Self-build exemptions across CIL and biodiversity net gain
The levy exemption turns on occupation and is claimed before work starts. The biodiversity exemption turns on scheme size and is claimed on the application. Different tests, different clocks.
Self-build gets you out of the Community Infrastructure Levy and out of mandatory biodiversity net gain, but the two exemptions have different definitions, different qualifying limits and completely different procedures. One is claimed after permission and before a spade goes in the ground, with a three-year clawback. The other is asserted on the application form and decided by the council with the permission. Confusing them is how self-builders end up with an unexpected levy bill or a biodiversity gain condition they cannot discharge.
Take them one at a time, and diary the dates.
Two exemptions, two definitions
The levy exemption in the Community Infrastructure Levy Regulations 2010 is about occupation. It is available where a person builds or commissions a dwelling and occupies it as their sole or main residence, and it is policed by a three-year clawback period after completion.
The biodiversity exemption in the Environment Act 2021 regime is about the character of the development. It applies where the development consists of no more than nine dwellings, on a site of no more than 0.5 hectares, and consists exclusively of dwellings that are self-build or custom housebuilding within the meaning of the Self-build and Custom Housebuilding Act 2015.
So a single house on a two-hectare plot can qualify for the levy exemption and fail the biodiversity one on site area. A scheme of six custom-build homes on a small site can qualify for the biodiversity exemption while individual plot purchasers each have to claim the levy exemption separately for their own dwelling.
Neither exemption touches section 106 obligations, which are negotiated and unaffected by either regime.
The levy exemption, step by step
The levy only applies where the charging authority has adopted a charging schedule, so check that first. Where it has, the sequence is unforgiving and the order matters more than the paperwork itself.
- Obtain planning permission.
- Submit an assumption of liability form before development starts.
- Submit the self-build exemption claim before development starts, and wait for the authority to grant it in writing. A claim that has not been granted is not an exemption.
- Serve the notice of works starting, which must reach the council before any material operation on site.
- Build.
- Within six months of completion, submit the supporting evidence.
Completion evidence normally means a building regulations completion certificate, proof of title, and a council tax bill showing you in occupation, plus one of three further items: an approved claim under the VAT scheme for self-builders, a specialist self-build warranty, or an approved self-build mortgage.
Then keep it. Selling or letting the dwelling within three years of completion is a disqualifying event and the levy becomes payable.
Where the levy claim goes wrong
Almost always on sequence rather than substance.
Starting on site before the exemption is granted, or before the notice of works starting is served, is the classic failure. Amendments made in 2019 softened the consequences of some procedural slips, but the position depends on which step was missed, so treat the order above as a hard rule rather than a target. Check the current regulations and your council's own guidance before assuming a missed step can be recovered.
Second most common: not understanding what counts as starting development. Digging foundations obviously counts. So can demolition, site clearance and the formation of an access, depending on the permission. If archaeological or ecological works are required by condition, get written confirmation from the authority about whether carrying them out begins development.
Third: assuming the exemption transfers. It attaches to the person and the dwelling. Selling the plot with the benefit of a granted exemption does not carry it over to the buyer, who must claim in their own right.
The biodiversity net gain exemption
The self-build and custom housebuilding exemption is one of a handful in the Schedule 7A regime, alongside the exemption for householder development and the de minimis exemption for development affecting less than 25 m2 of on-site habitat and less than five metres of on-site hedgerow.
Three conditions have to hold together: no more than nine dwellings, a site of no more than 0.5 hectares, and every dwelling being self-build or custom build. A single open-market plot in a scheme of eight self-build homes takes the whole development outside the exemption.
You claim it on the application, by stating that the exemption applies and explaining why. The authority decides, and the decision notice will indicate whether the biodiversity gain condition applies. Get this wrong and you discover it when you try to start work, because the deemed condition requires a biodiversity gain plan to be approved before development begins.
Where the exemption does not apply, plan for a Biodiversity Net Gain Assessment using the statutory metric. That is a competent person exercise under the Environment Act 2021 regime, and the gain plan needs the authority's approval before you start, so it belongs in the programme rather than at the end of it. A Preliminary Ecological Appraisal early on will tell you whether the site has anything on it worth arguing about.
Extensions, annexes and the small stuff
Householder work has its own reliefs on the levy side. Development of less than 100 m2 of new build floorspace is generally outside the levy unless it creates a new dwelling. Residential extensions and residential annexes have their own exemptions, claimed before development starts, and the annexe exemption carries its own clawback: the annexe must not be sold or let separately within three years.
On the biodiversity side, householder development is exempt outright, which is why an extension does not need a metric.
The two regimes therefore reach the same practical answer for a rear extension and diverge sharply for a new dwelling in a garden.
Illustrative example: a couple building one house on a 0.3 hectare paddock they own, in a district with an adopted charging schedule. Levy exemption available, claimed and granted before they start, with the notice of works starting served and completion evidence filed within six months. Biodiversity exemption available too, since it is one dwelling, under 0.5 hectares and self-build, and claimed on the application form. Both work. Move the same house onto a 0.7 hectare plot and the biodiversity exemption disappears while the levy exemption survives.
A combined checklist
Before you apply: confirm whether the council has a levy charging schedule, confirm the site area against the red line, and decide whether every dwelling is self-build or custom build.
On the application: claim the biodiversity exemption expressly and say why it applies, and set out the site area.
After permission and before starting: assume liability, claim the levy exemption, wait for it in writing, then serve the notice of works starting.
After completion: file the levy evidence within six months and keep occupying the house for three years.
A Planning Statement is a reasonable place to record the exemption position, because it puts the reasoning in front of the case officer rather than leaving it in a form field.
This is general guidance, not legal advice; check the position with your local planning 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
What are the size limits for the biodiversity net gain self-build exemption?
No more than nine dwellings, on a site of no more than 0.5 hectares, and the development must consist exclusively of dwellings that are self-build or custom housebuilding within the meaning of the Self-build and Custom Housebuilding Act 2015. A single open-market plot within the scheme takes the whole development outside the exemption.
Is there a site size limit for the CIL self-build exemption?
No. The levy exemption turns on the dwelling being built or commissioned by the person who then occupies it as their sole or main residence, with a three-year clawback after completion. Site area is irrelevant, which is why a house on a large plot can qualify for the levy exemption while failing the biodiversity one.
What happens if I start work before claiming the CIL exemption?
You risk losing it. The claim must be made and granted in writing before development starts, and the notice of works starting must be served before any material operation. Amendments in 2019 softened some procedural failures, but the outcome depends which step was missed, so treat the sequence as fixed and check the current regulations.
Does the exemption pass to a buyer if I sell the plot?
No. The levy exemption attaches to the person and the dwelling, so a purchaser must claim in their own right before starting work. Selling or letting the completed dwelling within three years of completion is a disqualifying event and the levy becomes payable in the ordinary way.
Do extensions need a biodiversity metric?
No. Householder development is exempt from the biodiversity gain condition outright. On the levy side, development of less than 100 m2 of new build floorspace is generally outside the charge unless it creates a new dwelling, and residential extensions and annexes have their own exemptions claimed before work starts.
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.