How Big Can I Build my Home Extension

Extensions can be a fantastic opportunity to increase the value of your property whilst adding functional space to your home. Whether you opt to add additional space on the ground floor or to create extra rooms via a loft conversion, there are limitations to the amount of square footage homeowners can introduce. Restrictions around the size of your build depend on several factors and can often seem confusing, however our team of experts are on hand to answer all of your questions about home extensions and to help you navigate the rules around extending your home in 2024.

If you are extending your property or changing the external look of the building you will need to gain approval from your local council. This is via the route of obtaining either planning permission or applying under permitted development. To understand the difference between the two please head to our blog Planning VS Permitted Development. The route you take coupled with the available land to build will dictate how big you are able to build your extension.

Permitted development rights allow householders to improve and extend their homes without the need to gain planning permission providing the scope of the work falls within certain requirements. Currently a single storey extension can only cover half the area of land that surrounds the original house; however, a period of consultation was held earlier in the year to discuss relaxing the restrictions to provide homeowners greater flexibility to extend their homes and may result in changes to the current rules of permitted development.

At the moment, under permitted development for a terrace or semi-detached home, you have the rights to extend by up to 3m without the need for planning permission, this increases to 4m for detached properties. You are however prohibited from anything that builds out towards the main road and from single-storey extensions that exceed four metres in height. It is also important to note that permitted development rights do not cover wraparound extensions. Not every home can benefit from permitted development rights, those not able to include flats, maisonettes and listed buildings.

With an application for full planning permission your scope to build has greater flexibility; however, your plans do face the threat of rejection if they do not meet standards set by each local authority. These usually relate to the impact your extension may have on the obstruction of light or intrusion on the privacy of neighbouring homes. Working with an architect and planning expert at Home Tales, our clients have been able to successfully submit planning applications that have totally transformed properties. In SW18 we were able to create this incredible space which added an additional 32 SQM to the property, with a kitchen diner that includes a utility room, a pantry and a ground floor WC alongside multiple social and dining areas.  

Loft conversions are the most effective way to add bedrooms to your home by utilising otherwise unused space – however currently permitted development states loft extensions may not exceed the original roof space by more than 40 cubic metres in terrace houses, or 50 cubic metres in all other cases, and should be set back at least 20cm from the original eaves. Our team have worked to completely transform the functionality of homes with bedrooms, bathrooms and office space added to the properties. This mid-terrace family home located on the Southfield’s grid in Wandsworth benefitted from the addition of two double bedrooms and a bathroom, with 3 Velux windows installed to maximise natural light.

The same home showcases the importance that size isn’t everything, particularly when the space is well designed and beautifully finished. With a ground floor side infill extension only 11 SQM meter was added to the building but as the property had an existing outrigger, we could extend into the side alley to create one, large room. This has made room for a spacious kitchen and dining area with a large island and Crittall style doors that look onto the family garden.

If you have any questions about extensions, home renovation, planning or design our friendly team of experts is available to answer any queries you may have. You can call us on 0207 043 2378 or email us at

Want to know more about renovating your own home? You can book a free consultation with a design and planning expert to discuss your project and receive a free, no obligation quote – click to book now via our live diary.

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