Single storey rear extension permitted development rules in England

The standard PD limits for rear extensions

Planning Portal guidance summarises PD rules for common projects like single-storey extensions, and government technical guidance explains how the GPDO is structured (Part 1, Class A for extensions).

For larger home extension prior approval guidance, the Planning Portal states the 'general' position: detached houses up to 4m beyond the rear wall of the original house; other houses up to 3m beyond the rear wall of the original house.

Other PD limits still apply—height, materials in some contexts, and coverage limits—so check the full Class A conditions before building.

The larger home extension prior approval route (6m/8m)

The Planning Portal application-type guidance explains the 'larger home extension' route: where not on Article 2(3) land or in an SSSI, the rear extension depth limit increases to 8m for detached houses and 6m for other houses.

Key procedural points you must follow:

• You must submit a Prior Approval: Larger Home Extension application before starting; it cannot be done retrospectively.
• The LPA serves notice on adjoining owners/occupiers and must give neighbours at least 21 days to make objections.
• The notice sets out the 42-day determination period end date.
• If the authority does not notify its decision within that period, the development may go ahead (subject to complying with all other PD rules).

When permission is usually required

You should assume you likely need planning permission (or at least cannot rely on PD) if:

• You're on Article 2(3) land (conservation area, AONB, National Park, World Heritage Site, etc.) and the relevant PD right is restricted
• PD rights have been removed by an Article 4 direction or a condition on your property's original permission
• The proposal doesn't meet Class A limitations/conditions (height, position, etc.)

Common expensive mistakes

These mistakes routinely cause costly rework or enforcement:

• Starting work before prior approval is granted (or the 42-day window ends). The Planning Portal guidance is explicit that prior approval cannot be retrospective.
• Using the wrong baseline: 'original house' is defined by reference to the house as first built or on 1 July 1948 (if built before). Extensions added after that date don't count toward your PD allowance.
• Ignoring designated land limits and assuming 'it's just an extension.' Article 2(3) land has tighter rules.

Real-world costs and timelines

Prior approval fee: The larger home extension prior approval typically costs around £96 (check current Planning Portal fees).

Full householder application: If you need planning permission, expect around £258 for a typical householder application (subject to annual indexation from April 2025).

LDC for proof: An LDC for proposed works costs around £129 (half the full householder fee) and provides formal certainty—useful for resale.

Timeline: Prior approval has a 42-day determination period. Full planning applications are decided within 8 weeks (13 weeks for unusually large/complex).

Step-by-step: what to do next

Follow this workflow to avoid expensive rework:

• Confirm eligibility: house type (not flat), removed PD rights, designated areas
• Measure from the 'original house' and prepare accurate plans
• Decide route: standard PD, larger home extension prior approval, or full householder planning permission
• Consider an LDC for proof even where you believe it's PD (useful for resale)
• Use PlanWiser's Planning Advisor, Property Checker, and Mock Application tools to validate before building