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

There are lots of websites which provide very basic answers to whether you need planning permission for a loft conversion. With this post, I wanted to provide information on more specific examples about when and if you can complete a loft conversion under permitted development and when a planning application is required.

If planning permission is required a householder planning application will need to be submitted for the loft conversion. This will require a location and block plan to be included which detail the precise location of your property. You will also need to submit scaled drawings which show the elevations and floor plans of the property.

Permitted Development (PD) Loft Conversions

For the moment, let’s presume your home benefits from permitted development rights (more on that below). With a loft conversion, you want to increase natural light and head height within the roof space. You can potentially do this under Class B and Class C PD rules.

PD Class B Roof Extensions

Under PD the amount of space you can add depends on if your property is a terraced or detached property. The following rules around volume increase and permitted development rights apply:

  • Terraced Properties – Volume Increase of up to 40m3
  • Semi and Detached Properties – Volume Increase of up to 50m3

Important Note on Class B Roof Extensions

The above information is where most websites who provide details on loft conversions leave it. However, the applicable volume increases for loft conversions under PD are based on the original dwelling, not the existing dwelling.

The point being, the roof space of the dwelling may have been previously extended with dormers. For instance, that increase in volume needs to be deducted from the volume of any additional roof extensions. Therefore, before you plan the additional space you wish to add for your loft conversion you need to understand your properties planning history.

Dormer Windows Loft Conversion
IMPORTANT: Dormers on the principle elevation as part of loft conversions do require planning permission and cannot be completed under PD.

Other PD Rules For Class B Roof Extensions

So we have covered the additional volume which can be added for a loft conversion under PR rules. However, as you probably suspected there are more rules which you must follow to comply with PD, which include:

  • Roof extensions to be no higher than the ridgeline of the existing property.
  • No roof extensions above the principle elevation of the property (typically the wall which faces the highway).
  • Dormer roof extensions to be set back at least 20cm from the eaves of the roof.
  • The roof extension must not extend beyond the outside face of the wall of the property.
  • No verandas, balconies or raised platforms.
  • Any side windows must be obscurely glazed and non-opening.

Materials must be of a ‘Similar Appearance’

Under permitted development the materials your roof extension use must be of a ‘similar appearance’. That means, in most instances, you should choose ‘like for like’. For instance, that means using the same roof tiles where possible, and similar glazing materials.

Now, the PD criteria for using materials of a ‘similar appearance’ is not a ‘hard and fast’ rule. If it was single-storey conservatory rear extensions wouldn’t be possible under PD, hence an exception was made. The government’s technical guidance on PD and roof extensions under Class B states:

“the materials used should be of similar visual appearance to those in the existing house, but does not mean that they need to be the same materials or match exactly. The visual impacts of the materials used will the most important consideration.” – DCLG

The requirement of roof materials similar to the existing property is to protect the visual amenity of the area. Furthermore, to reduce the loft conversions impact on local character.

Flat Roof Extensions

Let’s say for instance you wish to install a flat-roofed dormer as part of your loft conversion. If the property does not already have a flat-roofed dormer, you may be wondering what materials are acceptable? Well, government guidance states that flat-roofed extensions will not normally have a visual impact, so most conventional flat roofing systems would be applicable under PD. This could mean felt, lead, zinc, even rubber. Personally, after going through the process of looking at flat roof technologies I would advise on fibreglass. A properly installed fibreglass flat roof will last longer than the other methods and is easily maintained.

Hip to Gable Extensions

Besides adding a rear or side dormer under PD as part of your loft conversion there is also the option of a Hip to Gable extension. The video from Attic Designs shows the complete works involved going from a hipped roof to a side gable. In this example, they have also added a rear flat-roofed dormer as part of the loft conversion.

A hip to gable roof extension as part of a loft conversion.

With hip to gable roof extensions it very important that the additional volume is calculated correctly. There are several cases where an LDC has been refused and then dismissed on appeal as the volume of a pyramid has been calculated incorrectly. A good architect should not have a problem with this however and should be able to inform you if the hip to gable extension is beyond PD rules on volume. However, you need to remember the volume figures are based on the original dwelling and not the existing dwelling which may have had its roof previously extended.

Planning Portal Volume Calculator

The planning portal has a volume calculator which can be useful when you’re planning your loft extension on what you can potentially achieve under PD rules. It does have a separate volume calculator for dormers, but no specific volume calculator for the hip to gable roof extensions. There is a workaround though. You can first use the Gable End calculator to give you a volume figure for the completed hip to gable extension. Then use the ‘One Hip End’ calculator to get the volume of the existing property. Minus the ‘One Hip End’ volume results from the Gable End volume figure. The resulting figure is the volume of the hip to gable conversion.

No Roof Extensions under PD on Article 2(3) Land

Article 2(3) land includes National Parks, Areas of Outstanding Natural Beauty, World Heritage Sites and Conservation Areas. Therefore, before you proceed with a loft conversion under PD you need to be completely confident your property is not located within Article 2(3) land. You can conduct a planning search through your local planning authorities website. Most local authorities today have interactive planning maps which you can view to see if your property in within Article 2(3) land. It’s worth noting if you do live within one of these areas there may also be an Article 4 Direction placing a further restriction on permitted development. Please note, the Green Belt is not Article 2(3) land, and all domestic PD rights apply, even the larger home extension.

Checking your Loft Conversion complies with PD

Before you proceed with a loft conversion under permitted development in most cases I recommend a lawful development certificate (LDC) for proposed works is secured from your local authority. While determining the LDC the local planning officer will review the planning history of the property and any pervious roof extensions to the original dwelling. If they believe the proposed loft conversion complies with PD rules, they will issue a certificate. You will therefore not have to be concerned about a visit from an enforcement officer after completing your loft conversion.

In some instances, the local planning officer may have the perception that the loft conversion cannot be completed under PD, based on the planning history evidence available to them. It is in these circumstances where a planning consultant such as myself can review old plans and maps to potentially clarify the planning history of the property.

Class C – Roof Lights

A roof extension under Class B PD rights will provide you with additional space and head height for your loft conversion. However, under Class C you can also add roof lights (Velux being an example) to provide additional natural light. The only significant restriction with Class C and roof lights are that they must not protrude beyond the roof surface by more than 15cm or be higher than the ridgeline of the house. You can even add roof lights on properties located in Article 2(3) land.

Conclusion on Loft Conversions and Planning Permission

If your proposed works for your loft conversion do not come under the PD criteria above then you will need to submit a householder planning application to secure permission. It’s also important to note, not all properties have PD development rights intact. In some instances, the conditions attached to previous planning permissions remove PD rights. Therefore its very important to review the planning history and previous planning conditions a property is subject to. A lawful development certificate can, therefore, be useful to confirm the status of the properties PD rights.

If you require assistance with preparing and submitting a lawful development certificate or planning application for your loft conversion please get in touch. 🙂