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Harrow, London

Biodiversity net gain plans in Harrow

Harrow is a borough of long gardens, with 34.7 per cent of its land in domestic gardens, so a new home on a back plot here is a real net gain question. The council's validation checklist lists a net gain assessment as mandatory under the Town and Country Planning Act and adds no local figure: Statutory only. Extensions and lofts are exempt. We quote after a free constraints check.

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    Architectural model of a four-storey London stucco townhouse in its terrace, with a portico, area railings, sash windows, a cornice and chimney stacks
    The house as it stands: four storeys over a lower ground floor.Existing Proposed worksAn illustrative model, built for this page.

    How we work on biodiversity net gain plans

    Seven steps from first call to approval.

    The same model cut through the middle: every floor, the stair, the chimney breasts, the new mansard, rear extension and basement in section
    Section through the model: every floor on one datum.

    1. Enquiry and constraints check

      We check the property against conservation areas, listed status, Article 4 directions, tree preservation orders, flood zone and planning history. We choose the right route and send a fixed quote.

    2. Measured survey

      We survey the house on one datum: rooms, levels, boundaries, drains, trees and the neighbours' windows that the 45° and 25° tests depend on.

    3. Design options

      We model the house in Revit and show you options in 3D and plan, with the planning strategy and the precedents in your street.

    4. Design frozen

      You choose an option in writing. Nothing changes after this without your say.

    5. Independent check

      A second chartered technologist checks every sheet against the council's validation checklist and the policy. A senior review signs it off before anything is submitted.

    6. Submission

      We prepare the forms, certificates, fee and documents and submit through the Planning Portal.

    7. Officer liaison

      We answer the planning officer and make any amendments within five working days, at no charge until approval.

    Free redraws until approval. Every drawing set is checked independently, and the checker is never the person who drew it.

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    Brick cottage with a tiled roof, chimneys and a front dormer window

    What Harrow's validation checklist says

    Harrow's national and local validation checklist lists a Biodiversity Net Gain Assessment as mandatory under Schedule 7A of the Town and Country Planning Act 1990, as inserted by the Environment Act 2021. It says the assessment should cover habitat types and may need a Preliminary Ecological Appraisal or an Ecological Impact Assessment. The council's recorded value is Statutory only, meaning the statutory rules and nothing more.

    The appraisal point is the useful one. Where a site holds anything beyond ordinary lawn, such as a pond, an old hedgerow, a mature tree group or signs of bats, the council can ask for a wider ecological report. That report is separate from the metric, costs more, and takes a season to do if the site needs a seasonal survey.

    We screen for those features at the free check, so you hear about a possible appraisal before you pay for design work.

    Because the checklist is brief on detail, the borough's officers rely on the national guidance and the metric itself. A tidy, well-labelled file with clear parcel references saves them time, and it is the quickest way to avoid a request for further information after validation.

    Rear view of brick terraced houses in London with slate roofs and chimney stacks along the shared roofline

    Local figures for Harrow

    Figures with their unit, period and source
    MeasureValuePeriodSource
    Biodiversity Net Gain Assessment listed as mandatory under Schedule 7A of the Town and Country Planning Act 1990 (as inserted by Environment Act 2021); it should cover habitat types and may need a Preliminary Ecological Appraisal or Ecological Impact Assessment. No higher local percentage stated.Statutory only—harrow.gov.uk, Harrow National and Local Validation Checklist of Planning Applications (1 February 2024), pdf p.10, row 'Biodiversity Net Gain Assessment'
    Domestic gardens share of land (GLUD 2005)34.7 % of land that is domestic garden (GLUD 2005)2005data.london.gov.uk
    Green Belt share of the council area22 % of council area covered by green-belt polygons—planning.data.gov.uk
    Households living in a house65.4 % of households living in a house or bungalow (detached, semi-detached or terraced)Census 2021nomisweb.co.uk
    Conservation areas31 named conservation areas published by the council—planning.data.gov.uk
    Listed building entries295 list entries (Historic England, within the LPA boundary)—planning.data.gov.uk
    Householder applications granted81.7 %1 July 2025 - 30 June 2026assets.publishing.service.gov.uk
    Environment Act 2021 Sch 14 para 2, inserting Sch 7A TCPA 1990: 'relevant percentage' 10%10 %—legislation.gov.uk
    'Developments of 0.2 hectares or below': from 6 August 2026 BNG does not apply where the site area within the red line boundary is 0.2 ha or below0.2 ha—gov.uk
    Sch 7A para 9(3) as inserted: enhancement maintained for at least 30 years after completion30 years—legislation.gov.uk

    A blank value means the figure has not been published, not that there are none. Check your own address with the council.

    Councils bordering Harrow
    Which application your project needsLawful Development Certificate decision: 8 weeks. Prior approval decision: 42 days. Householder decision: 8 weeksYour projectWithin permitted development?Lawful Development CertificatePrior approvalHouseholder applicationYesLarger rear extensionNoABC

    Which application your project needs

    The usual route for a house; flats and listed buildings follow other rules.

    A · Lawful Development Certificate decision
    8 weeks
    B · Prior approval decision
    42 days
    C · Householder decision
    8 weeks

    Large gardens, and what happens when they are built on

    With 34.7 per cent of the borough in gardens and 65.4 per cent of households living in a house, Harrow is exactly the kind of place where owners consider a house in the garden, a coach house or a block at the bottom of a long plot. Those are the schemes net gain was written for.

    A long suburban garden is often a mosaic: lawn, shrub beds, a fruit tree or two, a boundary hedge, a shed and a patch of rough ground at the end. Each parcel scores differently, and the way a design cuts into the plot decides how many units are lost. Placing a house toward the street end, and keeping the rough ground and mature trees at the back, usually costs far less than the reverse.

    Our new build drawings include the site and landscape sheets that show those choices.

    There is a design benefit too. A plot developed with care keeps its character, with the garden's best trees and hedges screening the new building from the neighbours. That is good for habitat and for the planning case, because officers weigh outlook and screening alongside the metric.

    Green Belt, conservation areas and policy

    22 per cent of Harrow is Green Belt, and the borough has 31 conservation areas and 295 listed building entries.

    The borough's Harrow Local Plan 2021-2041 was adopted in 2,026, and the Residential Design Guide SPD sets the design rules for extensions and new homes. We read both with the metric so that the plan, the drawings and the guidance agree.

    If the case for the house itself is the harder question, our planning consultant service can lead it.

    Who is exempt in Harrow

    Householder applications and permitted development are exempt. Sites of 0.2 hectares or below are exempt, and many Harrow back plots are small enough to qualify. Impacts below 25 square metres of habitat are excluded under the de minimis rule.

    In the latest returns the council granted 81.7 per cent of householder applications and decided 93.7 per cent in time. Even when you are exempt, the form must say why.

    Price and next step

    A plan has no list price, because the cost follows the habitats and any appraisal. You receive a fixed quote after a free constraints check.

    Our biodiversity net gain page covers the national rules, and the Harrow area page lists the other services we offer in the borough.

    What you receive

    Planning drawing sheet for a rear extension with plans, elevations and sections
    Sample drawing. Planning drawings for a rear extension: plans, elevations and sections on one sheet set.
    Pencil resting on a dimensioned technical drawing beside a scale rule
    The street around you
    Move across the plinth — the blocks rise around the pointer.

    Other services in Harrow

    Biodiversity net gain plans nearby

    Questions

    Does Harrow ask for more than the statutory gain?

    No. The checklist records Statutory only and states no higher local percentage.

    Might I need an ecological appraisal as well?

    Possibly. The checklist says the assessment may need a Preliminary Ecological Appraisal or an Ecological Impact Assessment.

    Can I build a house in my back garden?

    Sometimes. It needs planning permission, and unless the plot is 0.2 hectares or below it also needs a net gain plan unless another exemption applies.

    How long is the gain kept?

    At least 30 years after completion.

    Sources and dates

    City of London skyline glowing at dusk across the Thames under a dramatic orange sky

    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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