PD Calculator

Many house extensions in England don't need a full planning application. Under permitted development (PD) rights, you can extend your home within certain size and design limits. Knowing whether your plans fit those limits can save months of waiting and hundreds of pounds in fees.

Our PD Calculator checks your extension against the main permitted development rules for houses in England. This guide explains those rules, what they mean in practice and when you'll still need permission.

What is permitted development?

Permitted development rights are a national grant of planning permission for certain types of work. If your project meets all the limits and conditions, you don't need to apply for planning permission. The rules for householders are set out in government legislation and explained in the government's technical guidance.

PD rights apply to houses. They don't apply to flats or maisonettes, and listed buildings need listed building consent for most changes.

How to use the calculator (PD Calculator)

1. Choose the type of house: detached, semi-detached or terraced.
2. Choose the extension: single-storey rear, two-storey rear or single-storey side.
3. Enter the depth beyond the original rear wall, or the width for a side extension.
4. Enter the height, and whether it's within 2m of a boundary and its eaves height.
5. Tell us about garden coverage, designated land and whether it's a flat or listed building.

The calculator shows whether your extension is likely to be permitted development, likely to need prior approval or likely to need planning permission, with a checklist of each limit.

The main rules for single-storey rear extensions

The larger home extension scheme allows deeper single-storey rear extensions, but you must notify the council and give neighbours a chance to comment through prior approval. It isn't available on designated land.

Two-storey rear extensions

A two-storey rear extension can be permitted development if:

• it extends no more than 3m beyond the original rear wall
• it's at least 7m from the rear boundary
• the roof pitch matches the existing house as far as practical
• it isn't on designated land

Side extensions

A single-storey side extension can be permitted development if it's no more than 4m high and no wider than half the width of the original house. Side extensions aren't permitted development on designated land.

Rules that apply to every extension

• Garden coverage: extensions and outbuildings together can't cover more than half the land around the original house.
• Materials: should be similar in appearance to the existing house.
• Front extensions: anything extending beyond the front wall facing a road isn't permitted development.
• The original house means the house as first built, or as it stood on 1 July 1948 if it's older. Previous extensions count towards the limits.

A worked example

You own a semi-detached house and want a single-storey rear extension 5m deep and 3.5m high, with eaves of 2.8m near the boundary. It's not in a conservation area.

• 5m is over the 3m standard limit for a semi, but within the 6m larger home extension limit.
• The height and eaves are within the limits.
• Result: likely allowed with prior approval.

At 3m deep, the same extension would be likely permitted development without prior approval. Try different sizes in the PD Calculator.

Designated land

Stricter rules apply in conservation areas, National Parks, Areas of Outstanding Natural Beauty (now called National Landscapes), the Broads and World Heritage Sites. On designated land, side extensions, two-storey rear extensions and cladding aren't permitted development, and the larger home extension scheme isn't available.

Article 4 directions

Councils can remove some permitted development rights in particular areas using an Article 4 direction. Some new-build estates also have PD rights removed by planning conditions. Always check with your council.

Permitted development isn't everything

Even if you don't need planning permission, you'll usually still need:

• Building Regulations approval, for structure, fire safety, insulation and drainage
• a Party Wall agreement if you're building on or near a shared wall or boundary
• permission from your freeholder or mortgage lender in some cases

Wales, Scotland and Northern Ireland

This calculator covers England. Wales, Scotland and Northern Ireland have their own permitted development rules, which are similar in places but differ in the details.

Checking your property's history

Before relying on permitted development, check whether the house has been extended before, as earlier extensions count towards the limits. Your council's planning records, often available online, will show previous applications. Also check your title deeds for restrictive covenants that may limit building work regardless of planning rules.