Planning Consultant - Chris Scott
Hi, I’m Chris,
I hold an MA in Planning and work as a Planning Consultant

The fact that your reading this post probably means you understand what a dormer is. However, its best not to presume, so below I will briefly discuss what a dormer is and the reasons why you may want to install a dormer. Then later in the post, we will discuss whether you will require planning permission to install a dormer on your property. First, for those of you in a rush, I’ll provide a quick answer to the question. However, I would encourage you to read the full article to fully understand the various scenarios.

Do you need Planning Permission for a Dormer?

If your dwelling retains its permitted development rights it’s likely you can install a dormer on either the side or rear elevations of your property. However, you cannot install a dormer on the principal elevation (facing the road) on your property without submitting a householder planning application.

What is a Dormer?

Large Flat Roof Dormer
Example of a large flat roofed dormer – Image: dezeen.com

A dormer is a structure which projects vertically from a pitched roof. Typically the dormer will contain a window. There are many different styles of dormer window. Some dormers replicate the style and pitch of the roof on which they are located. Others have flat roofs. Some dormers purely project from within the roof while others are referred to as a wall dormer. The common reason to introduce a dormer is to create additional head height and usable space. Often as part of a loft conversion. Dormers are also used to increase the amount of natural light into the room. However, roof lights such as Velux windows are also commonly used to increase the amount of natural light within rooms located in the roof space.

Dormers and Permitted Development (PD) Rights

So as mentioned in the ‘highlight’ answer to the question you can possibly install a dormer under permitted development rights (PD). A dormer comes under Class B of the General Permitted Development Order 2015 (GDPO). However, you should never presume your dwelling still holds its permitted development rights. For instance, previous planning permissions may have removed some or all of the properties PD rights. Therefore, if you do intend to install a dormer under the impression it complies with PD you may consider a Lawful Development Certificate to check.

Where can you Install a Dormer under PD Rights?

You can position a dormer on the side or rear roof elevations of your property. However, with PD there are various rules to the design of the dormer which you must adhere to, such as:

  • The top of the dormer cannot be higher than the ridgeline of the dwelling.
  • The volume of the dormer must be under 40m3 for a semi-detached property and under 50m3 for a detached property.
  • You cannot install a dormer as part of a raised balcony, verandah or any sort of raised platform.
  • The dormer must be set back 20cm for the roof eaves and must not project beyond the outside face of the wall.
  • The materials would need to be similar to the existing roofing materials of the property.
  • Side windows in the dormer would need to be obscurely glazed and non-opening.
  • If your property is located within Article 2(3) land which includes Conservation Areas, Areas of Outstanding National Beauty or a National Park you cannot install a dormer under PD rights.

The Volume of the Dormer and your Original Dwelling

As you will note from the bullet points above, PD rights set restrictions on the volume of the dormer. For semi-detached properties, the increase in volume must be under 40m3 and for a detached dwelling under 50m3. However, the actual wording from the 2015 GDPO states the following:

“(d)the cubic content of the resulting roof space would exceed the cubic content of the original roof space

Therefore the term original roof space is important, as it refers to the original dwelling. So, if your property has had previous extensions to the roof over the ‘original dwelling’ you will have to discount that increase in volume. Say for instance a previous owner received planning approval for a dormer on the principal elevation of the property. The volume of that dormer will have to be discounted from the maximum size of the side or rear dormer you can install under PD. So you would no longer be able to install an additional dormer up to the maximum of 40m3 and 50m3 respectively.

Householder Planning Permission for a Dormer on the Principle Elevation

So let’s presume you want to install a dormer on the principal elevation of your property. As previously discussed, you would need to submit a householder planning application to secure approval for the works. Before an application is submitted its important to review the street scene of the area and if any front facing dormers on neighbouring properties currently exist. In other words, will a dormer be seen a consistent with the local vernacular or an alien design feature?

The Design of the Dormer

When it comes to planning proposals they do not necessarily have to match the designs of neighbouring properties, but they must appear to sit comfortably within the character of the area. Therefore, if the prevailing design feature of other dormers on the neighbouring properties have a hipped roof, it’s likely the local planning officer will be looking for a similar design. This also ties into the use of materials. You should be specific on the planning application on the materials you intend to use. For instance, specifying a darker glazing frame to match the existing roof materials may help the dormer to appear less prominent. You may consider requesting pre-application advice from your local planning authority if you believe your planning application may be contentious.

Steel Flat Roofed Dormer
This dormer is faced in bare weathering-steel for a very modern design approach – Image: dezeen.com

Being vague with a planning application can create various problems. First, it could even lead to refusal as the planning officer may deem the applicant provided insufficient detail to approve the application. Another possible consequence is approval with a materials condition attached to the permission. This would then require a discharge of conditions application. Therefore additional time and effort for something that could have been addressed during the original planning application.

Reading Local Planning Authority Design Guidance before seeking Planning Permission

It’s often a good idea to try and find out if your local authority has published any local design guidance. Such documents are not equivalent to local planning policy, however, they may be given weigh in the ‘planning balance’ when it comes to making a decision. For instance, my own local planning authority in the Staffordshire Moorlands specify in their design guidance that they preference ‘cheeked’ dormers to suit local design characteristics. Cheeked dormers have vertical side wall projections opposed to the sides of the dormer being pitched to meet the roof surface.

Cheeked Dormer Windows
An example of cheeked dormer windows – Image: Homebuilding.co.uk

Conclusions on do you need Planning Permission for a Dormer

Dormers can be crucial design feature for some loft conversions to provide the required head height and useable space. However, poorly designed dormers and a poor choice of materials can negatively impact the property. Therefore it’s a good idea to review existing properties within the local area to asses different design ideas. As stated above, you do require planning permission for a dormer window on the principal elevation of your property. To secure approval it will require a design and scale which is sympathetic to your own property and neighbouring properties. If you require assistance to secure a lawful development certificate or planning approval for a dormer, please get in touch. 🙂