Planning Permission for a House Extension UK: The Complete Guide

Extending your home is one of the most effective ways to add living space and value without moving. But navigating the planning system stops many projects before they begin. This guide walks through exactly when you need planning permission, how to apply, what it costs, and what to do if your application is refused.

Permitted Development vs Full Planning Permission

Not every extension needs a planning application. Permitted Development (PD) rights allow certain works to proceed without formal consent — but the rules are specific and easy to misread.

As a general guide:

Extension Type	PD Usually Available?
Single-storey rear (within limits)	Yes — subject to height, depth and materials conditions
Two-storey rear	No — always requires full planning permission
Side extension	Often no — single-storey only, max half the width of original house
Front extension	Almost always no — must not front a highway
Wrap-around extension	No — treated as side + rear, usually needs PP

The critical PD limits for single-storey rear extensions under the Town and Country Planning (General Permitted Development) Order 2015 (GPDO):

Detached houses: up to 4m deep (or 8m under the Prior Approval neighbour consultation scheme)
Semi-detached and terraced: up to 3m (or 6m under Prior Approval)
Maximum eaves height 3m within 2m of any boundary
Overall ridge height no higher than the existing roof

For extensions beyond the standard 4m/3m limits (up to 8m/6m), you must apply for Prior Approval — a lighter-touch process where neighbours are consulted and the council has 42 days to decide. It is not the same as a full planning application, but it is not automatic either.

If your property is in a conservation area, AONB, or is a listed building, PD rights are either restricted or removed entirely for most external works. Check with your local planning authority (LPA) before assuming PD applies.

When You Need a Full Planning Application

You will need a householder planning application for:

Two-storey rear extensions
Side extensions that exceed half the original width or are two storeys
Any front extension visible from a highway
Extensions on listed buildings (which also need Listed Building Consent separately)
Properties in Article 4 Direction areas where PD rights have been removed
Any extension in a conservation area that would materially affect the character of the area

For a detailed breakdown of exactly what PD allows, including the Prior Approval neighbour consultation scheme, see our Permitted Development Rights UK extensions guide.

How to Apply: The Householder Application Process

All applications in England are submitted via the Planning Portal (planningportal.co.uk). Scotland uses ePlanning Scotland; Wales uses the Planning Portal for Wales.

What you'll need:

Location plan — Ordnance Survey-based, scale 1:1250 or 1:2500, showing the site boundary in red
Site plan — Scale 1:500, showing the proposed extension footprint, existing layout, and adjacent properties
Elevation drawings — All affected elevations at 1:100, showing existing and proposed
Floor plans — Existing and proposed at 1:50 or 1:100
Application form — Completed via the Planning Portal
Ownership certificate — Confirming you own the land, or that neighbours have been notified

Fees (as of 2026):

England: £206 for a householder application
Scotland: £230
Wales: £230
Northern Ireland: £195

Design and Access Statements

A Design and Access Statement (DAS) is only required for householder applications in designated areas — conservation areas, World Heritage Sites, or where the LPA specifically requests one. Outside these areas, it is optional but can be useful for demonstrating design quality. A well-written DAS explains how the extension respects the character of the area, relates to its surroundings, and addresses access needs.

Timescales: The 8-Week Decision Period

The council has 8 weeks to determine a householder application (13 weeks for major developments). The clock starts when the application is validated — not when it is submitted. Validation can take 1–2 weeks if documents are missing.

In practice, many LPAs take longer than 8 weeks. If they do, you can appeal on grounds of non-determination — but this is rarely the best outcome. Engaging proactively with the case officer during the 8-week window is usually more productive.

Pre-Application Advice

Most councils offer a pre-application advice service for a fee (typically £50–£250 depending on the authority). This allows you to discuss your proposal with a planning officer before submitting, getting informal feedback on likely issues. It is not binding but is well worth the cost on larger or more complex projects. It also demonstrates good faith during the formal application process.

Section 106 Agreements and CIL

Section 106 agreements (planning obligations) are legally binding agreements between the applicant and the council that may attach conditions to a planning approval — for example, a requirement to provide affordable housing contributions on larger schemes, or highway improvements. For a typical single-household extension, Section 106 is unlikely to apply.

The Community Infrastructure Levy (CIL) is a charge levied by some LPAs on new residential floor space. Many LPAs exempt householder extensions from CIL, but this is not universal. Check your LPA's charging schedule. If CIL applies and you do not submit a self-build exemption form before work starts, you may lose the exemption permanently.

How to Read a Decision Notice

A planning decision notice will either:

Grant permission — may include conditions (e.g., materials to match existing, no new windows on a particular elevation, work to begin within three years). Read conditions carefully — breaching them can invalidate the permission.
Refuse permission — with specific reasons cited. Each reason will reference a policy (local plan policy, NPPF paragraph, or both). Understanding which policy was cited tells you what needs to change in a resubmission.

Conservation Area Rules

In a conservation area, Permitted Development rights are significantly reduced. Works that would normally be PD require planning permission, including:

Cladding any part of the exterior in stone, artificial stone, pebble dash, render, timber, plastic, or tiles
Enlarging a dwelling by more than 50% of the original volume
Any alteration to a roof

The council will assess whether the proposed extension preserves or enhances the character and appearance of the conservation area. Materials, fenestration design, and roof form all carry significant weight. Use natural materials — brick, slate, timber — that complement the existing building.

Party Wall Obligations

If your extension will be built on or near a shared boundary, or will involve excavations within 3–6 metres of a neighbour's structure, you may need to serve a Party Wall Notice under the Party Wall etc. Act 1996. This is entirely separate from planning permission — you can have planning permission and still need to comply with the Party Wall Act. For a full walkthrough of when the Act applies and what it involves, see our Party Wall Agreement UK guide.

Building Regulations

Planning permission and Building Regulations are separate requirements. You can have planning permission but still need Building Regs approval, and vice versa. An extension will almost always require Building Regulations approval — covering structural adequacy, fire safety, thermal performance, and drainage. For a full walkthrough of the Building Regs process, see our Building Regulations Approval UK guide.

What Happens If Your Application Is Refused

Common refusal reasons:

Loss of daylight or sunlight to neighbouring properties
Overbearing impact on neighbours (often tested against the 45-degree rule)
Harm to the character of the conservation area or street scene
Insufficient separation distances between buildings
Failure to meet the council's design guide requirements

Your options after refusal:

Resubmit — Address the specific reasons for refusal in a revised scheme. A resubmission within 12 months of refusal is free in England.
Appeal — Submit an appeal to the Planning Inspectorate (England), DPEA (Scotland), or PEDW (Wales). Appeals are free and the window is 6 months from the date of the refusal notice. The vast majority of householder appeals are decided by written representations — no hearing required.
Do nothing — If the refused works fall within PD, proceed under PD and apply for a Lawful Development Certificate instead.

The appeal process is independent of the council. An Inspector reviews the decision afresh. Success rates for householder appeals run at approximately 30–35% nationally — lower if the refusal is well-reasoned and clearly policy-compliant. For a detailed guide to the planning appeal process, see our Planning Appeal UK guide.

Outbuildings and Garden Rooms

If you are also planning an outbuilding alongside your extension, note that outbuildings are governed by different PD rules (Class E rather than Class A/B). See our guide on Building an Outbuilding or Garden Room UK for the specific height, footprint and boundary rules that apply to detached structures.

Using Renovate Me to Plan Your Extension

Renovate Me helps you map out your full extension project before you spend a penny on fees. Upload your property photos, set your goals, and receive a step-by-step roadmap covering planning, structural requirements, and fit-out — with stage-by-stage guidance unlocking as your project progresses.