A house extension can be a wonderful thing, transforming the property and showcasing the homeowner’s vision and eye for design.

While the list of regulations is thorough, not all house extensions require planning permission. Depending on your property, preferences, and personal taste, your ideal house extension could be very achievable.

The Value & Benefit of House Extensions

House extensions, by their nature, create additional usable space. This brings extra versatility to the layout of the house and, more often than not, an increase in the value of the property.

Beyond this, a house extension provides an opportunity to build a unique, personalised space, with aesthetics and finishes that speak to the individuality of the homeowner. Extensions can play to both the strengths of the property and the desires of the homeowner; be it a conservatory with year-round garden views, or a bespoke open-plan entertainment room to cater to - and impress - house guests. 

Where Planning Permission is Required

There are a number of instances where planning permission is required for extensions of any size.

Buildings such as flats or maisonettes fall outside of permitted development rights, meaning planning permission is a necessity for any extension. Houses built on conservation or designated land may also need planning permission for side or rear extensions.

Permitted development rights do not apply to certain specific extensions. Planning permission is needed for:

• Balconies or raised platforms
• Verandas
• Chimneys, flues or vent pipes
• Any proposed extension taller than the existing house
• Any proposed extension where the materials used do not match the existing house (with the exception of a conservatory)

Extension Rules & Limitations

Permitted development rights (also known as permitted development rules or allowances) vary depending on the property type. Take a look at the video guides available on the planning portal for some useful info graphics.

Single Storey Extensions

Extensions for detached houses may only cover half the area of land surrounding the house. This includes outbuildings such as a shed or garden cottage.

Rear extensions may not go further than four metres from the original house and may not exceed four metres in height. Side extensions may not front onto any road or highway, and can only extend a maximum of three metres from the original house.

Multi Storey Extensions

Multi storey extension rules tend to be more stringent than those applied to single storeys. Extensions cannot be taller than the existing height of the property, and as much as possible, the pitch of the roof needs to match that of the existing house roof.

Rear extensions may not extend further than three metres from the property and must be at least seven metres from the rear property line. Should any side extension ideas include upper-floor windows, these are required to be frosted (or otherwise obscure-glazed) and prevented from opening.

Terraced & Semi Detached House Extensions

Aside from the aforementioned extensions that require planning permission such as balconies or verandas, terrace and semi-detached houses allow for extensions of up to three metres without the need for planning permission. More expansive extensions may require a lawful development certificate (necessary if the property should go up for sale).

Because of the nuanced rules and technicalities, a permitted development extension on a terraced and semi-detached property benefits from the involvement of an architect designer and construction team. By partnering with Fabric, you secure both in one.

Detached House Extensions

Depending on the size of the house, homeowners can extend up to eight metres under permitted development rights.

However, as with semi-detached and terraced houses, it is recommended to consult an experienced architect to design the extension and navigate any technical factors

Take a look at the volume calculation diagrams completed on Lantern House to work out extension opportunities available: 

The project can also be found here

Complement Your House With an Exquisite Extension

Tap into professional advice, bespoke architectural design, and high-quality builds with Fabric. Based in Solihull, Birmingham, we are a collective of architects, designers and construction specialists passionate about creating beautiful spaces.

Peruse some of our previous projects, and contact us for any extension or design and build projects.