Chargeable development: what CIL is calculated on
The Community Infrastructure Levy is calculated on new gross internal area, less the floorspace of buildings that pass the in-use test. Here is how the measurement, the deductions and the liability notice actually work.
CIL is calculated on new gross internal floorspace, not on the value of a scheme or the area of the site. Under the Community Infrastructure Levy Regulations 2010, the CIL chargeable development is the development permitted by the planning permission, and the levy bites when that permission creates 100 m2 or more of new build gross internal area, or creates one or more dwellings at any size at all. Everything after that is a deduction argument: what already stands on the land, whether it has been in lawful use recently enough to count, and whether relief applies.
Get the floorspace schedule right at application stage and the rest usually follows. Get it wrong and you find out through a liability notice carrying a number nobody on the project budgeted for.
What makes a development chargeable
Only a charging authority with an adopted charging schedule collects the levy, so the first check is whether the council has one and which rate band covers the site. Rates are set per square metre, by use and often by geographical zone within the district. Where no schedule has been adopted, contributions come through section 106 instead.
Regulation 42 removes liability where the chargeable development creates less than 100 m2 of new build gross internal area. The exception swallows much of the comfort. If the development comprises one or more dwellings, that 100 m2 floor does not apply at all, so a 62 m2 annexe forming a separate dwelling is chargeable while a 62 m2 kitchen extension to the same house is not.
A change of use on its own usually produces no chargeable floorspace, because nothing new is built. Liability arrives when the conversion works add floorspace, or when the existing building fails the in-use test and its area cannot be set against the new. That line between operational development and a material change of use under section 55 does more work in a CIL calculation than most applicants expect.
How gross internal area is measured
Gross internal area is measured to the internal face of the external enclosing walls, floor by floor, and it takes in a great deal more than the habitable rooms. Internal walls and partitions, columns, chimney breasts, stairwells and lift shafts, corridors, WCs, plant rooms, integral garages and service voids above floor level all count towards the figure.
What falls outside is narrower than people hope.
| Counted in gross internal area | Left out |
|---|---|
| Integral garage with doors and four walls | Open sided car port |
| Enclosed internal plant or tank room above floor level | Perimeter wall thickness and external projections |
| Stairwell and landing at every floor level | External open sided balconies and fire escapes |
| Atrium, entrance hall and internal corridors | Canopies and covered ways |
| Conservatory forming part of the building | Detached garden store in a residential curtilage |
Most charging authorities follow the measurement conventions in the RICS code of measuring practice, and many publish a short note confirming that. Check the council's own CIL page before you submit, because the additional information form asks for existing and proposed areas separately and the officer will measure against your drawings.
Deducting floorspace that already exists
The chargeable amount under regulation 40 is not the new floorspace figure. It is the new gross internal area less the area of any retained parts of in-use buildings, less the area of buildings that are to be demolished, where those buildings qualify. Two conditions sit behind that deduction, and both are regularly missed.
The building has to be a relevant building, meaning one standing on the relevant land on the day planning permission first permits the chargeable development. Demolish early to tidy the site before the decision and the deduction goes with the rubble. And the regulations exclude buildings into which people do not normally go, or go only intermittently to inspect or maintain fixed plant, which is why an unmanned agricultural or utility structure often brings nothing to the calculation.
For a full permission, the day planning permission first permits the development is the grant date. For an outline permission it is the final approval of the last reserved matter, and where the scheme is phased each phase is treated as a separate chargeable development with its own notice.
The in-use building test
A relevant building only produces a deduction if it is an in-use building. The regulations define that as a building containing a part that has been in lawful use for a continuous period of at least six months within the three years ending on the day planning permission first permits the chargeable development.
Read that carefully. Six months has to be continuous, not cumulative. The three-year window closes on the permission date, not on the date you bought the site. The use has to have been lawful, so an unauthorised use that has not become immune from enforcement earns nothing.
A long vacant building is the classic loss. A mill or office block empty for four years converts to flats with no deduction at all, and the whole of the new floorspace is chargeable. That single point can move a scheme's levy bill by a six-figure sum, which is why the occupation evidence should be assembled before the application goes in rather than after the notice arrives.
Useful evidence includes business rates or council tax records, utility accounts showing consumption rather than standing charges, signed leases with rent receipts, VAT returns, dated photographs and staff or delivery records. Collecting authorities vary in what satisfies them. A short occupation schedule with the documents appended, submitted with the CIL additional information form, saves an argument later.
Mezzanines, plant and ancillary space
Inserting a mezzanine into an existing building is development in its own right where the building is in retail use and the new floor exceeds 200 m2, under section 55(2A) of the Town and Country Planning Act 1990. Where permission is needed and granted, that mezzanine is new gross internal area and it is chargeable. Below the threshold, and outside retail use, the works may not be development at all, in which case no chargeable development arises.
Basements count in full. So do enclosed bin stores, cycle stores and substations built as part of the scheme, unless the people-do-not-normally-go exclusion applies to them. Roof plant screened but not enclosed is generally out.
Illustrative example: a permission converts a 400 m2 building, vacant for five years, and adds a 150 m2 rear wing. Because the building fails the in-use test, no deduction is available and the net chargeable area is 550 m2 rather than the 150 m2 the applicant had budgeted. The figures here are illustrative only and are not drawn from a real scheme.
Reading the liability notice and checking the figure
The collecting authority issues a liability notice as soon as practicable after permission first permits the development. It sets out the chargeable amount, the rates and index applied, and the person or people liable. Rates are indexed annually, so the figure on a notice issued this year will not match the raw rate in a schedule adopted some years ago.
Three things then have to happen in order, and the sequence is unforgiving. Someone assumes liability on the correct form. Relief or exemption is applied for and granted in writing. A commencement notice is served before any material operation starts on site.
- Check the measured areas against your own floor-by-floor schedule.
- Check whether every existing building has been credited, and if not, why not.
- If the calculation looks wrong, request a review by the collecting authority within 28 days of the liability notice under regulation 113.
- If the review does not resolve it, appeal the chargeable amount to the Valuation Office Agency under regulation 114 within 60 days of the review decision.
Miss the commencement notice and self-build or annexe relief can fall away entirely, with a surcharge on top. Deadlines here are hard, and collecting authorities have limited discretion to forgive a late form. Between 15 and 25 per cent of receipts pass to the parish or town council, the higher figure applying where a made neighbourhood plan covers the area, which is one practical reason to know whether a neighbourhood plan applies to your site.
If you are assembling the application pack alongside the CIL forms, the full list of supporting report types shows what else the validation checklist is likely to ask for, and you can enter a postcode on PlanScope to see which of them a particular site is likely to need. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.
This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it.
Frequently asked questions
Is a change of use chargeable under CIL?
A change of use with no new build floorspace normally produces nothing to charge, because the levy is calculated on new gross internal area. Liability appears when conversion works add floorspace, or when the existing building fails the in-use test so its area cannot be deducted. Check the charging schedule, because rates are set by use as well as by zone.
Does an extension under 100 m2 escape CIL?
Regulation 42 removes liability where the chargeable development creates less than 100 m2 of new build gross internal area, but only where no new dwelling is created. A small annexe that forms a separate dwelling is chargeable at any size. A residential extension to your own home may also qualify for a separate exemption, claimed on the correct form before work starts.
What counts as proof that a building was in lawful use?
Business rates or council tax records, utility accounts showing actual consumption, signed leases with rent receipts, VAT returns, dated photographs and delivery or staff records are all used. The test is a continuous six months of lawful use within the three years ending on the day permission first permits the development. Collecting authorities differ on what satisfies them, so ask early.
Can I challenge the figure on a CIL liability notice?
Yes. Ask the collecting authority to review the calculation within 28 days of the liability notice under regulation 113, setting out where you say the measurement or the deduction is wrong. If the review does not resolve it, the chargeable amount can be appealed to the Valuation Office Agency under regulation 114 within 60 days of that review decision.
Are basements and integral garages included in the measurement?
Both are counted. Gross internal area is measured to the internal face of the external walls at every floor level, and it includes basements, integral garages with doors, plant rooms, stairwells, corridors and internal circulation. Open sided car ports, external balconies and canopies sit outside the measurement, as does the thickness of the perimeter wall itself.
When is the CIL liability actually calculated?
The chargeable amount is fixed by reference to the day planning permission first permits the chargeable development, which is the grant date for a full permission and the approval of the last reserved matter for an outline. Rates are indexed annually to that date. Phased schemes are treated as separate chargeable developments, each with its own notice.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.