8 planning constraints that could block your extension

Can you extend? Check permitted development and the rules on your street before you call an architect. Check a site free shows your council, whether you are in a conservation area, and a basic flood check, with no signup.

In many cases you can extend a house without a planning application. This is called permitted development. But several constraints can remove or restrict those rights, so even a modest extension needs a formal application. Wales and Scotland have their own permitted development rules, so this guide is about England.

Here are eight constraints that could affect your plans, with the official source for each.

1. Conservation area

Impact on extensions: conservation areas are "Article 2(3) land", so permitted development is reduced. Side extensions need planning permission. A single-storey rear extension can still be permitted development within the standard limits, but the larger home extension scheme (the 6 m and 8 m prior approval route) is not available, and any rear extension of more than one storey needs permission. You cannot add cladding, and roof extensions such as dormers need permission. Design and materials are scrutinised more closely.

How to check: check a site free shows whether the point is in a conservation area. Your council's website holds the boundary map and the appraisal. See how to check if a property is in a conservation area.

2. Listed building status

Impact on extensions: if your home is listed, you need listed building consent for any alteration, inside or out, in addition to any planning permission. Even minor changes such as replacing windows, moving a partition wall or adding a satellite dish can need consent.

How to check: search the National Heritage List for England, or open the £9.99 site report, which includes the listed building check with the grade and source.

3. Article 4 direction

Impact on extensions: an Article 4 direction removes specific permitted development rights in a defined area. The scope varies. Some directions remove rights for extensions, others target changes of use or alterations to frontages. You need to know what the specific direction covers. In England, a planning fee is usually payable for an application a direction brings into control.

How to check: the site report includes the Article 4 check where the council's data is published, and lists the permitted development classes removed where the data records them. England's Article 4 data depends on each council's submissions, so ask your council as well. See how to check for an Article 4 direction.

4. Green belt

Impact on extensions: extensions to existing buildings in the green belt can be acceptable provided they are not disproportionate to the original building, as it stood on 1 July 1948 or as built if later. What counts as disproportionate is a judgement and varies between councils. Some publish a percentage guide, so look at your council's policy before you design anything large.

How to check: the site report includes the green belt check. Your council's local plan policies map is the version used for decisions.

5. Flood zone

Impact on extensions: an extension in Flood Zone 2 or 3 needs a flood risk assessment, but for a householder extension or a non-domestic extension of up to 250 square metres the Environment Agency's standing advice sets out what it must cover. It asks for floor levels at least 600 mm above the estimated flood level, or extra flood resistance and resilience measures where that is not possible. A householder extension does not have to pass the Sequential Test.

How to check: check a site free includes a basic river and sea flood check. The site report adds the classification and source. The Environment Agency's own Flood Map for Planning is the official view for England, and the one our checker reads.

6. Tree preservation orders

Impact on extensions: if a tree near your proposed extension has a TPO, you cannot remove, prune or damage it without the council's written consent. The tree's root protection area, a circle with a radius of about 12 times the trunk diameter under BS 5837, may limit where you can dig foundations, which can make certain extension positions impractical. Trees in a conservation area need six weeks' notice before work.

How to check: the site report includes the TPO check, but England's TPO data is incomplete because it depends on council submissions. For specific trees, ask your council's tree officer.

7. National Landscape (formerly AONB)

Impact on extensions: AONBs, now branded National Landscapes, are also Article 2(3) land, so the same restrictions apply as in conservation areas: no larger home extension scheme, side extensions need permission, and no cladding. Design quality is expected to reflect the landscape.

How to check: the site report includes the check. Natural England's MAGIC map shows the boundaries.

8. Scheduled monument

Impact on extensions: this is the rarest on the list and the most restrictive. If your property is on or next to a scheduled monument, any ground works, including foundations for an extension, that could affect archaeological remains need scheduled monument consent from the Secretary of State. It is separate from planning permission and has its own application.

How to check: the site report includes the scheduled monument check, and Historic England's National Heritage List shows the extent.

Check before you plan

The worst time to discover a constraint is after you have paid for architectural drawings. Check a site free for your council, conservation area status and a basic flood check, then decide whether the £9.99 site report is worth it for the full picture. It covers everything we can check within 500 m of your pin, for 30 days, and the report link never expires. See a sample report first if you want to see what you get.

We show what we found, what came back clear, and where a source couldn't be checked. Some councils don't publish every dataset, so ask the council where it matters. A pre-application enquiry or a lawful development certificate gives you a definite answer for your project. Discuss material findings with your architect or a planning consultant before you finalise your design.