How we calculate this.
Every number on Plotted is an estimate, not a quote or a valuation. Here's exactly where the figures come from and where they stop being reliable.
Build cost estimates
Our core rates are sourced directly from working builders in Surrey and West London and refreshed as we collect more completed-job data. Rates are quoted per square metre, ex VAT, for the structural shell only — for example single-storey extensions at £2,500–£3,000/m², and double-storey work at 1.75× the single-storey rate where both floors are built together.
On top of the shell we add itemised allowances for the things builders routinely exclude: electrics, glazing, decorating and scaffolding. We then apply 20% VAT so the headline figure is an all-in cost, and widen the range to reflect site conditions, access and specification.
Postcode multipliers adjust for local labour pricing (for example central London commands more than outer Surrey). Categories where we don't yet hold verified builder pricing are clearly labelled as benchmark figures.
Property value estimates
We start from Land Registry sold-price benchmarks for your postcode district and property type, then blend in live comparable listings scraped at the time you run the tool — filtered to bedroom-matched properties on or near your street and weighted towards the top quartile, since a renovated home sits at the upper end of its local range.
Uplift percentages for each renovation type follow RICS-aligned reasoning on how much of a spend is typically recovered on sale, adjusted for the local ceiling price. Cost recovered is simply value added divided by estimated build cost.
Materials, ROI and lifespan
Standard, Premium and Luxury tiers use published manufacturer lifespan data and typical UK supply-and-fit pricing. The £ added figure assumes the finish is appropriate to the property's value band — over-specifying beyond the local ceiling reduces recovery, which the model reflects.
AI room scans
Photo scans use a vision model to read approximate room dimensions and condition from your image. Dimensions are inferred, not measured, and renders are illustrative visualisations — not plans, surveys or product guarantees.
Where our estimates stop
We can't see your ground conditions, drainage, party wall issues, planning constraints or the state of your existing structure. Any of those can move a real quote well outside our range. Treat Plotted as a way to sanity-check a budget before you speak to builders — not as a replacement for a site visit, a RICS valuation or a written quote.