Your guide - loft conversion building regulations

Are you thinking about carrying out a loft conversion to create more living space in your home? We love loft conversions and think they add so much to a home, whether it's a guest en-suite, playroom or study area.  

Remember that you must consider building regulations early in the planning process and ensure you get a completion certificate.

We answer the most important questions about loft conversion building regulations to help you on your renovation journey!


Do I need building regulations approval for my loft conversion?

You always need to ensure that your conversion is fully compliant with building regulations. This is to ensure your conversion meets health and safety requirements.

Many loft conversions don't require planning permission and can be carried out within permitted development. However, planning permission is separate to building regulations and, as carrying out a loft conversion will require a significant amount of structural work, you will need approval from building control.


What is the process for loft conversion building regulations?

We recommend that you apply for a Full Plan Submission as it's the most thorough and suitable for larger projects such as a loft conversion, however you can apply for a Building Notice. For a Full Plan Submission, the steps are as follows:


  1. You will require structural drawings for a full plan submission which a structural engineer can carry out. 
  2. You can apply either directly to a local authority inspector or an independent building control inspector.
  3. Many structural engineers or architects will do the application on your behalf for a small fee, however you can do this yourself too. 
  4. Your builder will then need to ensure that they notify building control at various stages of the work, to carry out checks. This will be at the outset, during and on completion. A good working relationship with a builder and inspector is important and the builder may call upon the inspector at other stages for advice.
  5. The site will be inspected at the end to confirm the loft conversion has passed building regulations. 
  6. Finally, you should get a completion certificate 8 weeks after completion - do make sure you get this and file it somewhere safe!!!


What is the cost of loft conversion building regulations?

Expect to pay around £500 for the structural drawings by a structural engineer. Remember that these drawings are important and are also required for your builder to work off of.

You will also have to budget for the inspectors fee which can vary depending on your location, the size and complexity of the project. We recommend that you budget from £300 - £900 for the building control inspector fees. 

You may also need to pay extra if you want your structural engineer or architect to apply for building regulations on your behalf.


What are the main things to consider for loft conversion building regulations?

The building control inspector will be focused mainly on the following (although there will be other areas they look at):

Existing & new structure


The existing timber floor of your loft (known as the joists) must be able to support the new living space. Where previously you may have had only a few items being stored in the loft, or nothing at all, the joists will need to be strengthened to support a new habitable living space which may include a bathroom and furniture.


The existing load bearing walls will be checked as to whether they run all the way down to the foundations. For example, if the walls are supporting new joists then there will need to be additional support added if the wall does not run to the foundations.


Any existing structural beams throughout the property should be checked too to ensure they can support the new weight under loft conversion building regulations. The foundations of the house should also be checked to ensure it can take the weight - generally this shouldn't be an issue when adding a loft conversion but will be a consideration.  


If your property has a truss roof (normally built after 1960s) then it's likely that it will have no load bearing structure so it's likely that you will need to add in supporting beams to convert your loft. Homes built before the 1960s have framed that can be opened easier and have the rafters strengthened and adding support.

Insulation and ventilation

The roof, dormers and walls will need to be appropriately insulated to prevent condensation and mould. Good quality insulation will help keep the space feeling warm in the winter and cool in the summer. Make sure you invest in the best quality insulation your budget will allow.

To remain in line with building regulations, as a minimum you need a U-value (a U-value measures how effective the material is as an insulator and the lower the better) of no more than 0.16W per metre squared. You will need at least 270 mm of mineral wool or 130 mm of PUR insulation to achieve this. This must be installed at the rafters if the room is inhabited. More insulation will reduce the U-value further, which will also reduce energy costs and reduce CO2 emissions.

The loft space will require ventilation and you will need extractor fans in the bathroom or en-suite, even if you have a window there, to allow proper ventilation and to reduce condensation.

Sound insulation will be required between any habitable rooms and, if your loft conversion is in a terraced or semi-detached property, you may need to provide sound insulation to the neighbouring loft.

Staircase requirements

A staircase must be provided in order to allow a safe access and exit to the loft conversion.

You should ensure that there will be room to build the staircase and that there is at least 2 metres of headroom over the stairs, to comply with building regulations. This can be relaxed to 1.8 metres at the edge of the stairway to allow for a sloping roof but you must have 2 metres at the centre.

All risers must be equal and there must be a fixed handrail along the staircase.

Fire safety and resistance

You must have appropriate means of escape in the event of a fire from your loft conversion. This includes fitting fire doors to protect the staircase or, if the loft conversion is open plan, an additional escape route will be required. The doors will also need to be fire resistant to ensure they meeting loft conversion building regulations.

Fire alarms must be mains wired and where the loft conversion is open plan, you may also be required to fit water sprinklers.



More details of the specific building regulations can be found on the governments planning portal.



What if I don't apply for loft conversion building regulations?

If you have bought a property where work has been carried out without building regulations approval, then you will need to apply for a building control regularisation. Most importantly this will ensure any changes are made to ensure the conversion meets health and safety requirements. Also, if you want to sell the property in the future, not having the building regulations completion certificate could cause the sale to fall through.



Is there anything else I need to consider?

In England and Wales, it is common that you may need to obtain a Party Wall Agreement when you are carrying out a loft conversion. This will normally apply if your property is a terraced or semi-detached property. To find out more about a Party Wall Agreement then read our expert advice.


Our article is a helpful guide but you must always consult your local authority when carrying out any structural changes to your property. 

Published: June 4, 2019

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