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.

Find out how much a loft conversion costs

Do you need planning permission for a loft conversion?

You don't need planning permission if your conversion falls under permitted development. 

Permitted development (PD) allows homeowners to make alterations to their properties without getting permission. It applies to alterations that have a minimal impact on the surrounding environment. 

In order to be covered by PD, a loft conversion needs to fill a series of requirements. 

When you shouldn't need planning permission

You shouldn't need planning permission for a loft conversion if it satisfies the following permitted development conditions: 

• Volume: 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.
• Height: The extension does not rise significantly higher than the existing roof (the limits depend on the type of conversion and property).
• Materials: The extension does not significantly alter the appearance of the house. 
• Classification: The property itself is not listed, protected or located in a designated area (such as a conservation area or area of outstanding natural beauty). 

When you should need planning permission

You'll likely need planning permission if your conversion could cause a significant disturbance or alteration to the existing environment, for example, if: 

• It adds more than 40 or 50 cubic meters of space
• It extends beyond the plane of your existing property
• It significantly changes the appearance of your property (for example, a larger conversion, or a modern conversion on a traditional property)
• You live in a listed property, a conservation area or an area of outstanding natural beauty

What types of loft conversion need planning permission?

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're 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 end of the property (a double hip-to-gable is where you straighten both ends on a detached home). By opening up the additional headroom, they can significantly increase usable floor space.

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. 

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're unlikely to need planning permission for this type of conversion. 

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 

Loft conversion building regulations 

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 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.

Height

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 modify your roof structure by opting for a dormer conversion or mansard loft extension, or lower the ceiling of the room below. These are both labour-intensive and expensive processes.

Structural integrity

There are a number of regulations regarding the structure of your loft conversion, to ensure your home can support the extra load, and the conversion itself can support the weight inside. 

During a loft conversion, your structure must be assessed by a professional structural engineer to ensure it is safe. 

Fire safety

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

Staircase

Your loft conversion needs a staircase for access. If it's going to be used as a habitable living space, this staircase must be permanent (not foldaway). 

There are regulations around the angle, steps and handrails, among other things, and it must also have a landing at the top and bottom.

Ventilation and insulation

Given that loft conversions are particularly exposed, you need adequate ventilation to prevent condensation and mould. 

You'll also 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.

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 used 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. 

Can you use a non-habitable loft conversion as a home office?

According to a spokesperson from loft-conversion specialists Charles Grosvenor Ltd, a Which? Trusted Trader, the answer to this question is 'no' – a non-habitable loft conversion is essentially for storage use only: 

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're 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 on the work, 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

Loft conversion regulation FAQs

What's the 10-year rule for loft conversions?

If you carry out a loft conversion without the necessary planning permission, the council can normally force you to reverse it. 

However, the 10-year rule means that a council cannot require that you reverse a conversion if it was completed more than 10 years ago. 

It used to be a four-year rule, but it was extended in April 2024. 

Note that all loft conversions, regardless of when they were completed, must meet building regulations – these ensure the loft is safe to use. 

Can I put in stairs to my loft without planning permission?

Yes, you can. Your loft conversion will likely only need planning permission if it causes a significant disruption to the local environment, for example, if it's a very large conversion, or will make your house look notably different from the outside. 

As you can add a staircase to the interior of your property without disruption to others, you won't normally need planning permission. 

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