Planning Permission for Loft Conversions and Extensions

Your Full Guide

The Most Asked About Part Of Projects

Of all the questions homeowners ask before starting a project, “will I need planning permission” comes up more than any other. The honest answer is that most loft conversions and many extensions don’t need it at all, thanks to permitted development rights. But, it depends on the specifics of your project and your property. This guide explains exactly what permitted development covers, when you’ll need to apply, and what the process looks like if you do.

Permitted development: the short version

Permitted development rights let you carry out certain building work without submitting a planning application. They exist so that reasonable, modest home improvements don’t get tied up in red tape. Most standard loft conversions and single-storey rear extensions fall into this category.

This doesn’t mean no rules apply. It means the rules are set in advance by national regulations rather than decided case by case by your local council. As long as your project stays within the limits, you’re free to proceed without formal planning permission. Step outside those limits, and you’ll need to apply.

Loft conversions: when permitted development applies

A loft conversion is usually permitted development if it meets all of the following:

It doesn’t exceed the volume allowance: 50 cubic metres for detached and semi-detached houses, 40 cubic metres for terraced houses
It doesn’t extend beyond the existing roof slope on the side of the house facing a road
It doesn’t exceed the highest point of the existing roof
It uses materials that match the appearance of the existing house
It has no raised platforms, balconies, or verandas
Side-facing windows are obscure glazed and at least 1.7 metres above the floor

If your home is in a conservation area, a national park, an area of outstanding natural beauty, or is a listed building, the rules are stricter and you’re more likely to need permission regardless of size.

How this varies by conversion type:

Velux or roof light conversions almost always fall under permitted development, as long as the roof lights don’t protrude more than 150mm from the roof slope
Hip-to-gable conversions are usually permitted development, provided the volume allowance isn’t exceeded
Dormer conversions are often permitted development, but the dormer must stay within the existing roof slope. If it extends towards the front of the house or includes a balcony, permission is likely needed
Mansard conversions almost always require planning permission, because they significantly change the shape and pitch of the roof itself

Extensions: when permitted development applies

Single-storey rear extensions are the most likely type of extension to qualify for permitted development, but the limits depend on whether your house is detached or attached, and how far you want to extend.

A rear extension is generally permitted development if it meets all of the following:

It doesn’t extend more than 6 metres beyond the rear wall for an attached house, or 8 metres for a detached house (under the extended permitted development scheme, otherwise 3m and 4m respectively)
It doesn’t exceed 4 metres in height
It’s built using materials similar in appearance to the existing house
It doesn’t take up more than half the garden
Side extensions are single-storey, no more than 4 metres high, and no wider than half the width of the original house

Two-storey extensions, side extensions beyond a single storey, and anything that significantly alters the front of the house are far more likely to need planning permission. As with lofts, conservation areas and listed buildings carry tighter restrictions.

Why might I still need permission, even if my project fits the rules?

A few things can override permitted development even when your project looks like it qualifies:

Article 4 directions. Some local authorities remove permitted development rights from specific streets or areas, often to protect the character of a conservation area. You won’t always know this applies until you check with the council
Lease restrictions. If your property is leasehold, your lease may impose its own restrictions regardless of planning law
Previous extensions. If your home has already been extended, this can reduce or remove your remaining permitted development allowance for further work

This is why a proper check with the local authority, or with us, is always worth doing before you commit to a design.

What if I do need planning permission?

It’s not something to worry about. The process is well established and the vast majority of reasonable applications are approved.

What happens:

Architectural drawings are prepared showing the proposed work
The application is submitted to your local planning authority, along with the required fee
The council reviews the application against local planning policy
A decision is issued, sometimes with conditions attached

Planning Permission Timelines and Costs

Standard applications typically take 8 weeks to be decided, though more complex projects can take up to 13 weeks. From 1 April 2026, a standard householder planning application in England costs £548 for work to a single dwelling.

Some loft conversions that extend upwards may instead qualify for the cheaper prior approval route, which costs £249. Fees are reviewed annually each April in line with inflation, so always check the current rate on the Planning Portal before applying. Permission, once granted, is valid for three years.

We can manage this entire process for clients who need it, including preparing drawings, submitting the application, and liaising with the council on your behalf.

My project doesn’t need permission. Am I done?

Not quite! Two things are worth doing even when permitted development applies.

Apply for a Lawful Development Certificate (LDC). This isn’t compulsory, but it’s strongly recommended, particularly if you’re near a conservation area boundary or think you might sell the property in future. An LDC is official confirmation from the council that your completed work was lawful. It protects you if planning rules change in future, and it answers any questions a buyer’s solicitor might raise when you come to sell.

Meet building regulations. Planning permission and building regulations are two separate things. Even if your project doesn’t need planning permission, it must still comply with building regulations covering structural safety, fire safety, insulation, and ventilation. A building control officer will need to inspect and sign off the completed work.

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Planning Permission FAQs

Do I need planning permission for a loft conversion?
Most loft conversions don’t, provided they meet the volume, height, and design conditions set out under permitted development. Dormer and mansard conversions are more likely to need permission than Velux or hip-to-gable conversions. We’ll confirm your specific situation at the survey stage.

What is the 4-year rule for a loft conversion?
This used to be the time limit for council enforcement against unauthorised work, but it changed in April 2024. The rule is now 10 years for all types of unauthorised development in England, not 4. If you have existing work that may be affected, we can advise on where you stand.

Do I need planning permission for an extension?
Many single-storey rear extensions don’t, as long as they stay within the size and height limits for permitted development. Two-storey extensions and significant side extensions are more likely to need permission.

What happens if I build without the planning permission I needed?
This is known as a planning breach. The council can issue an enforcement notice requiring you to undo the work, and in some cases apply for retrospective permission, which isn’t guaranteed to be granted. It’s always worth checking before you start rather than after.

How long does planning permission take?
Standard applications are typically decided within 8 weeks, though more complex cases can take up to 13 weeks. We recommend building this into your project timeline from the outset.

What is a Lawful Development Certificate?
A Lawful Development Certificate is official written confirmation from your local council that completed work was lawful under planning rules at the time. It’s not required, but it provides valuable protection and reassurance, particularly when selling your home in future.

Does planning permission cover building regulations too?
No, they’re separate. Planning permission concerns whether you’re allowed to build something. Building regulations concern whether what’s built is safe and structurally sound. Almost all loft conversions and extensions need to meet building regulations, regardless of planning permission status.