Planning
Planning permission for house extensions
The first question, and the one that decides everything else. Many extensions need no planning application at all — but the limits are specific, and they are not the same for a terrace, a semi and a detached house.
Of the homeowners who told our quote tool where they were up to over the last 90 days, around a quarter did not know whether they needed planning permission, and most had no drawings yet. If that is you, nothing here assumes prior knowledge.
Start with these
Do I need planning permission?The depth, height and coverage limits, by property type.Read more →Building RegulationsWhat Building Control checks, and the two approval routes.Read more →
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Get free quotesWritten and checked by the HouseExtensionExpert editorial team · Last updated: 31 August 2026 · Planning and Building Regulations points are checked against current Planning Portal and GOV.UK guidance; cost ranges come from BestBuilders’ 2026 regional cost model (published national cost guides × a regional labour index, averaged across 519 UK towns). Ranges are indicative, not quotes.Next scheduled review: November 2026 · Spotted something out of date? Tell us.