Purley 1930s Double-Storey Side + Rear Extension
1930s semi, double-storey side, single-storey rear, open-plan reno
Brief
A family of four in a 3-bed Purley 1930s semi needed downstairs entertaining space and an additional bedroom + en-suite upstairs. The brief: double-storey side extension + single-storey rear + open-plan ground floor remodel. No conservation area; PD route attractive.
Challenge
Outer London delivery logistics: tighter labour pool and longer lead times on specialist trades than inner London. Sloping plot — rear garden 1.1m higher than ground floor — required stepped foundations and a half-flight lift between dining area and garden door. Existing party wall to north neighbour needed Party Wall Act notices (single Surveyor route agreed, £1,400). Family wanted to remain in occupation throughout — necessitated phased works with temporary kitchen for 9 weeks.
Solution
Double-storey side extension 3.4m × 7.8m: ground floor extending kitchen, first floor adding 4th bedroom + en-suite. Single-storey rear 4m × 5.6m for living-dining with 5m bifolds and double roof lanterns. Ground floor fully open-plan from front to back. Stepped foundations stepped 600mm at rear due to slope. Half-flight of three steps internal between dining and garden floor — turned into a feature with built-in seating and timber detail. Phased works: side extension first (kitchen + bedroom roughed out); 2-week kitchen relocation to side extension; rear extension built; final fit-out.
Outcome
Internal floor area increased from 94m² to 145m² (+54%). Family remained in occupation throughout — no rental costs. Full PD route saved 8 weeks vs full planning. Phased programme came in 22 weeks. EPC C maintained (1930s cavity walls already insulated). Family Christmas in the new open-plan space before site completion.
Spec
Project specification.
Gallery
Inside the build.
"We were anxious about staying in occupation during such a big build but Builderr's phased approach worked. The double-storey side gave us the extra bedroom we'd been priced out of getting in a bigger house and the rear extension means the kitchen-living-garden flows the way modern family life actually works. PD route saved us months."
— Steve and Priya Walters, Purley CR8
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 £37,000–£83,250 on a 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 £185,000.
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