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Tall red-brick Victorian house with bay windows and a front garden on a London street

Blog: neighbours and checks

How much does a pre-purchase extension report cost in London?

By Property Architecture drawing team, chartered architectural technologists (MCIAT). Published . 3 minute read.

A pre-purchase extension report for a London house costs £189 from us, with no VAT to add. It tells you, before you offer, whether permitted development applies, what an extension could look like and what planning route it would take. The reason to ask early is simple: a restriction found after exchange cannot be undone, while one found before costs you only the fee.

From £189 total

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    Key takeaways

    What the report costs, and what it saves

    Our fee is £189. For that we check the address against the designations that change what you can build, work out what permitted development allows, set out what an extension could look like, and give you the planning route. See our pre-purchase report page for what is in it.

    It is among the less expensive things we do and among the most useful. The extension a seller's agent calls possible may already be built, may be ruled out by the location, or may need a planning application the seller does not mention.

    What the fee includesA check of the address against the main designations; Permitted development tested against the plot; A sketch of what an extension could look like; The planning route and the council's fee; A plain answer on whether to proceedWhat the fee includesA check of the address against the maindesignationsPermitted development tested against theplotA sketch of what an extension could looklikeThe planning route and the council's feeA plain answer on whether to proceedFixed fee from £189, no VAT to add
    What our pre-purchase report includes.

    What the rules allow, and where they stop

    For a single-storey rear extension, permitted development allows 4 metres beyond the rear wall if detached, 3 metres for any other houseGeneral Permitted Development Order 2015, Schedule 2, Part 1, Class A. With prior approval, the limit rises to up to 8 metres beyond the rear wall if detached, or 6 metres for any other houseGeneral Permitted Development Order 2015, Schedule 2, Part 1, Class A, paragraph A.1(g). Beyond those, or on a house that does not meet the conditions, a planning application is needed.

    The report measures the plot against those limits from records and the street, so you know early whether the extension in the agent's brochure would be allowed. It is not a substitute for a survey, which comes after you own the house, but it is enough to price an offer.

    Brick period houses on Downshire Hill in Hampstead with sash windows and a front garden wall
    Period streets are often in conservation areas, which is the first thing the report checks. Photo: Images George Rex, CC BY-SA 2.0

    The traps the report looks for

    The first is history. The limits are measured from the original house: a building as it was built, or as it stood on 1 July 1948 if it existed thenGeneral Permitted Development Order 2015, article 2. A house that already has a large extension may have none of its allowance left, whatever the brochure suggests.

    The second is the location. A council can switch rights off for an area: a council may direct that permitted development rights in a class do not apply to an areaGeneral Permitted Development Order 2015, article 4. An article 4 direction only means that development needs an application, not that it is forbidden: it only means development cannot be carried out under permitted development and needs a planning applicationGOV.UK planning practice guidance, When is permission required?. The third is the legal timing: such a direction cannot stop development already begun or built: article 4 directions cannot prevent development that has been commenced or already carried outGOV.UK planning practice guidance, When is permission required?.

    What it means for the money

    If permitted development works, a certificate is optional proof and costs the council half the full application fee, with our drawings from £629. If prior approval is the route, the council charges £249GOV.UK, Fees for planning applications in England from 1 April 2026. If a planning application is needed, the fee is £548GOV.UK, Fees for planning applications in England from 1 April 2026.

    Those figures, with the survey, drawings and structure, are what you set against the price of the house. Our cost posts for rear extension drawings and loft conversion drawings give the next level of detail.

    How the job runs, step by stepSend us the address you are thinking of buying Then: Constraints checked: conservation area, article 4, listing and more Then: Permitted development tested against the plot Then: What an extension could look like sketched Then: Planning route and council fee set out Then: Report issued before you offerSend us the address you are thinkingof buyingConstraints checked: conservationarea, article 4, listing and morePermitted development tested againstthe plotWhat an extension could look likesketchedPlanning route and council fee set outReport issued before you offer
    From the address to an answer you can use before you offer.

    For buyers comparing several houses

    Investors and landlords often want the same answer for several properties. Each report is separate and fixed, and the answers can be compared on the same basis. If a property looks promising, a feasibility study draws the options.

    We will tell you plainly when the answer is no. That is the point of asking.

    The figures, with sources

    Permitted development limit for a single-storey rear extension
    4 metres beyond the rear wall if detached, 3 metres for any other houseGeneral Permitted Development Order 2015, Schedule 2, Part 1, Class AChecked 25 October 2026
    Larger home extension limit, single storey, with prior approval
    up to 8 metres beyond the rear wall if detached, or 6 metres for any other houseGeneral Permitted Development Order 2015, Schedule 2, Part 1, Class A, paragraph A.1(g)Checked 25 October 2026
    Meaning of the original house
    a building as it was built, or as it stood on 1 July 1948 if it existed thenGeneral Permitted Development Order 2015, article 2Checked 25 October 2026
    Article 4 directions
    a council may direct that permitted development rights in a class do not apply to an areaGeneral Permitted Development Order 2015, article 4Checked 25 October 2026
    Effect of an article 4 direction
    it only means development cannot be carried out under permitted development and needs a planning applicationGOV.UK planning practice guidance, When is permission required?Checked 25 October 2026
    Article 4 and work already started
    article 4 directions cannot prevent development that has been commenced or already carried outGOV.UK planning practice guidance, When is permission required?Checked 25 October 2026
    National planning fee, extension or alteration to a single house
    £548GOV.UK, Fees for planning applications in England from 1 April 2026Checked 25 October 2026
    National fee, prior approval for a larger home extension
    £249GOV.UK, Fees for planning applications in England from 1 April 2026Checked 25 October 2026

    Questions

    Is this the same as a survey?

    No. A survey inspects the building's condition. This report is about what you could build. It works from records and the street, so you can get it before you have access.

    How quickly can I have it?

    We confirm the timing when you order. Buyers often need an answer before an offer is made, so tell us your deadline.

    Can you tell me if the house has already been extended?

    Planning history and the street view often show it. If it is unclear, we say so and advise on a survey after purchase.

    What if the answer is no?

    Then you have saved yourself from paying for an extension the house cannot take. We explain what could be built instead.

    Header photo: A tall red-brick Victorian house with bay windows and a front garden on a London street by Lorenc Memaga, Pexels License.

    The fixed fee for pre-purchase "can i extend?" reports

    Fixed fee
    from £189
    Total you pay
    from £189

    No VAT to add. The fee is fixed in writing after a free constraints check of your address.

    What you get

    • A check of the address against the main designations
    • Permitted development tested against the plot
    • A sketch of what an extension could look like
    • The planning route and the council's fee
    • A plain answer on whether to proceed
    • More about our pre-purchase "can i extend?" reports
    Request your fixed quoteCall 020 7131 9703
    Terrace of yellow-brick Victorian cottages with white sash windows and red door surrounds on a London street

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    Tell us about your property.

    We check the constraints, then send a fixed fee. Messages before 3pm get a reply the same working day.

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