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Home & garden.

Updated: 30 Jun 2021

Loft conversion building regulations and planning permission

In this guide, you'll find out whether you need planning permission, and which building regulations you need to meet to start work on your loft conversion.
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Most loft conversions can be carried out without planning permission, but you'll still need to satisfy building regulations. Here, we give you the lowdown on planning a loft conversion.

It's important to know whether you'll need planning permission before you begin - especially as it can take a long time to get approval - and you'll also need to make sure that your conversion meets building regulations.

Below, we'll tell you how to work out whether you will need to get planning permission, what building regulations to consider, and any other permissions you may need in place before you get started.

Do I need planning permission?

To check whether you need to get planning permission, you'll need an architect or builder to confirm this. But as a guide, you shouldn't need planning permission if your proposed conversion 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 (this allowance includes not only any extra space you create with this loft, but also any previous additions that have been made, such as an extension)
  • The extension does not reach beyond the outermost part of the existing roof slope at the front of the house
  • The extension does not go higher than the highest part of the roof
  • Materials are similar in appearance to the existing house
  • There are no verandas, balconies or raised platforms
  • Side-facing windows are obscure-glazed (ie frosted or patterned to stop people seeing in)
  • Side-facing window openings are 1.7m or more above the floor
  • Your house is not on designated land, namely national parks, Areas of Outstanding National Beauty, the Broads, conservation areas and World Heritage sites
  • Roof extensions, other than hip-to-gable ones, are set back as far as practicable, at least 20cm from the original eaves
  • The roof enlargement does not overhang the outer face of the wall of the original house.

If you're unsure, or think you might need planning permission, an initial discussion with an architect or builder should be able to confirm this.

Planning permission is just one of the things you need to think about when getting your loft converted. We've heard from experts and homeowners about the top mistakes and frustrations, so visit our page on insider tips from homeowners and experts to make sure you avoid the same annoyances.

What building regulations will affect my conversion?

Regardless of whether or not you need planning permission, your loft conversion will have to meet building regulations approval.

Building regulations are in place to make sure that any work done is structurally sound, that 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. As a starting point, the elements covered by building regulation include:

  • Fire safety: fire-resistant doors will be needed to make the new room fire-safe. Mains-powered smoke alarms will also be needed.
  • Floor and beams: it's likely that new floor joists will be needed to support the weight of the new room.
  • Sound insulation: it's important to make sure that noise between rooms is sufficiently insulated.
  • Stairs: new stairs will be needed to provide escape in the event of a fire (retractable staircases and ladders aren't enough).
  • Walls: any new walls will need to support any existing or new roofs where existing supports have been removed.

This isn't the complete list - there are plenty more things to be taken into consideration when planning your conversion. You can find further information by visiting the government planning portal website, or by speaking with your builder, architect or local building control.

Will I need any other permissions?

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 to have a Party Wall Agreement. This is an agreement between you and your neighbour that aims to ensure that work done 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. You can find free templates for these online, or get help from your builder or architect. It's then up to your neighbour to sign their agreement. 

If they are concerned, they may request an independent party wall surveyor to approve the work. You can recommend a surveyor, but it's ultimately up to them to decide who they use, and you're obliged to pay for their services.

The surveyor will come and inspect the plans, and may request further documentation, before signing off the work to go ahead, or asking for any reasonable amendments to be made.

You can find out more about the Party Wall etc Act 1966 and what it covers by visiting the government planning website.

Protected Species

If you think you have bats living in your loft, you'll need to have a bat survey, which can cost £300 to £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.