Double-storey extension
Richmond · Detached family home · 19-week build
Brief
Detached family home in Richmond — wanted an additional bedroom and ensuite plus a kitchen-diner with garden connection. Site allowed for 4m depth across the full rear width.
Challenge
Mature oak 8m from the rear corner — clay site with NHBC tree-table requirements pushing foundations to 2.5m. Original foundations only 600mm deep; localised underpinning needed at the junction.
Solution
Mini-piled foundations 4m to engineered stratum, with reinforced concrete ground beam. Underpinning in 1m bays at the existing rear wall. Brick-and-block cavity wall to match existing render finish. Roof lantern over the dining zone; new first-floor bedroom suite directly above with matching window proportions.
Outcome
Planning approved at 11 weeks. Build completed in 19 weeks. Underpinning added 2 weeks vs original 17-week programme but absorbed within the agreed contingency. Resale agent valued uplift at £350,000.
Spec
Project specification.
Gallery
Inside the build.
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 £35,600–£80,100 on a double-storey 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 £178,000.
Want a build like Richmond upon Thames?
Get a fixed-scope quote with the same direct-labour delivery. Senior consultant call within one business hour.
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