at first, and a master suite at roof level. All three were delivered in a single permitted development plus full planning application.
Challenge
Hackney requires full planning permission for any double-storey rear extension (PD only allows single-storey rear), and mansard loft conversions are never permitted development because they alter the roof profile beyond Class B limits. The property sits 180m from the Clapton Conservation Area — not formally within the CA, but Hackney's Development Management Policies require material and design quality consistent with the surrounding character. A pre-application meeting with Hackney planning confirmed: London stock brick match, sash-pattern windows to upper floors, and lead-clad mansard cheeks would be required for approval.
Solution
Pre-application advice secured from Hackney's duty planner (cost £360, 3-week turnaround). Architect produced a planning package showing full material match: handmade London stock brick (Bulmer Brick & Tile, BW blend) to double-storey rear, matching the original stock facing. First-floor rear windows — two no. vertical sash in thermally-broken aluminium with narrow sightlines (Kloeber origin profile). Mansard with 72° main pitch, 6mm lead-clad cheeks, and flush Velux rooflights to rear slope. Planning submitted; case officer requested one amendment — chimney pot retention on the party wall stack (structural survey confirmed it was hollow; Builderr retained the pots as feature only). Full planning permission granted 8 weeks after submission. Structurally, two RSJs carry the double-storey rear (6m span, calculated by in-house structural engineer); the mansard steel frame was fabricated off-site and craned in on day 2 of loft works.
Outcome
60m² added across three levels: 19m² kitchen-diner (ground), 19m² bedroom 4 (first), 22m² master suite (mansard). Kitchen-diner has 3m aluminium bifold to garden and 600mm roof lantern over island. Bedroom 4 is south-facing with a Juliet balcony. Mansard master suite has walk-in wardrobe and ensuite with freestanding bath. Building regulations: full plans application, building control sign-off at completion. Property valued at £1.42m post-completion (from £870k before works). Total programme 20 weeks.
Spec
Project specification.
Gallery
Inside the build.
"We were told a mansard plus double-storey rear in Hackney needed a fight with the planners. Builderr's pre-app meeting meant the planners told us exactly what they wanted and we gave it to them. One minor amendment, then approval. Completely stress-free."
— Kofi and Abena Mensah, Clapton E5
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 £38,400–£86,400 on a loft conversion.
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 £192,000.
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Get a fixed-scope quote with the same direct-labour delivery. Senior consultant call within one business hour.
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