CIL liability by floorspace and residential exemptions
CIL is charged on net additional floorspace, and the residential exemptions are lost more often through paperwork than through eligibility. Here is the sequence to follow.
The Community Infrastructure Levy is charged per square metre of net additional gross internal floorspace, at the rate in the charging authority's adopted schedule, indexed to the year the permission was granted. It is not discretionary, it is not negotiable, and unlike a section 106 obligation it does not respond to a viability argument on an individual scheme.
For a self-builder the numbers can be alarming and the exemptions are generous. What catches people is the procedure. The self-build and residential exemptions are lost through missed paperwork far more often than through failing to qualify.
How the charge is calculated
Take the gross internal area of the new build, deduct any qualifying existing floorspace, multiply by the rate in the charging schedule for that use and that zone, and apply the index.
Three parts of that need care.
Gross internal area is measured to the internal face of the external walls, including internal walls, stairs and integral garages. It is not the same as the floor area quoted in sales particulars, and it is not the same as the figure on the application form if that was measured differently.
Existing floorspace can only be deducted where the building has been in lawful use for a continuous period of at least six months within a defined preceding period. A barn that has stood empty for a decade brings no deduction, which is why conversion schemes on long-derelict buildings sometimes carry a levy the applicant never expected.
Indexation applies. The published rate in the charging schedule is a base figure, and the amount payable is adjusted using the index for the relevant year. Ask the authority for the current figure rather than reading the schedule alone.
The floorspace threshold and new dwellings
Development of less than 100 m² of new build floorspace is generally exempt as minor development. That exemption falls away the moment the development creates a dwelling. A 62 m² annexe that qualifies as a separate dwelling is chargeable in full, while a 95 m² extension to an existing house is not chargeable at all.
Where a scheme replaces a building, the existing floorspace deduction usually does most of the work. Where it adds an entirely new unit on a garden plot, expect the full charge on the whole gross internal area.
Buildings into which people do not normally go, and structures below the threshold that create no dwelling, sit outside the levy.
Self-build exemption
Anyone building their own home, or commissioning it, can claim exemption from CIL provided they own the property and occupy it as their sole or main residence for three years from completion.
The sequence matters more than the substance.
- Submit the assumption of liability form.
- Submit the self-build exemption claim and receive the authority's written grant of exemption.
- Only then submit the notice of the intended start date, which the regulations call a commencement notice.
- Only then start work.
- Within the period allowed after completion, submit the second part of the claim with the evidence required, which typically includes the building regulations completion certificate, proof of occupation such as a council tax bill, and evidence of title or a self-build warranty.
Starting work before the exemption is granted, or before the start-date notice is served, is where claims fail. The regulations in this area have been amended and the consequence may be a surcharge rather than total loss of relief, so check the current position with the charging authority. Either way, serve the notice.
The three-year clawback is real. Selling or letting the property within three years of completion triggers repayment, and the authority checks.
Extension and annexe exemptions
Two further exemptions apply to work at your own home.
An extension of 100 m² or more to a dwelling you own and occupy as your principal residence can be exempted, provided the extension does not create a new dwelling. Below 100 m², the minor development rule already means no charge.
A residential annexe within the curtilage of your main dwelling can be exempted, again provided you own and occupy the main dwelling as your principal residence. The annexe is subject to a three-year restriction on separate sale or letting, so an annexe built as a rental unit does not qualify.
Both are claimed before work starts and both require the same discipline about the assumption of liability and the start-date notice.
Note the interaction with planning policy. An annexe exempted from CIL as ancillary accommodation is an annexe for planning purposes too, and if it is later occupied as an independent dwelling that is a breach of both the exemption and, usually, a planning condition.
What losing an exemption looks like
A claim that fails does not simply revert to the ordinary charge. The authority issues a demand notice, and surcharges can be added for failure to assume liability, for failure to serve the start-date notice, and for late payment. Interest runs. In serious cases the authority can serve a CIL stop notice preventing further work until payment is made.
That is a substantially worse position than the levy alone, and it arrives after the money has been spent on the build.
Where a levy is unexpectedly charged on a scheme that also carries policy obligations, the Affordable Housing Statement and any section 106 heads of terms should be reviewed together, because paying twice for the same infrastructure is a point the regulations already address and worth raising if it appears to have happened.
Challenging a liability notice
There is a structured route, and it has short deadlines.
Start with a request to the charging authority to review the chargeable amount, which has to be made within a set period after the liability notice is issued. If the review does not resolve it, there is an appeal to the Valuation Office Agency on the calculation of the chargeable amount, and separate appeal routes for apportionment between owners, for charitable and social housing relief decisions, for surcharges and for the deemed date on which development is treated as having started.
Appeals about the rate itself are not available. The charging schedule was examined when it was adopted, and the appeal routes go to how the schedule was applied to your development, not to whether the rate is fair.
Get the floor areas checked before appealing. Most successful challenges turn on measurement or on an existing floorspace deduction the authority did not apply, rather than on a point of principle.
A practical sequence for a self-build
Illustrative example: a plot with an existing garage, permission for a 180 m² house. The applicant assumes liability, claims self-build exemption and receives written confirmation, serves the start-date notice the week before groundworks, and files the evidence within the period allowed after the building regulations completion certificate is issued. No levy is payable. Had the digger arrived a week earlier, the position would have been very different.
Budget the levy in full at the outset anyway. An exemption you have not yet been granted is not a saving, and a scheme that only works if the exemption is granted is a scheme with one point of failure.
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This is general guidance, not legal advice; CIL rates and procedures vary by charging authority and the regulations are amended from time to time, so check the current position with the charging authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.
Frequently asked questions
How is CIL calculated?
On net additional gross internal floorspace, multiplied by the rate in the charging authority's adopted schedule for that use and zone, then adjusted by the published index for the relevant year. Existing floorspace can be deducted only where the building has been in lawful use for a continuous period of at least six months within a defined preceding period.
Is there a 100 m² threshold?
Yes for development that creates no dwelling. New build of less than 100 m² is generally exempt as minor development. That exemption does not apply where the scheme creates one or more dwellings, so a small new house or a self-contained unit is chargeable on its whole floor area regardless of size.
Who qualifies for the self-build exemption?
Someone building their own home, or commissioning it from a builder or contractor, who owns the property and occupies it as their sole or main residence for three years from completion. Selling or letting within that period triggers repayment. The exemption must be claimed and granted before work starts.
What happens if I start work before serving the notice?
You risk the exemption and you risk surcharges. The regulations require the assumption of liability, the granted exemption and the notice of the intended start date to be in place before development begins. The consequences have been amended over time, so confirm the current position with the charging authority, and serve the notice regardless.
Can I appeal a CIL liability notice?
You can request a review of the chargeable amount by the charging authority within a short period after the notice is issued, and then appeal to the Valuation Office Agency on the calculation. Separate routes cover apportionment, relief decisions, surcharges and the deemed start date. You cannot appeal the rate itself.
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.