Do I need planning permission for my extension?

Major external transformation

If you are thinking about an extension to your home you may have heard that you do not need planning permission to build it. This could be the case, but make sure you do not fall foul to the various regulations for this.

Building work that does not need planning permission is said to fall under Permitted Development (PD) rights. This guidance can, on initial inspection, seem quite simple. However there are various aspects to it that add additional complexities.  Below is an overview of some of these.

Removed PD Rights

If your house is; within a local conservation area, within a National Park or is listed, Permitted Development rights do not apply. In addition many modern housing developments have had their PD rights removed too, you should be informed of this when you purchase the property.

Single Storey Rear Extensions:

Possibly the most common of house extensions that do not require planning approval, but it is not always clear cut.If you live in a terraced or semi-detached property you can extend out 3m from the original rear elevation. This is increased to 4m if your house is detached. However there are several other criteria to take into consideration too.

The height of the eaves must not be higher than 3m and the highest point of the roof must not be over 4m, or higher than an existing adjoining roof if this is lower. This is measured from the external ground level, adjacent to the extension, so if you are on a sloping site this could have an impact on whether it falls under PD or not.

Another key aspect of the rear extension is that it must not be built wider than the existing house. If it does, even by the smallest amount, this will require a planning application.

Recently the depth of the rear extension projection has been increased to 6m and 8m for terrace/semi-detached and detached houses respectfully. However this does not mean you can simple go and build this. You still need to submit the proposals to the council under the Larger home Extension: neighbour consultation scheme. This basically means that if your neighbours do not object to the larger extension you can build it. However, if they do it will need to go through the full planning application process and therefore could get refused.

The final key point to note with extensions within PD is that they must not exceed more than 50% of the total area of the land around the original house. This 50% should also include any previous extension, outhouses and sheds.

Two Storey Rear Extensions:

Possibly the most important guidance for a two storey extension is that if it is within 2m of a boundary it will need a planning application submitting. It also must not be within 7m of the opposite boundary.

The second key aspect of guidance is that a 2 storey extension cannot extend more than 3m from the original house, on both floors, no matter if the house is detached or not.

Many of the principals for single storey extensions and loft conversions also apply, such as matching materials, no balconies and obscured side windows.

Loft Conversions

Another common project that often falls within PD rights. There are however a few key stipulations to keep to.

You must not increase the volume of the house by more than 40 cubic metres for a terrace house, or by 50 cubic metres for a semi-detached or detached house.

Dormer windows are allowed on the side or rear elevations but not on the front or facing a road. Any side dormer must have obscured glazing and be non-opening, when they are within 1.7m of the adjacent internal floor level.

The materials must be similar to the existing house and it must not be higher than the original house roof.

Finally, no balconies or verandas are permitted.


Porches can be built on the front elevation of your house, as long as; the footprint does not exceed 3m², the highest point of it is a maximum 3m and no part of the porch is within 2m of the boundary that front the highway.


If you are unsure over your PD rights, some local authorities will provide confirmation of your proposals being within PD, this often requires a small fee and provision of plans and elevations. However, many do not offer this service and if you want confirmation you will be required to submit an application for lawful development.

It is also good to remember, if your proposed project is not within PD, it does not mean that it would get refused when submitted as a full planning application.

The notes above are just part of the full guidance for what are your Permitted Development rights. Full details can be found on the planning portal website. If you are in any doubt it is always recommended to talk to an architect or a planning expert.