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Section 106, CIL and BNG

Section 106 obligations, Community Infrastructure Levy and 10 percent Biodiversity Net Gain sit between build cost and contingency in the appraisal. CIL is per sqm of net additional floorspace; s106 is per-scheme; BNG is per habitat unit. Always model these separately, not as a percentage of GDV.

When CIL applies vs Section 106

  • CIL is a tariff-style charge calculated as £/sqm of net additional floorspace.
  • Section 106 covers site-specific obligations (affordable housing, infrastructure, contributions).
  • Both can apply on the same scheme but a CIL R123 list (now historical) used to bar double-charging for the same item.

BNG 10 percent requirement

  • Statutory BNG in force from 12 Feb 2024 (major sites) and 2 Apr 2024 (small sites).
  • From 6 Aug 2026 a new exemption covers sites up to 0.2ha with no on-site priority habitat; the self-build and custom-build exemption is removed (retained only for applications submitted before 6 Aug 2026).
  • Schemes must deliver 10 percent net gain in biodiversity units against a baseline.
  • Off-site units price varies; statutory biodiversity credits from Natural England run from £42,000 per unit (tier A1, the cheapest) to £650,000 (tier A5), priced as a deliberate last resort.

How CIL is calculated

CIL liability = (chargeable area in sqm) x (council CIL rate £/sqm) x (BCIS All-In Tender Price Index ratio between adoption and grant of planning).

Small-sites CIL relief

Schemes that fall below CIL minimums (100 sqm net additional floorspace, 1 dwelling) qualify for self-build relief or minor-development relief. Always check the council's adopted CIL charging schedule.

Community Infrastructure Levy· Current statutory regimeAppraisal model reviewed by Oliver Wakefield-Smith (data integrity) with chartered-surveyor (MRICS) and CTA tax review. No affiliate links.