The Community Infrastructure Levy, or CIL, is a development charge used by authorities that have adopted a charging schedule. Whether you pay depends on the applicable schedule, the development and any valid exemption or relief. Planning permission alone does not settle the CIL paperwork.
This guide covers England. Check the collecting authority's current documents for your site; there is no single national residential rate.
Establish the charge before relying on an exemption
Ask which charging schedules apply, the relevant zone and development category, and the indexed rate. In London, Mayoral CIL may need checking alongside a borough levy. Keep CIL separate from the planning application fee and any section 106 obligation. The government's CIL guidance explains the framework.
A useful initial file contains the permission or proposed application, existing and proposed floor areas, use information and evidence concerning any existing floorspace claimed in the calculation. Do not assume that every building proposed for demolition creates a deduction: the calculation rules and lawful-use evidence matter.
Ask for clarification where the liability notice differs from your estimate. It is easier to resolve a measurement or use issue while the supporting plans and records are assembled than after the construction programme assumes a particular bill.
The under-100-square-metre rule has a new-dwelling exception
Regulation 42 generally exempts minor development where the gross internal area of new build is less than 100 square metres. The exemption does not apply where the development comprises one or more dwellings.
A small new house can therefore be liable even when below 100 square metres. An extension below that threshold, forming no new dwelling, is a different case. “Under 100” also means less than 100, not 100 or below.
Treat the floorspace calculation and the proposed use as two separate checks. Calling a building an annex on a drawing does not settle whether it comprises a dwelling for CIL purposes.
Residential extensions and annexes have distinct exemptions
The claimed exemptions in regulation 42A concern a person with the required material interest in their principal residence:
- A residential extension enlarges that residence without creating an additional dwelling.
- A residential annex is within its curtilage and comprises one new dwelling.
A qualifying larger extension can therefore use the residential-extension exemption even where the minor-development exemption is unavailable. A separate new home elsewhere on a site should not be assumed to qualify as an annex; test the actual requirements.
Self-build housing has another relief route with its own evidence and procedures. Do not use a self-build form as a substitute for identifying whether the development is an extension, annex or new house. A BNG exemption also says nothing about CIL: these are separate regimes.
Get the claim decided before starting
Under regulation 42B, the normal extension or annex claim must reach the collecting authority before commencement. Starting before notification of the decision causes the claim to lapse, subject to the regulation's specific provisions for changes to already-exempt development.
Submit the correct claim and evidence, obtain the written decision and keep it with the permission. For construction planning, identify what counts as commencement and tell the contractor which pre-start steps remain outstanding. Booking a contractor does not complete an exemption claim.
Does every exempt project need a commencement notice?
No. Regulation 67(1A) excludes a development where no CIL is payable because the residential-extension exemption was granted. It also contains exceptions for regulation 42 development and a zero chargeable amount.
A residential-annex exemption is different: the commencement-notice requirement applies. Under the current English guidance, missing that notice can result in a surcharge. Do not turn “claim before starting” into an inaccurate blanket statement that every exempt extension needs Form 6. The government addresses this distinction in CIL guidance paragraphs 050 and 053.
Where notice is required, regulation 67 requires it no later than the day before commencement. Keep the authority's acknowledgement and ensure the intended start date matches the actual programme.
Annexes carry continuing conditions
Annex exemption can be withdrawn following specified events within the three-year clawback period, including letting the annex or selling it separately from the main residence. Changes to the main residence can also matter. Regulation 42C sets out the events and notification duty.
Consider the intended occupation and any sale plans before relying on relief. If circumstances change, check the duty to notify rather than assuming that completion ended all obligations.
Worked example: two projects of similar size
Imagine a 75-square-metre addition enlarging an existing home without creating a dwelling, and a separate 75-square-metre new home. The first may fall within the minor-development exemption. The second cannot rely on its size alone because of the dwelling exception.
Now imagine a 115-square-metre extension to the owner's principal residence. It needs assessment for the claimed extension exemption, including the ownership and use criteria and pre-start decision. Its larger size does not automatically mean CIL is payable, but the correct procedure matters.
Sources and review
The linked CIL Regulations and government practice guidance were compared on 8 September 2026 with automated research assistance. This source check is not professional confirmation of liability or relief. Rates, floor areas, ownership, occupation and permission history must be checked for the actual project.