Do I Need Planning for a Loft Conversion?

A loft conversion in London has the potential to add valuable space within the home. They are one of the most effective and cost-efficient forms of extension. Loft conversions in houses typically add bedrooms and bathrooms to a property. In a flat, the configuration is usually different, and a conversion can add bedrooms or in some cases, they can expand kitchen, dining and living areas.  

Home extensions in London do require some form of planning approval. There are two ways you can go about obtaining approval from your local council. We thought we would talk you through some of the options available to you when extending into your loft. 

Planning permission vs Permitted development 

There are two forms of approval that you can get from your local council. One option is via planning permission. Planning permission varies council to council, as each council has a different interpretation on the guidance. It’s very much open to interpretation by council and even by individual case officer. With planning permission, you are very much asking your local council for permission to undertake the development. Permitted development is different, as it’s not asking permission. You are notifying the council of your intention to build the development and proving that your proposal complies with permitted development guidelines. Once planning permission is approved, you are issued with an approval letter confirming your allowed to proceed with the build. With permitted development, you are issued with a certificate or a document which agrees your scheme complies with permitted development guidelines and you can proceed with the build. 

Both planning permission and permitted development are fairly similar in terms of the scope of work. Both require an application to be submitted to your local council, accompanied with drawings that show the existing and proposed illustrations. The main difference is the planning fee. Planning permission is approx. £200 and permitted development is approx. £120. 

Planning permission 

If you are in a flat or if your property resides within a conservation area, permitted development is not an option and planning permission is your only route to obtain approval from your local council. This requires an application to be submitted to your local council. The application is accompanied by a drawing set which shows the proposal in more detail. This must include a site and location plan, as well as existing and proposed drawings. The drawings generally included existing and proposed floorplans, relevant elevations (for a loft conversion its generally front elevation and rear elevation), and relevant sectional details. In most cases, a CIL form also needs to be completed as part of the application. If you are within a conservation area, it’s generally mandatory to submit a Design & Access Statement alongside the application. This is a detailed document that describes the architectural style of the area and highlights keys points about the proposal, such as the design and materials. We would also draw reference to any precedent within the local area to show the council that they have approved similar schemes. The Design & Access Statement supports your case for approval and increases the likelihood of receiving a successful application. In some cases, you might need additional documentation to be submitted alongside the application, such as a Flood Risk Assessment. 

If you want to raise the ridge height within your loft conversion, then planning permission is also your only option. The reason for this is because permitted development guidelines state that the roofline cannot be increased from the original line of the property. We frequently propose an increase to the ridge height. Most London properties have an internal floor to ceiling height of 2.1m in the loft (give or take 10/20cm). You need 2.1m for it to be comfortable, and for it to pass building regulations (to be classified as a usable bedroom). 

Permitted development

In a mid-terraced property, a loft conversion is allowed an allowance of 40 cubic meters. This is a pretty generous area, and on a typical 5m wide property, you can generally get two bedrooms and a small en-suite, or one large bedroom and a bathroom from this allowance. We frequently apply for our loft conversion proposals under permitted development, simply because they give the homeowner exactly what they need. If a homeowner does want to go larger, and their property allows them to extend further (past the 40 cubic meter allowance), then we might consider planning permission as an alternative. For permitted development, you need to submit a permitted development application form, along with existing and proposed drawings. For a loft conversion, you would need a drawing that gives evidence that the 40 cubic meter allowance has not been breached. We submit a volume drawing and calculation to show this on our applications.  

Planning permission & Permitted development 

Some local councils (such as Wandsworth) allow you do both planning permission and permitted development, which results in a very spacious loft conversion. In this case, we would apply for planning permission for the main dormer extension that sits over the main property. We would then use the homeowners permitted development rights to extend with a second dormer over the main outrigger. As you then have the 40 cubic meter allowance purely for the rear dormer, it means you can go the full length and width of the outrigger below, maximising space and basically mimicking the footprint of the first floor of the property.  

Read more about the types of loft conversions here.

If you want to discuss your project in more detail, get in touch with our team today on 0207 043 2378 or email us at You can also book a telephone consultation directly via our live bookings page here. We look forward to speaking with you more about your project. 

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