Property Intelligence
Independent property intelligence, built on live UK cost data — for buying, extending, renovating, checking a quote, or selling.
Inside a BuildLens report
The Verdict
42 Thornfield Rise, Blackheath, London SE3
Total renovation cost
£196,564
Range: £177,000 – £216,000
Summary by trade
+ nine further trades, contingency and professional fees — every line itemised
Figures from the BuildLens Full Spectrum sample report — a 145 m² 1930s semi-detached house in SE London.
Independent property intelligence, built on live UK cost data — for buying, extending, renovating, checking a quote, or selling.
The cost gap
On a typical London rear extension, the estimate says £80,000. The builder's quote comes in at £128,000. The final bill lands at £192,000. The cost was always going to be the cost — the only question is whether you knew it before you committed, or found out halfway through, with the money already spent. BuildLens gives you the real figure on day one, built on live UK cost data.
Representative figures for a London rear extension; the real spread varies by property and scope.
Three questions. Three starting points.
Most people guess. 42% choose the wrong option, and the difference is typically six figures.
£49 Get your answer → Ready to buildBuild and renovation costs are underestimated by 30–50% on most projects. Get the real number before you commit.
From£199 Compare reports → Market intelligence14 weeks on the market and no offers? There is usually a reason hidden in the numbers. We surface it — with evidence, not opinion.
From£129 Get your diagnosis →
Eight reports across Build Cost and Market Intelligence. Works with whatever plans you have.
See the full BuildLens Library →
The BuildLens Library
Every BuildLens report is built for one property and one decision, from live UK cost data. Prices are fixed, delivery is under 48 hours, and each report is listed below with what it answers.
What your build, extension or renovation will really cost — before you commit.
When a house is not selling, the reason is usually in the numbers.
For buying a house that needs work. In build — the waitlist is open.
Eight in ten renovation projects exceed their original budget.
The gap between what a project is expected to cost and what it actually costs routinely runs into six figures.
Whether it is a rear extension in London, a loft conversion in Manchester, or a full renovation of a Victorian terrace in Hull, the gap between estimate and reality is consistent, and it is predictable.
BuildLens exists to close it.
What sits behind the number
01
Live merchant pricing, tracked weekly across UK suppliers, set against current trade labour rates. Not national averages — the cost of materials and labour as they stand now, calibrated to your postcode.
02
Victorian terraces to new builds, rear extensions to full renovations. Buying a house that needs work, pressure-testing a quote before you commit, or working out why a house is not selling.
03
Postcode-calibrated analysis delivered to your inbox. No site visit needed. Works from architects' drawings, a listing floor plan, or a hand-drawn sketch.
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From a quick extend-or-move read at £49 to the most comprehensive cost intelligence report at £975. Whatever stage you have reached, there is a report built for it.