Do You Need Planning Permission for a Dormer?

Thinking of adding a dormer to your loft? Dormer conversions are one of the most popular ways to extend upwards and add valuable space, but before you start building, it’s important to know whether you need planning permission.

In many cases, dormers fall under permitted development, meaning you don’t need formal permission. But there are exceptions, and getting it wrong could mean costly delays—or even having to undo the work.

Here’s everything you need to know about planning permission for dormer loft conversions in 2025.

A Dormer Loft Conversion: Explained

A dormer is a structural extension that projects vertically from a sloping roof, creating additional headroom and usable floor space in your loft. It usually includes one or more windows and is typically added to the rear of a house.

There are several types of dormers, including:

• Flat-roof dormer – the most common and space-efficient option

• Gable-fronted (doghouse) dormer – with a pitched roof

• Hip-roof dormer – sloped on three sides, often used on hipped roofs

• L-shaped dormer – ideal for certain Victorian or Edwardian terraces

Dormers are popular because they often avoid the need for a full planning application, but not always.

When Is Planning Permission Required for a Dormer?

You will need planning permission for a dormer loft conversion if:

• The dormer faces the front of the house (onto the street)

• Your property is in a conservation area, national park, or listed

• The dormer exceeds height limits (e.g., it’s higher than the existing roof)

• The materials used don’t match the existing property

• The extension includes a balcony or raised platform

• The dormer would significantly alter the roof’s appearance

If any of the above apply, you’ll need to submit a full planning application and wait for approval before starting work.

Permitted Development Rights for Dormer Loft Conversions

In most cases, a dormer loft conversion at the rear of the property is allowed under permitted development (PD) rules in England. This means you don’t need planning permission as long as you meet certain conditions:

• The total extension (including the dormer) must not exceed 40m² for terraced houses or 50m² for detached/semi-detached houses

• The dormer must not extend beyond the existing roof’s highest point

• It should be set back at least 20cm from the eaves

• No balconies, verandas or raised platforms are included

• Side-facing windows must be obscure-glazed and non-opening

• The materials used must be similar in appearance to the existing house

Always check with your local planning authority, as rules can vary slightly by council—and permitted development rights don’t apply to all properties.

How to Apply for Planning Permission for a Dormer

If your dormer conversion doesn’t meet permitted development rules, you’ll need to apply for planning permission. Here’s how:

1: Hire an architect or designer – They’ll draw up accurate plans for submission.

2: Prepare your application – You’ll need elevation drawings, a site plan, and a description of the proposed works.

3: Submit to your local planning authority – Most applications are handled online via the Planning Portal (planningportal.co.uk).

4: Wait for approval – Decisions usually take 8 weeks, but this can vary.

5: Get Building Regulations approval – Separate from planning, this ensures your dormer is structurally sound and meets fire and insulation standards.

Top tip: Even if you don’t need full planning permission, it’s worth applying for a Lawful Development Certificate (LDC) to prove your dormer was built legally under permitted development.

Common Planning Permission Mistakes to Avoid

Many homeowners fall into the trap of thinking “everyone else on the street has one, so I don’t need permission.” Unfortunately, it’s not always that simple.

Here are some common mistakes to steer clear of:

• Not checking conservation area status – This is a big one. Even minor changes often need permission in protected areas.

• Misjudging height and size limits – Going over the permitted volume can invalidate your project.

• Assuming your builder has it covered – It’s your responsibility to ensure permissions are in place, not your contractor’s.

• Skipping the Lawful Development Certificate – Without it, future buyers might question the legality of the build.

• Forgetting about neighbours – While you don’t always need their consent, keeping them informed can avoid objections during the application process.

You might not always need planning permission for a dormer, but it’s vital to check the rules before you start. If you’re unsure, speak to your local council or a planning consultant. A bit of preparation now could save you a lot of hassle (and money) later on.