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How To Plan Your Loft Conversion

In many instances, an extension or addition to your house is considered to be permitted development, so you wouldn’t need planning permission for an extension. However, it’s important to know there are limitations to this, and set criteria that must be met. If you’re considering building an extension, it’s important to assess your options, decide on which type of conversion works best for you, and to find out whether any planning permission is required.

Here; we run through the most important considerations and factors of planning a loft conversation and why it’s so important to get it right.

Assess The Space

The first question you have to ask yourself is simple: is my loft space suitable for a conversion?

Although most basic conversions can go ahead without any planning permission, there are a few key exceptions to this, for example, if the loft space isn’t tall enough, you won’t be able to convert it. Ask a builder, architect, or surveyor to visit your home and assess the space for you. If you’re struggling to get someone in, try measuring the height of the space yourself, check what type of roofing you have, be it trusses or rafters, and keep an eye out for other conversions on your street. If your neighbour has a new extension, it’s a positive sign for your property.

Choose Your Conversion

There are a handful of options available for your loft conversion, each providing a unique solution, flexibility, and installation cost. Let’s take a closer look at the four main types of extension, their benefits, disadvantages and potential costs.

Velux Light

By far the cheapest and least disruptive option, Velux light conversions won’t make any changes to the shape or pitch of the roof. Instead, a skylight window is simply installed into the original roofing. Remember; you’ll need to have enough roof space without an extension for this type of conversion.


Suitable for almost any home with a sloping, or “pitched”, roof, dormer conversions are less expensive than hip-to-gable or mansard conversions, but will still add a good deal of extra headroom and floor space. Typically, a dormer loft conversion is when a box-shaped structure is added onto a pitched roof, expanding the headspace and overall size of the room. Dormers, in particular flat-roof dormers, are the most popular type of conversion.

Hip to Gable

Hip-to-gable conversions work by extending the sloping ‘hip’ roof at the side of your property outwards, to create a vertical ‘gable’ wall, creating more internal loft space. Mostly found on semi-detached properties with an existing hipped roof, the hip is extended up vertically to create a gable before a Rear Dormer is constructed at the rear of the property. This type of conversion will only work on detached or semi-detached houses, as it requires a free sloping side roof.


Suitable for most property types, including terraced, semi-detached, and detached houses, Mansard extensions run along the whole length of your house’s roof and will alter the angle of the roof slope. Much like a rear dormer, this will make the exterior wall almost vertical, extending the size of the property significantly. Often the most expensive type of conversion, a Mansard will result in a significant amount of extra space, height, and value to your home.

Analyse The Cost

The cost of your conversion will depend entirely on which form of conversion you decide upon. Velux solutions are the most cost-effective, as they require little planning and almost no building work. Whereas a Mansard conversion is almost always the most expensive option, requiring an entire roof transformation to be complete. Although Dormers and Hip-and-Gable conversions sit somewhere in the middle in terms of pricing, it must be stressed, every valuation fluctuates depending on the space, architect, and size of the job. Depending on your chosen conversion, the installation cost can range from anything as low as £5,000 for a simple Velux installation, up to and including somewhere in the region of £70,000 for a Mansard.

Adhere To Regulations

An essential requirement when planning a loft conversion, regardless of the need for planning permission, is to make sure your conversion meets building regulations approval.

These regulations are in place to ensure that all work performed is structurally sound, the space is fire safe, and there is reasonable insulation for sound and heat. There are major alterations to consider, such as the weight of the space, as it’s likely new floor joists will need to be fitted to support this. Don’t forget, a permanent staircase is a necessity, new smoke alarms must be fitted, and any new walls must be able to support any existing or new roofing where existing support has been removed in the conversion process.

Party Wall Agreements 

If the work you’re planning is going to affect the exterior wall that joins your house directly to your neighbour’s, you will need a ‘Party Wall Agreement’. This acts as a summary of the proposed work and provides an assurance that the work will be carried out safely, effectively and in the allotted time frame. You can find further information by visiting the government planning portal website, or by speaking with your builder, architect, or local building control.

Other considerations and checks to consider vary from property to property, so it’s important to be thorough. Remember, bats often live in lofts and are considered a protected species, if you were to plan an extension, you’d need a completed bat survey to ensure their safety before any structural work can begin.

Get Permission

Planning permission isn’t always required, as in most instances extensions to your property can be made without planning permission and are often considered permitted developments, however, there are some limits and set criteria to be aware of.

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 adheres to the following conditions:

●     The extension does not reach beyond the outermost point of the existing roof slope.

●     The size of the extension is no more than half the area of land around the “original house”.

●     The extension does not go higher than the highest part of the roof.

●     Materials are similar in appearance to the existing house.

●     The maximum height of your extension must be no higher than the existing house.

●     There are no verandas, balconies or raised platforms.

●     Your house is not on designated land, namely national parks, Areas of Outstanding National Beauty, conservation areas and World Heritage sites.

Please be aware these are just a handful of the stipulations to consider when planning an extension, if you’re unsure or think you might require planning permission, it’s worth setting up an initial discussion with an architect or builder to confirm this.

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