Free tool
Permitted development checker
Answer a few questions about a single-storey rear or side extension to get an indicative result, based on the current GPDO 2015 rules.
Most single-storey rear extensions fall under permitted development if they project no more than 4m (detached houses) or 3m (semi-detached and terraced houses) beyond the original rear wall, stay under 4m in height, and meet a handful of other conditions. This tool checks your specific figures against those rules and cites the exact one that decided the result.
Common questions
FAQs
Is this checker legally binding?
No. It's indicative guidance based on the standard Class A permitted development rules, not legal advice, and it can't account for every site-specific factor. For certainty, apply to your council for a Lawful Development Certificate.
What if my extension doesn't fit the rear or side categories here?
This tool covers single-storey rear and side house extensions only, the highest-volume case. Loft conversions, outbuildings and garden rooms sit under different permitted development classes — get in touch and we'll help you understand what applies.
What's an Article 4 direction?
A local rule that removes some permitted development rights on specific streets or in specific conservation areas. It varies within a borough, not across the whole of it, so always check your own property against your council's planning register.
Want to understand the full picture, not just this one rule? Read our planning permission guide →
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