The real cost of your extension, before you get a single quote.
Type your address. In seconds you will know whether it can be extended and if it needs planning. The £12 report then prices every line of the job.
Free. We read the public registers for the address; nothing is stored until you ask for the full check.
- Free instant check, any London house
- Full report £12, in about a minute
- Money back, if it is not useful
How it works
The first step is free.01Type your address
Free: the registers give the borough, any conservation area and the likely planning route.
02Answer ten questions
Size, finish and extras, and you see what we found about the house before you pay.
03Read your report
£12 for every cost line, the planning route and a timeline, with free changes for 30 days.
The full report, £12
Every figure from the same engine, inc VAT.- Low, likely and high totals, every line priced
- Architect, engineer, council and party wall fees
- The planning route, and what would change it
- A timeline from today to moving back in
- What moves the price, and what to ask anyone who quotes
Not useful? Reply to your report email within 14 days and we refund it, no questions asked.
What does it cost where you live?
32 boroughsTypical jobs in
Brent
| Job | Size | All in, inc VAT |
|---|---|---|
| Single-storey rear extensionExpected £80,000 | 17.5 m² | £62,000 to £98,000 |
| Side-return extensionExpected £60,000 | 10.8 m² | £46,000 to £75,000 |
| Loft conversion with a rear dormerExpected £81,000 | 28 m² | £63,000 to £99,000 |
Mostly Victorian and Edwardian terraces, with interwar semis towards Kingsbury and Wembley. Build rates here sit at our London baseline.
Every borough has its own page with the three jobs priced for its housing, by finish. All 32 boroughs
Questions people ask before they pay
Is this a quote?
No. It is an estimate: a low, likely and high figure for your job, built from your answers, the public records for your address and current London rates. A quote comes from a builder who has seen the house. The report tells you what a fair quote should look like, and what to ask when one arrives.
How close to reality are the numbers?
They are ranges on purpose. The rates are current London trade rates, and the report itemises the schedule of works so you can see what drives the total. Ground conditions, the state of the existing house and your choices of kitchen and glazing decide where in the range you land, which is why the report also tells you what moves the price.
What do you look up about my house?
The borough and coordinates for your postcode, the Energy Performance Certificate record (house type, floor area, age band, whether it has been extended), and the planning register for conservation areas, Article 4 directions, flood zones and nearby listed buildings. Everything is public data, and you see what we found before you pay.
Do you pass my details to builders?
No. Nobody contacts you. Your answers and email are used to write and deliver your report and your receipt, and for nothing else.
What if I live in a flat, or the report cannot be written?
Flats have no permitted development rights, and the report says so and prices the job on the assumption of a planning application. If the report fails to generate after payment, you are refunded in full and automatically.
What if it is not useful?
Not useful? Reply to your report email within 14 days and we refund it, no questions asked. And within 30 days you can change your answers, a different finish, a bigger footprint, a loft instead of an extension, and have the report written again at no cost.
Can I use it for a client?
Yes. Choose "I am an architect, designer or builder acting for a client" in the questionnaire and the report is written to you as a peer, with ex-VAT figures alongside, and the practice name on the front. Cost My Extension is independent: it does not sell leads or recommend builders.