Do I Need Planning Permission? Permitted Development Rules for Extensions

Quick Answer: Most single-storey rear extensions under 4m deep (detached houses) or 3m deep (attached houses) are permitted development and don't need planning permission. Two-storey extensions, side extensions wider than half the original house, and any extensions in Article 4 areas, conservation areas, or AONB require a planning application. Always use the Prior Approval notification system for larger permitted development extensions (4–8m detached; 3–6m semi/terrace).

Summary

Permitted development (PD) rights allow homeowners to carry out certain building works without making a planning application. These rights are defined in the Town and Country Planning (General Permitted Development) (England) Order 2015 (GPDO) and its amendments. Understanding them correctly is essential both for builders (advising clients) and homeowners (avoiding enforcement action).

The most common permitted development question is about rear extensions. The government expanded PD rights for single-storey rear extensions in 2013, increasing the limits from 3m (attached houses) and 4m (detached houses) to 6m and 8m respectively under a Prior Approval notification system. These expanded limits were made permanent in 2019.

Permitted development rights can be removed or restricted by planning conditions, article 4 directions (covering conservation areas, national parks, and AONB), or by covenants. A Certificate of Lawful Development (CLD) from the local planning authority provides formal confirmation that works are permitted development — this is recommended before starting significant works and is required by some mortgage lenders.

Key Facts

Quick Reference Table

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Extension Type Standard PD Limit Prior Approval Limit Notes
Single-storey rear (detached) Up to 4m depth 4–8m depth (notification required) Height: max 4m; no eaves higher than existing
Single-storey rear (semi/terrace) Up to 3m depth 3–6m depth (notification required) Same height rules
Two-storey rear extension Up to 3m depth N/A — planning required beyond 3m Min. 7m from rear boundary
Single-storey side extension Half house width N/A Not on designated land
Wrap-around extension Complex — get CLD — L-shaped; side + rear; each element assessed
Porch Up to 3m² floor area, under 3m high N/A Cannot exceed 2m in height if within 2m of highway
Outbuilding/garden building Max 50% curtilage; max 2.5m at eaves if within 2m of boundary N/A Not used as main accommodation
Loft conversion (rear dormer) 40m³ volume addition (50m³ detached) N/A Not on front elevation; not in conservation area
Garage conversion Generally PD N/A Internal conversion; no external change
Designation Effect on PD Rights
Conservation Area Roof extensions on front restricted; cladding restrictions; rear extensions still permitted (but check specific area)
Area of Outstanding Natural Beauty (AONB) Rear extensions limited to 3m (semi/terrace) or 4m (detached) — standard limits only; no Prior Approval route
National Park Same as AONB
Article 4 Direction Local authority removes some or all PD rights; check with LPA
Listed Building ALL works require Listed Building Consent; no PD rights

Detailed Guidance

The Prior Approval Process for Larger Extensions

Extensions between the standard PD limit and the extended PD limit (e.g., 4–8m deep for detached houses) require Prior Approval notification — a simplified process, not a full planning application.

Process:

  1. Submit an application to the LPA with plans, description of the works, and the addresses of immediately adjoining properties
  2. The LPA notifies the immediate neighbours (not a general public consultation — just the adjoining properties)
  3. Neighbours have 21 days to respond
  4. If no valid objection, the LPA issues Prior Approval Not Required notification (or Prior Approval Granted)
  5. If objections are received on impact to amenity/light, the LPA assesses and may impose conditions or refuse
  6. Works must commence within 3 years of the Prior Approval

Fee: £120 (as of 2026).

Key point: Prior Approval is NOT planning permission. The LPA can only consider the impact on neighbouring amenity — not design, appearance, or character of the area. This is why Prior Approval is generally more straightforward than a full planning application.

What Counts as the "Original" House

PD rights are measured against the "original" dwelling — the building as it stood when first built, or as at 1 July 1948 (whichever is later). This means:

Example: A semi-detached house built with a 1m outrigger at the rear. The previous owner added a 2m extension. The original house depth was 8m; with the 1m outrigger it was 9m. The previous owner extended to 11m (2m addition). You want to extend further. Your PD allowance is 3m from the original rear wall of 9m (not counting the outrigger as original, as it was added later) — so you can extend to 12m. But 11m already exists, so only 1m additional PD is available.

This calculation often requires reviewing the planning history of the property on the LPA's planning portal.

Certificate of Lawful Development

A CLD is a formal confirmation from the LPA that a specific work is lawful (either because it doesn't need permission, or because it has planning permission). Two types:

Why get a CLD:

Cost: £100–£250 in England (LPA fee; professional fees additional if using a planning consultant or architect).

When You Cannot Use Permitted Development

Several situations remove PD rights entirely or significantly:

Designated land (conservation areas, AONB, national parks, World Heritage Sites):

Article 4 Directions: Local planning authorities can remove PD rights for specific areas using an Article 4 Direction. These are common in historic town centres and conservation areas. Check the LPA's website or contact the planning department before committing to any significant work.

Previous conditions: Planning conditions on the original permission for the house, or on a previous extension, can remove PD rights. For example, "No further extensions shall be erected without planning permission" is a common condition that removes all PD rights for extensions. Review any planning permissions on the property.

New build properties: Many new build estates have Article 4 Directions or planning conditions that restrict extensions and alterations to preserve the character of the development. Buyers are often unaware of this.

Planning Applications: When They're Needed

Full planning applications are required for works that exceed PD rights. Key points for building over the PD thresholds:

Frequently Asked Questions

Does a garage conversion need planning permission?

A straightforward internal garage conversion (no external changes, no change to the roof or external walls beyond filling the garage door opening with a window or door) is generally permitted development. However, if the property is in an area where off-street parking is in short supply, the LPA may resist the loss of the garage as parking provision through a planning condition. Check before proceeding. A CLD is strongly recommended.

My neighbour wants to extend right to our boundary — can they?

A single-storey rear extension can be built right up to the boundary with the adjoining land as long as it complies with the PD limits. They don't need your permission under planning law. However, the Party Wall Act 1996 applies if the extension involves work within 3m of your land or if it involves excavation near your foundations — see party wall for the Party Wall Act process. You can register an objection to Prior Approval for larger extensions (4–8m range) on grounds of impact on your amenity or light.

What if I've already built something without checking?

If work was completed more than 4 years ago (for operational development like extensions), the LPA generally cannot take enforcement action — this is the 4-year rule under Section 171B of the Town and Country Planning Act 1990. For a change of use, the period is 10 years. In both cases, a CLD for existing use (s191) can be obtained to formalise this.

If the work was recent and you're not sure it complies: get a CLD immediately. If the LPA decides it doesn't comply, enforcement action can include requiring demolition. Many issues can be regularised retroactively with a retrospective planning application.

Is a planning consultant needed for a straightforward householder application?

For a simple rear extension application: usually not, if you can draw basic plans. Many homeowners submit their own householder applications through the Planning Portal (the national online application system). For anything borderline (conservation area, large extension, unusual design), a planning consultant or architect adds value by improving the quality of the application and managing the LPA relationship.

Regulations & Standards