Do You Need Planning Permission for a Dormer

Adding a dormer window is one of the most popular ways to convert a loft and gain usable space in a home. It brings in natural light and increases headroom, often making the attic suitable for bedrooms, bathrooms or home offices. But whether or not you need planning permission to build a dormer depends on its size, placement and your property’s location. While many dormers can be built under permitted development rights, there are strict conditions you must meet to avoid breaching planning rules.

Permitted Development Rights for Dormers

In England, dormer windows are usually allowed under permitted development rights, which means they can be constructed without applying for planning permission. These rights only apply to houses, not flats or maisonettes, and may not apply if your home is in a conservation area, national park, or has had permitted development rights removed by the local authority through an Article 4 Direction.

For a dormer to qualify as permitted development, it must meet the following conditions. The dormer must be on the rear or side roof slope, not the front. It must not exceed the highest part of the existing roof. The additional volume created by the dormer must not exceed 40 cubic metres for terraced houses or 50 cubic metres for detached and semi detached houses. This volume includes all previous roof additions.

The dormer must be set back at least 20 centimetres from the original eaves, measured along the plane of the roof. It must not overhang the outer face of the wall and should use materials that are similar in appearance to the existing house. Side-facing windows must be obscure-glazed and non-opening below 1.7 metres from the internal floor level.

When Planning Permission Is Required

Planning permission will be required if the dormer is on the front of the property and faces the road, as this significantly alters the street scene. Permission is also needed if the dormer exceeds the size limits, projects beyond the roof ridge or uses cladding or finishes that differ from the rest of the property.

If your house is in a conservation area, Area of Outstanding Natural Beauty, or is a listed building, dormer windows may be subject to tighter controls. In these cases, you will need to submit a planning application and, for listed properties, obtain listed building consent. Councils may require the dormer to be set back further or use traditional detailing to match local character.

Dormers with balconies or Juliet windows often require permission, even if the dormer itself falls within volume limits. The addition of balustrades or French doors introduces issues of overlooking, design impact and structural complexity.

Building Regulations and Dormers

Even if your dormer qualifies under permitted development, Building Regulations approval is still required. This ensures the dormer meets structural safety, insulation, fire protection, headroom, ventilation and staircase requirements. If the dormer is part of a full loft conversion, the entire project must comply with Building Regulations.

You will need to appoint a builder or designer familiar with the rules for converting roof spaces. Building Control will check that steel beams are correctly installed, that the floor is reinforced, and that escape windows and fire doors are provided where necessary.

Neighbour Concerns and Overlooking

While planning permission may not be needed, neighbours can still raise concerns about dormers that impact privacy or block light. If the dormer includes side-facing windows or is particularly large, it is advisable to consult neighbours early in the process. Obscure glazing, restricted window openings and careful siting can help reduce the impact on surrounding homes.

In some areas, local design guidance may encourage the use of rooflights or conservation-style dormers rather than large box-style dormers. Councils often seek to limit visual disruption and preserve roof profiles, especially in streets with uniform architecture.

Examples in Practice

A homeowner in Leeds added a flat-roofed rear dormer to a semi detached house, increasing the roof volume by 40 cubic metres. As the dormer was set back from the eaves and used matching tile cladding, it qualified as permitted development. Building Regulations approval was granted, and the project was completed without planning permission.

In contrast, a property in Bath within a conservation area proposed a front-facing dormer on a Georgian terrace. Due to its position, size and design impact, full planning permission was required. The council requested a smaller, pitched-roof dormer with sash windows in timber frames to match the original features.

Certificate of Lawfulness

If you are unsure whether your dormer qualifies as permitted development or if you want formal confirmation for future resale or mortgage purposes, you can apply for a Certificate of Lawful Development from your local planning authority. This certificate proves that your project is legally compliant without needing full planning permission.

Conclusion

You do not always need planning permission to build a dormer. In many cases, especially for rear dormers on houses outside conservation areas, you can proceed under permitted development rights as long as the dormer meets strict size and design conditions. However, planning permission is required for front-facing dormers, dormers on listed buildings or in protected areas, or where the design exceeds the permitted development limits. Even if planning is not required, Building Regulations approval will always apply. Checking with your local authority and obtaining a Certificate of Lawfulness can provide peace of mind before you begin your project.