Loft conversion planning permission and building regulations
Most loft conversions can be carried out without planning permission under permitted development, but there are exceptions.
You will also need to follow building regulations regardless of the type of loft conversion you're considering.
In this guide, we share how to work out whether you need planning permission or not, the building regulations you need to consider, and any other permissions you may need in place before you start.
Be inspired to make home improvements. Sign up for our Home newsletter – it's free monthly
Do you need planning permission for a loft conversion?
Permitted development loft conversions
Permitted development (PD) allows homeowners to make alterations to their properties without having to go through planning, so long as the impact on neighbours or the surrounding environment is likely to be small.
You shouldn't need planning permission for a loft conversion if it satisfies the following conditions:
- The total area of the additional space won't exceed 40 cubic metres for terraced houses, or 50 cubic metres for detached or semi-detached houses.
- The extension does not rise significantly higher than the existing roof (the limits depend on the type of conversion and property).
- The extension does not significantly alter the appearance of the house.
- The property itself is not listed, protected or located in a designated area (like an area of outstanding natural beauty).
The level of impact that the conversion has on the existing property will determine whether or not you need planning permission for your loft conversion. Therefore, the type of conversion you opt for matters.
Here, we run through permissions for the various types. But if you're unsure, then you should always seek guidance from an architect or builder.
Do you need planning permission for a rooflight conversion?
Rooflight conversions are the most simple type of loft conversion. They typically only involve adding in skylight windows, a proper floor and a staircase.
You are unlikely to need planning permission for this type of conversion.
Do you need planning permission for a dormer conversion?
A dormer loft conversion is an extension that protrudes from the slope of the roof.
You typically won't need planning permission for this type of conversion, as long as the extension is relatively small.
If it extends past the edge of your roof, or above the top of your roof, you are more likely to need permission.
Do you need planning permission for a hip-to-gable conversion?
A hip-to-gable conversion involves straightening the sloped roof on one or both sides of the property. They don't increase floor space, just add additional headroom.
As a result, these conversions do not typically require planning permission.
Do you need planning permission for a mansard conversion?
Mansard conversions are by far the most disruptive type of loft conversion. They involve straightening the sloping of the roof on all four sides. This means the roof is almost flattened.
Because they require so much work, and significantly alter the visual appearance of the house, these conversions typically do require planning permission.
Find out how much a loft conversion costs in 2025
How to apply for planning permission
If you do need planning permission for your loft conversion, you can submit an online application.
The application you will need to use depends on where you live:
- England: Planning Portal
- Scotland: ePlanning Portal
- Wales: Planning Application Wales
- Northern Ireland: Planning Portal NI
Different countries require different information, so ensure you read their guides carefully before you submit your application.
You'll need to submit a Building Regulations application as well, and a site survey will be carried out, before your application is assessed.
How long does it take to get planning permission?
It should take no longer than eight weeks to get planning permission in most cases.
However, if your project is large or complex, it can take up to 16 weeks.
How much does planning permission cost?
Prices start from around £200, but the cost of getting planning permission depends on the type of permission and where you live.
However, if you live in a listed building, there is no fee.
You can check how much planning permission will cost using the planning portals listed above.
For further advice and a a step-by-step guide, see how to plan a loft conversion
Which loft conversion building regulations do I need to follow?
Regardless of whether or not you need planning permission, your loft conversion has to meet building regulations.
These are in place to make sure any work done is structurally sound, the new room is fire safe, and that sound is reasonably insulated between the loft and the rooms below.
The specific regulations that apply will depend on the type of conversion you have. We've outlined some of the key loft conversion building regulations here.
Loft conversion insulation regulations
You'll need to ensure that your loft has proper thermal and sound insulation.
Thermal insulation will help to keep your loft warm, and sound insulation stops movement in the loft from creating too much noise in the rest of the house.
Minimum height for loft conversions
The minimum height for loft conversions is 2.2 meters across at least 50% of the floor area.
If your loft doesn't meet this requirement, you can opt to lower the ceiling of the room below or modify your roof structure. These are both very labour intensive and expensive processes.
Loft conversion fire regulations
There are a number of regulations your loft will need to meet to ensure it's safe in the event of a fire, including:
- At least two escape routes (including escape windows)
- Fire resistant doors
- At least one smoke alarm
Loft conversion joist regulations
Joists are the horizontal structures that support the ceiling and floor of your loft. They are important in loft conversions to ensure the additional weight of the living space is supported.
During a loft conversion, joists must be assessed by a professional structural engineer to ensure they have the proper load-bearing capacity.
They might require additional reinforcements to meet regulations for structural integrity, fire safety, and sound insulation requirements.
Read more about the different types of loft insulation
Non-habitable loft conversion regulations
Non-habitable loft conversions make your loft usable as a storage space, but cannot be used as a living area.
They're a great option if you only need additional storage, have a limited budget, or haven't been able to get planning permission for a more extensive loft conversion.
The building regulations for non-habitable conversions are much less strict, but there are still some requirements, including:
- Proper ventilation and insulation
- Smoke alarms and fire escapes
There are also some regulations to ensure that the loft is not use as a living space, including:
- Using folding stairs or pull-down ladders instead of fixed staircases
- No permanent heating, electrical or plumbing systems
- Walls cannot be plastered
These conversions typically fall under permitted development rights, so you won't need planning permission.
Other agreements and regulations
Bat survey
If you think you have bats living in your loft, you'll need a bat survey, which can cost £300-£400.
Bats are a protected species and, if your loft is home to a roost of them, you may need to obtain a mitigation licence to carry out the work.
Party wall agreement
If the work you're planning is going to affect the wall that joins your house to your neighbour's, you'll need a party wall agreement. This is an agreement between you and your neighbour that ensures the work is fair and won't endanger your neighbour's property.
You'll need to give a Party Wall Notice – a summary of your proposed work and copies of your plans – to your adjoining neighbours. If they are concerned, they may request an independent party wall surveyor to approve the work.
The surveyor will inspect the plans and may request further documentation before signing off that the may work to go ahead, or asking for any reasonable amendments to be made.
Read more about party wall agreements and how to keep the peace with neighbours during building work