Glossary
The Community Infrastructure Levy on London extensions
A charge on new floorspace, used by councils to fund infrastructure. Application-specific.
A charge on new floorspace, used by councils to fund infrastructure. Application-specific.
CIL is a charge levied by a local authority on new floorspace, calculated per square metre and index-linked. Most householder extensions are exempt because CIL is only charged on developments creating 100 m² or more of new floorspace, or a new dwelling of any size — but the exemption must be claimed before work starts.
Two triggers matter to a homeowner. The first is creating 100 m² or more of new internal floorspace — reached by a large wraparound plus loft, or by a basement. The second is creating any new dwelling, including an annexe treated as separate accommodation or a garden building converted to a self-contained unit.
In London there are usually two charges: the borough's own CIL and the Mayoral CIL that funds Crossrail. Both are index-linked from the year the charging schedule was adopted, so the rate quoted in the schedule is not the rate paid.
The sequence is unforgiving. Assume liability, submit the exemption claim, receive the authority's acknowledgement, then submit a commencement notice — all before any work starts. Starting work before the commencement notice is acknowledged loses the exemption entirely and triggers surcharges.
The exemption is then held for three years, during which the property must remain the owner's principal residence. Selling inside that window claws the charge back.
Existing floorspace in lawful use for at least six of the previous three years is deducted from the chargeable area, which is why demolishing and rebuilding is often less costly under CIL than it first appears.
A worked Barnet example of community infrastructure levy (cil): with 20 conservation areas — the Hampstead Garden Suburb Conservation Area and the Mill Hill Conservation Area among the best known — London Borough of Barnet (Barnet Council) sees community infrastructure levy (cil) constantly, and there is no borough-wide Article 4 direction, so permitted development generally survives outside conservation areas. Where community infrastructure levy (cil) pushes a Barnet scheme out of permitted development, the route becomes a £548 application decided in 8 weeks rather than a £249 prior approval in 6 weeks.
| Charged on | New floorspace, per m², index-linked |
|---|---|
| Householder threshold | 100 m² of new floorspace |
| New dwelling | Chargeable at any size |
| London | Borough CIL plus Mayoral CIL |
| Self-build exemption | Claim and commencement notice before starting |
| Clawback period | 3 years as principal residence |
Only if it creates 100 m² or more of new floorspace, or a new dwelling.
The exemption is lost and surcharges apply. The sequence is strict.
No. Unlike a section 106 agreement, CIL is a formula, not a negotiation.
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