Hillingdon has relatively low conservation area coverage at 7%, so most streets remain eligible for permitted development when the design stays within national limits. Householder approvals in Hillingdon run at around 84% with an average decision time of 9 weeks.
A rear extension in Hillingdon can often be permitted development when it stays within size and design limits and no local constraint applies to your address. Always confirm at address level.
Rear extensions are permitted development for houses (not flats) within specific size and height limits set by the GPDO, Schedule 2, Part 1, Class A.
Read the full rear extension planning guide for the national rules and application process.
The CanUBuild checker surfaces real recent applications close to your address — approvals and refusals — so you can see what the planning officers at Hillingdon Council have approved for comparable schemes. Nearby precedent is one of the strongest signals for your own chances.
In Hillingdon, the answer depends on whether your property sits in a conservation area (7% of the borough), is listed, or falls within an Article 4 direction. Most rear extension proposals are permitted development for houses when they stay within GPDO limits and no local constraint applies. Check your exact address with the CanUBuild checker before spending on drawings.
Conservation areas in Hillingdon typically remove several permitted development freedoms. For a rear extension, the Larger Home Extension route and some external alterations do not apply, so a full householder application is usually required. Planning officers at Hillingdon Council assess conservation area proposals against the specific character appraisal for the street.
Hillingdon Council currently averages around 9 weeks for householder applications. Complex rear extension proposals — particularly those in conservation areas or on listed buildings — can take longer. Prior approval decisions for Larger Home Extensions are typically issued in 42 days.
A single-storey rear extension on a house in Hillingdon can be up to 4m deep (detached) or 3m deep (semi/terraced) under standard PD. The Larger Home Extension prior approval route extends this to 8m and 6m respectively, but is not available in conservation areas — which cover 7% of Hillingdon.
Address-level constraints and recent decisions around the corner. No drawings needed.