Planning Permission in 2026: What You Actually Need to Know

Planning permission is one of those topics that sends homeowners down a rabbit hole of gov.uk pages and contradictory forum posts. For an even deeper dive, see our comprehensive planning permission guide. Here's what you actually need to know in 2026.

In short: Most single-storey rear extensions up to 4m deep (detached) or 3m deep (semi/terraced) fall under permitted development and do not need planning permission. If you do need to apply, it costs £528 in England and typically takes 10-14 weeks.

Permitted development vs planning permission

These are two different things and people confuse them constantly.

Permitted development (PD) means you can build without applying for planning permission, as long as you stay within specific limits. It's not a free pass - there are rules about height, depth, materials, and distance from boundaries.

Planning permission is a formal application to your local council. You need it when your project exceeds PD limits or falls outside its scope.

Permitted development is not the same as "no rules." You still need building regulations approval, and you might still need a party wall agreement.

What you can do under permitted development

For a typical detached or semi-detached house:

Single-storey rear extensions

• Maximum depth: 4m (semi/terrace) or 8m (detached) under the larger home extension scheme
• Maximum eaves height: 3m
• Maximum overall height: 4m (within 2m of boundary: 3m)
• Materials: must be similar in appearance to the existing house

Loft conversions

• Volume limit: 40m³ (terrace/semi) or 50m³ (detached) - see our loft conversion cost guide for full pricing
• No higher than existing roof ridge
• Side-facing windows: obscure glazed, non-opening below 1.7m
• No verandas, balconies, or raised platforms

Other common PD works

• Internal alterations (always permitted, but building regs may apply)
• Replacing windows and doors (like-for-like)
• Solar panels (within certain limits)
• Garden buildings under 2.5m at the boundary

When you need full planning permission

You'll need to apply if:

1. Your extension exceeds PD size limits
2. Your property is in a conservation area, AONB, or national park
3. You live in a flat or maisonette (PD rights are very limited)
4. Your PD rights have been removed by an Article 4 direction
5. You're building a new dwelling (always needs planning)
6. You're making a material change of use (e.g. house to HMO)

The application process

Pre-application advice is optional but highly recommended. It costs relatively little and gives you an early steer on whether your proposal will be approved.

Building regulations - the other approval

Planning permission and building regulations are separate systems. You can have planning permission but still fail building regs (and vice versa).

Building regulations cover:

• Structural safety - foundations, walls, roof, steelwork
• Fire safety - escape routes, fire doors, smoke detectors
• Energy efficiency - insulation, glazing, heating
• Drainage - foul and surface water
• Electrical safety - new circuits and consumer unit changes
• Accessibility - Part M requirements

You can use either your council's building control team or an approved private inspector. Costs are typically £500–£1,000 for a standard extension. Our Certificates & Inspections guide lists every sign-off you'll need by project type.

Common mistakes

Not checking PD rights first

Some properties have had PD rights removed. Check your property's planning history on your council's website, or request a Certificate of Lawful Development (£121) for peace of mind.

If your builder tells you planning permission isn't needed, here's how to verify that.

Assuming your builder handles everything

Some builders include planning applications in their service. Many don't. Use our what to ask your builder checklist to make sure nothing falls through the cracks, and read our 5 things to check before hiring a builder for the full vetting process. Clarify upfront who's responsible for:

• Planning application (if needed)
• Building regulations application
• Structural engineer's calculations
• Party wall notices

Starting work too early

Building without the right approvals can result in enforcement action. In the worst case, you could be ordered to demolish the work. It's not worth the risk.

How MyBuildAlly helps

When you upload a builder's quote, our AI checks whether typical planning and building regulation costs are included or excluded. It's one of the most common scope gaps we flag - and one of the most expensive if you don't budget for it. See our guide to what a builder's quote should include for the full list of items to verify before signing. If you're planning a kitchen extension, planning costs are just one of many hidden expenses to budget for.

Upload your quote for a free check →