Guide to Loft Conversions

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In this guide for homeowners thinking of undertaking a loft conversion, we provide an overview of what the process entails and answer some frequently asked questions, such as:

• Do I need planning permission for a loft conversion?
• Do I need building regulations approval for a loft conversion?
• Do I need a party wall agreement for a loft conversion?
• Do I need an architect for a loft conversion?
• How much does a loft conversion cost?

Most loft conversions do not require planning permission, but there are a number of criteria that determine whether permission is needed or whether it can be done under Permitted Development.

The first set of conditions are around the size and position of the dormer. Dormer extensions can’t be at the front, can’t be higher than the existing roof, and must be set back 200mm from the eaves. The volume being added (including any previous additions) must be <50m3, or <40m3 if terraced. Also, you can’t have a balcony (other than a Juliet balcony).

Then there are conditions around external materials, which must be similar to the existing ones found on your house. And, lastly, your house can’t be within a conservation area or AONB.

If any of these conditions are not met, you will need to apply for planning permission. If all conditions are met, you can proceed under Permitted Development, but it’s highly recommended to apply for a Lawful Development Certificate to confirm this and prove the legality of your loft.

Even if you don’t need planning permission, your loft conversion will almost certainly require Building Regulations approval. A loft conversion generally involves structural changes that will need calculations from a structural engineer. You will also need to demonstrate adequate fire safety measures and compliance with regulations for insulation, ventilation and drainage.

Your architect (with input from a structural engineer) will be able to provide all the required drawings, including the material build-up details of your walls and roofs.

Unless your property is detached, then you will likely need a party wall agreement with each neighbour your house joins to. This is because any structural work like steel beams will likely bear upon the party wall.

Although it’s possible to serve notices yourself, it’s normally recommended to use a party wall surveyor to make sure it’s done correctly. They can also arrange a photographic condition survey and negotiate an award if your neighbour objects. An objection from your neighbour won’t normally stop you converting your loft, it’s just a bit more time and expense.

Some loft conversion companies will offer a “full service”. However, we would always recommend using an architect to make sure you get the loft you want, to check everything is done correctly, and to protect your interests throughout the process. Loft companies may not use qualified architects.

An architect will design a loft bespoke to your requirements and provide all the necessary drawings both for planning and for Building Regulations. Your architect can also assist with the tender process to find the best builder for your project, arranging a number of quotations based on the same full pack of information.

Lastly, your architect can act as Contract Administrator during construction, conducting site inspections, approving invoices, and handling any requests from your builder for more time or money. We consider it more constructive and less risky to have a collaborative group of independent professionals, rather than handing full control to one company. 

There are a number of factors that will affect the cost of a loft conversion. The main ones are whether you want a dormer (or just roof-lights), the head height available, and whether your roof ends are hipped or gabled.

Head-height (after allowing for thicker floors and ceilings) should be at least 2.2m and ideally 2.4m. If your loft doesn’t have that, it might be possible to lower the ceilings of the floor below, but that obviously adds expense. If either side of your roof is hipped, that significantly reduces the effective floor space and a hip-to-gable conversion would likely be recommended, again with added cost.

Other factors include the intended use of your loft space as well as the level of finish. Most generally include a bathroom, which brings additional plumbing and drainage costs and also introduces more cost variability depending on the specification of your suite.

A loft conversion is an excellent way of adding extra space to your existing home, but you need to make sure you handle each phase correctly, including planning, Building Regulations, and Party Wall notices. As well as designing your bespoke loft, an architect can help guide you through all these, help you choose the right builder, and make sure the construction goes smoothly.

Your architect will normally be the only person other than you involved throughout the full project from start to finish and trying to save money on an architect may prove a false economy. Always use an ARB registered architect and an RIBA Chartered Practice. See our Guide to Using an Architect for more information.

Kingston Architects is an RIBA Chartered Practice with experience designing and delivering loft conversions, including in Kingston, New Malden, Barnes and Mortlake. Give us a call on 020 8240 2167 to discuss how we can help with your project.