Most conservatories fall under a specific minor development exemption from the Community Infrastructure Levy — but the exemption isn’t automatic, and losing it by combining works or missing a form can turn a straightforward extension into an unexpectedly expensive one.

What the Community Infrastructure Levy actually is

The Community Infrastructure Levy (CIL) is a charge that local authorities in England and Wales can choose to apply to new development, used to help fund local infrastructure such as roads, schools and green space. Not every council charges CIL, and where it is charged, the rate and rules are set out in that specific authority’s own charging schedule — there is no single flat national rate, which is why checking locally, rather than assuming a figure from elsewhere applies, matters.

The minor development exemption most conservatories fall under

Government guidance is explicit that residential extensions under 100 square metres, which are not part of a development creating a new dwelling, are already exempt from the levy under the minor development exemption. The overwhelming majority of domestic conservatories sit comfortably under this threshold, meaning most homeowners building a conservatory as a standalone extension to an existing house will not face a CIL charge at all.

Where a conservatory can lose that exemption

The exemption is tied to the nature of the development, not simply the physical size of the conservatory in isolation. Guidance specifically notes that a structure can become liable if it forms part of a wider development that also creates a new dwelling, or contributes to a project’s net additional floor space reaching 100 square metres or more when combined with other works. In practice, this matters most where a conservatory is being built as one part of a larger scheme — for example, alongside a loft conversion, a garage conversion, or another extension on the same property — since it’s the combined additional floor space across the whole scheme that’s assessed, not the conservatory alone in isolation from everything else being built.

Checking your council’s charging schedule before you design

Because CIL is set locally, and some council areas don’t charge it at all, the practical first step is checking your own local planning authority’s current charging schedule, rather than assuming either that CIL definitely won’t apply (because most conservatories are exempt) or that it definitely will. This is a genuinely different question from planning permission itself — a project can be entirely permitted development, requiring no planning application at all, and still, in principle, be a development that needs a CIL exemption claim if it’s large enough or combined with other works.

Why the paperwork matters even when you’re confident you’re exempt

A recurring, costly mistake in CIL cases generally is assuming an exemption applies automatically because a project is small, without actually submitting the required exemption claim form to the local authority before starting work. CIL exemptions typically need to be formally claimed and confirmed in writing before development begins — starting work without that confirmation in place, even for a project that would genuinely have qualified, can in some circumstances result in the exemption being lost and the full levy becoming payable. This is a case where the process, not just the underlying facts, determines the outcome, so checking the exact procedure with your local planning authority before work starts is worth the (usually free) time it takes.

FAQs

Do I need to do anything if my conservatory is clearly under 100 square metres and stands alone?

Even where you’re confident the minor development exemption applies, it’s worth confirming directly with your local planning authority whether any formal notification or claim is expected before work starts, since local process can vary.

Does CIL apply on top of planning permission fees?

Where it applies, CIL is a separate charge from the planning application fee itself, and from any Building Regulations fees — it’s specifically an infrastructure levy, assessed and charged independently of those other costs.

Do all councils in England charge CIL?

No. It’s a local choice, and coverage varies — some authorities charge it, others don’t, which is why checking your own council’s specific charging schedule is the only reliable way to know your local position.

Sources

This guide draws on the following primary sources, current as of 16 September 2026:

• gov.uk: Community Infrastructure Levy — guidance

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Compare Conservatories is an independent guide. We may earn a fee from some links; this never affects what we write. This article is general information, not legal advice on any specific property — always confirm with your Local Planning Authority.