Permitted development rights for householder extensions apply only to houses, not flats or maisonettes — so a conservatory on a flat needs full planning permission, plus separate consent under the lease.

This article covers permitted development rules in England. Scotland, Wales and Northern Ireland run separate planning systems with their own rules – check the equivalent local guidance if you’re outside England. This is general information, not planning advice for your specific property.

The short answer: permitted development rights for extensions don’t apply to flats

This catches a genuine number of flat and maisonette owners out, because it’s easy to assume that if a conservatory of a certain size is fine without planning permission on a house next door, the same rule applies to your flat. It doesn’t. Permitted development rights for householder extensions – the rules that let many house owners add a conservatory without a full planning application, provided it meets size and design limits – are set out under the Town and Country Planning (General Permitted Development) Order 2015, and they apply specifically to a “dwellinghouse.” Flats and maisonettes are explicitly excluded from this class of permitted development rights, regardless of size, design, or how modest the proposed conservatory is.

Why the distinction exists

The legal reasoning isn’t really about size – it’s about the fact that a flat or maisonette is one unit within a building that’s shared, structurally or otherwise, with other homes. Alterations to one flat can have knock-on effects for the building as a whole and for other residents in a way that’s treated differently in planning law from a standalone house on its own plot. As a result, there is no permitted development route for a conservatory extension to a flat – you need to apply for full planning permission from your local planning authority, and the application will be assessed on its own merits against normal planning policy, without the benefit of an automatic exemption for smaller-scale work.

Does having your own garden change anything?

No. A common assumption is that a ground-floor flat with its own private garden should be treated more like a house for these purposes. It isn’t – what matters legally is whether the property is a flat or maisonette (typically meaning it’s part of a building containing more than one home, however the ownership or garden arrangements are set out), not whether it happens to have direct garden access. If your property is legally a flat, the permitted development exclusion applies regardless of what outside space comes with it.

There’s a second consent hurdle too: your lease

Planning permission is only one part of what you need. Most flats are held on a leasehold basis, and the lease itself very often requires you to get the landlord’s or freeholder’s written consent before making any structural alteration to the property or the building – a requirement that exists entirely separately from planning law. Getting planning permission from the council does not automatically give you permission under your lease, and vice versa. Check your specific lease terms and speak to your freeholder or managing agent early, ideally before you spend money on drawings or a planning application, since a lease restriction can rule out a project that would otherwise be planning-permissible.

What about maisonettes specifically?

A maisonette is generally treated the same way as a flat for these purposes if it doesn’t meet the legal definition of a self-contained “dwellinghouse” – broadly, if it shares any part of the building’s structure with another separate home. Whether a specific property counts as a dwellinghouse or not can occasionally be a genuine grey area depending on exactly how it was built and divided, so if you’re unsure, it’s worth checking directly with your local planning authority or a planning consultant before assuming either way.

What to do instead

• Assume you need full planning permission for a conservatory or extension on a flat or maisonette, rather than checking permitted development limits designed for houses;
• Check your lease for any requirement to get freeholder or landlord consent, separately from planning permission;
• If you’re unsure whether your property legally counts as a dwellinghouse or a flat, ask your local planning authority directly before committing to design work;
• Speak to neighbours or other leaseholders in the building early – alterations to one flat in a shared building are more likely to attract objections than the same work on a standalone house.

What if you’re buying a flat with an existing, unauthorised conservatory?

This is a genuinely common scenario worth being alert to: a previous owner of a flat may have added a conservatory or similar structure without realising permitted development rights didn’t apply, or without realising planning permission was required at all. If you’re buying a flat with an existing conservatory-style structure, your conveyancing solicitor should check whether planning permission was actually obtained, since an unauthorised structure on a flat carries the same enforcement risk as it would anywhere else – and potentially an additional complication if it also breaches the terms of the lease, which is a separate issue from the planning position entirely.

Talk to the freeholder and other leaseholders early

Because a flat sits within a shared building, changes to one unit are often more visible, and more likely to affect other residents, than an equivalent change to a standalone house. Beyond the formal consent requirements, it’s generally worth talking to your freeholder or managing agent, and where relevant your immediate neighbours in the building, before you get too far into design work – not because it’s legally required, but because objections from within the building can complicate both the leasehold consent process and any planning application, and an early, informal conversation can surface concerns while they’re still easy to address.

FAQs

If my ground-floor flat has its own private garden, does that change the permitted development rules?

No. What matters legally is whether the property is a flat or maisonette, not whether it has direct garden access – if your property is legally a flat, the permitted development exclusion applies regardless of what outside space comes with it.

Is planning permission the only consent I need for a conservatory on a flat?

No. Most flats are held on a leasehold basis, and the lease itself very often requires the landlord’s or freeholder’s written consent for structural alterations, separately from planning law. Getting planning permission doesn’t automatically give you permission under your lease, and vice versa.

Sources

This guide draws on the following primary sources, current as of 15 September 2026:

• Planning Portal, permitted development rights for householders – planningportal.co.uk
• Legislation.gov.uk, Town and Country Planning (General Permitted Development) Order 2015 – legislation.gov.uk
• GOV.UK, planning permission guidance – gov.uk/planning-permission-england-wales

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