barnconversioncost.co.uk

Biodiversity Net Gain cost

Build-cost bands are the site's own indicative model, inflated to a Q2 2026 footing via the ONS Construction Output Price Index (April 2026). Class Q rules current to the 21 May 2024 GPDO amendment.

Mandatory 10% BNG applies to most full planning applications since February 2024. Cost ranges from £2,000 (on-site, low-baseline site) to £12,000+ (off-site units). Class Q permitted development is not currently caught by BNG.

When BNG applies

Full planning applications validated after 12 February 2024 must demonstrate 10% biodiversity net gain measured by the statutory metric. Class Q prior approval is not on the BNG hook today; that may change in a future legislative round.

Cost stack

Baseline metric (ecologist day rate)
£700 - £1,800
Habitat enhancement plan
£800 - £2,400
On-site delivery (planting, ponds, wildflower)
£500 - £5,000
Off-site BNG units (if needed)
£8,000 - £42,000 each
30-year monitoring contribution
£1,500 - £4,500

How to keep BNG cheap

Convert from a hardstanding or arable baseline (low score, easier to beat) rather than from a meadow or hedgerow (high score, harder). Provide on-site delivery rather than buying units. Hold a hedgerow rather than replacing it.

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Reviewed for build by O. Wakefield-Smith, Digital Signet research, Q2 2026. A chartered surveyor (RICS MRICS) sign-off is being procured for the live site. Statutory and tax figures bracket their published ONS, gov.uk or HMRC source on the page where they appear; the £/m² build-cost bands are the site's own indicative model, not a published dataset.