Planning permission is often required if you are looking to extend the overall footprint of your house; however, there are some exceptions. These such projects fall under the classification of Permitted Development (PD). PD is implied consent for the work that is to be carried out. If you are looking to add a little extra space without going for a massive extension or applying for planning permission, we’ve put together some information on PD and its legal requirements and restrictions.

N.B – If you live in a conservation area or a listed building, there may be higher limitations to what works you can do under PD. For all types of property development, it is worth checking with your local authority or a planning expert beforehand.

red brick house in street


You can add a single or double-storey extension providing you adhere to specific requirements; this type of extension is a good way to add space onto existing rooms. For example, a two-storey extension could add kitchen/dining room space downstairs while extending the master bedroom upstairs. For a single-storey extension, restrictions are as follows:
• The extension must not sit forward of the principal elevation.
• Materials used must be similar to that of the existing house.
• If it is in two meters of a boundary, the eaves must not be higher than three meters. If the extension is more than two meters from a boundary, it must be no more than four meters.
• For rear extensions, it must be no more than four meters in depth for a detached house and three meters for a semi-detached or terrace house.
• For side extensions, they must not be bigger than half the width of the original dwelling.
A two-storey extension must be built at the rear of the property. This also includes adding a second storey onto an already existing single storey.
• The extension must not exceed three meters in depth or be in seven meters of the boundary.

sketch of architectural plans

Loft Conversions

These types of conversions can be useful for adding a decent amount of floor space to the existing house. Under PD, you cannot raise the height of the roof so an existing decent sized loft will be needed. Generally, under PD, a space of up to 40m2 is allowed. To provide extra headspace, you can add dormer windows, providing they do not reach higher than the existing roof.


These types of buildings can include garages, garden sheds and summer houses. You can build an entirely new outbuilding providing it will not be used as self-contained living accommodation or have an antenna. Other criteria include:
• The building(s) must not cover an area of more than 50% of the total land of the house. This includes any existing outbuildings but does not include the area covered by the main house.
• Depending on the type of roof, there are height limitations. The highest allowed is a four-meter dual pitch roof. If the building is within two meters of the boundary, the height restriction is two and a half meters.
• Outbuildings must only be a single storey.
Existing outbuildings may also be eligible for conversion under PD. If the outbuilding is attached to the house, for example, a garage with a connecting door, you can convert it as long as you do not extend the footprint of the house. Please be aware that a standalone outbuilding will need permission of a different type.


Porches are usually small and do not require planning permission, however, you must remember that:
• The porch cannot be taller than three meters.
• If the boundary is adjacent to a highway, it must not be within two meters of the porch.
• The external ground area must be threem2 or less.

house with a porch and purple flowers

This guide is a useful start to planning any works to your home without having to apply for planning permission. If you would like to read more about types of planning permission, read our blog here. Martin Perry Associates offers structural design for a range house works including loft conversions and extensions. For more information on structural engineers in Exeter and the West Country, please don’t hesitate to get in touch.