Most single-storey rear extensions and loft conversions that stay within strict size limits fall under permitted development and need no planning application. Side extensions, two-storey extensions and any work to flats almost always require full planning permission. Conservation area status, listed status and Article 4 directions reduce or remove permitted development rights entirely.
It's the first question almost every homeowner asks, and the honest answer is: it depends on what you're building, what type of property you own, and where it sits. This guide explains how to work out which side of the line your project falls on before you spend money on drawings.
What is the difference between planning permission and building regulations?
Planning permission and building regulations are not the same thing. Planning permission is about whether you're allowed to change the property — its size, shape and appearance, and the effect that has on neighbours and the street. Building regulations are about whether what you build is structurally safe and properly constructed. Many projects need both, some need only one. Getting planning permission does not mean you can skip building control.
What does permitted development actually mean?
Permitted development rights let you carry out certain works without a full planning application. They exist so that modest, uncontroversial improvements don't clog up the planning system. The catch is that they come with detailed limits on size, height, position and materials — and exceeding any one of them takes you out of permitted development entirely.
Broadly, the kinds of project that often fall under permitted development include:
- Single-storey rear extensions within set depth and height limits
- Loft conversions that stay within volume limits and don't alter the roofline dramatically
- Modest outbuildings and garden rooms that cover only part of the garden
- Some porches, subject to size limits
Permitted Development quick guide: extensions
Single-storey rear extensions are limited to 4m on a detached house or 3m on a semi-detached or terraced house, extendable to 8m and 6m respectively under the Prior Approval (Larger Home Extension) scheme. Side extensions must be single-storey and no wider than half the original house. Front extensions are not permitted development and always require a full application.
| Extension type | Permitted development limit |
|---|---|
| Rear, single-storey — detached | Up to 4m (or 8m with Prior Approval) |
| Rear, single-storey — semi-detached or terraced | Up to 3m (or 6m with Prior Approval) |
| Rear, two-storey | Maximum depth 3m. Must be at least 7m from the rear boundary and strictly meet all dimensional, height and design requirements |
| Side | Single-storey only. Maximum width is half the width of the original house |
| Front | Not allowed under permitted development — requires full planning permission |
| Height limits (all types) | Maximum height 4m; eaves limited to 3m if within 2m of a boundary |
Permitted Development quick guide: loft conversion types and rules
Loft conversions are subject to volume limits of 40m³ on a terraced house and 50m³ on a detached or semi-detached house. Velux and most rear dormer conversions can fall within permitted development; mansards and L-shaped dormers usually require a full application. No loft conversion may exceed the highest part of the existing roof, and front-facing extensions are excluded.
| Type | What it involves | Permitted development position |
|---|---|---|
| Velux / rooflight | Adds skylights to the existing roof without changing its shape | Often fits under PD if volume limits are respected |
| Dormer (rear or side) | Box-shaped structural projection | Volume limits of up to 40m³ (terraced) or 50m³ (detached or semi-detached). Must sit back at least 20cm from the original eaves |
| Hip-to-gable | Converts a sloping hip roof end into a vertical wall | Common on detached and semi-detached homes |
| Mansard | Rebuilds roof slopes to a near-vertical angle | Usually requires full planning permission |
| L-shaped dormer | Two connected dormers, common on period terraced homes | Frequently exceeds volume limits, requiring planning permission |
General loft rules. A conversion cannot exceed the highest part of the existing roof. Front-facing extensions are not permitted under PD. Materials must match the existing property. Balconies and raised platforms are excluded.
When is planning permission always required?
Permitted development rights do not apply unless every requirement is strictly met. They are also removed on designated land, for listed buildings, for flats and maisonettes, where an Article 4 direction applies, and where extensions and outbuildings would cover more than 50% of the land around the original house.
| Exception | What it means |
|---|---|
| Designated land | Conservation Areas, National Parks and Areas of Outstanding Natural Beauty |
| Listed buildings | Always require full consent |
| Flats and maisonettes | Permitted development rights apply only to houses |
| Article 4 directions | Where the local council has specifically removed PD rights |
| Overdevelopment | Extensions and outbuildings cannot cover more than 50% of the land around the original house |
Do I need a Lawful Development Certificate?
Even when your project genuinely is permitted development, that's a claim you may later have to evidence — typically when you sell. A Lawful Development Certificate is the formal way to have a council confirm the works were lawful. Buyers' solicitors ask about this more often than people expect, and it is considerably easier to obtain before the work is done than years afterwards.
What drawings do I need for a planning application?
Either route needs accurate drawings. A planning application requires existing and proposed floor plans, elevations, and a site plan drawn to scale and to the standards your local authority expects. A permitted development or lawful development certificate application needs drawings that demonstrate the scheme sits inside the limits.
Our planning drawings start at £1,100 and are delivered within two weeks, with a 98% first-time approval rate across more than 150 projects. If your project also involves removing a load-bearing wall or adding a beam, the Full Package at £1,650 covers planning, structural calculations and building regulations together.
Does the answer change between local authorities?
The national permitted development framework is consistent across England, but its application is not. Individual authorities operate Article 4 directions, conservation area designations and local validation requirements that change both what is permitted and what a valid application must contain.
We prepare drawings to the submission standards of the authority receiving the application, including Surrey authorities such as Elmbridge, Guildford, Woking, Waverley and Mole Valley, and South London boroughs including Lambeth, Wandsworth, Merton, Croydon and Richmond upon Thames.
Please note: this guide is general information for UK homeowners, not a formal planning determination. Rules vary by local authority and by property — conservation areas, listed buildings and Article 4 directions all change what applies. We confirm exactly what your project needs as part of your free quote.