Rules on extensions to houses: How far can you extend your home?

Rules on extensions to houses: How far can you extend your home?

What are the rules on extensions to houses and are there limits to how far you can extend your home? Yes, there certainly are, but it really depends on the application that your proposal is submitted under. So I thought I would briefly explain the limits under each application relevant to existing homes and the value in having a clear planning strategy that is right for your project.

We recently received planning permission for a side return extension and a loft conversion in Greenwich. Nothing really extraordinary about this as we regularly gain planning permission for this type of project across London.

What was different however, was our planning strategy.

I had learnt from a previous project that the local authority was unlikely to approve the proposal if submitted under the Householder Planning Application even though the property is not in a Conservation Area. The furthest the side extension could go under the council’s Supplementary Planning Document (SPD) was 3.6 metres even though extending 6 metres was clearly feasible without affecting daylight to the neighbouring property. So instead, we submitted two different applications, one for the side extension and the other for the loft. Certificate of Lawful Development for the loft and Notification for Prior Approval for the side extension.

Why apply for Certificate of Lawful Development for the loft instead of submitting under Householder Planning Application?

The council’s SPD provides further details on the local planning policy, which sets out the council’s vision for development in the area. The SPD is the guide to read to understand what is likely to be approved under Householder Planning Application in your area. I understood from the document that a proposal for a large dormer would be refused if submitted under Householder Planning Application. But a large dormer was exactly what my clients needed in order to maximise useable space in their loft.

A large flat roof dormer to the rear would be seen by the council as overbearing, with two small dormer windows with pitched roofs preferred instead.

However, if we applied for a Certificate of Lawful Development for a large flat roof dormer, the proposal would be within the permitted development rights and its rules on extensions to houses. Permitted development rights cover types of work that can be carried out without requiring planning permission.

As a terraced house, we could create 40 cubic meters additional roof space. The dormer couldn’t go higher than the highest point of the original roof, it couldn’t project beyond the external wall below, and it needed to be built in similar materials to the original house.

Although, work that falls within the limits of permitted development can be carried out without needing planning permission, it is advisable to apply for Certificate of Lawful Development as proof when selling the property that what has been built falls within the permitted development limits and rules on extensions to houses.

Why submit the side return extension under Notification for Prior Approval instead of Householder Planning Application?

Under the council’s SPD, the side extension could not extend beyond 3.6 metres, even though extending beyond this limit would not affect the daylight to or the outlook from the neighbouring property.

As with the loft, the side extension dimensions fell within permitted development rights, but under new rules on extensions to houses introduced in 2015. These rules increased the extent of permitted development rights limits for a single storey extension from 3 metres to 6 metres for attached houses and from 4 meters to 8 metres for detached houses, and whilst not covering more than 50% of the original garden space. However, building under these rules are subject to consultations with neighbours that share the boundary, and so seeking approval before carrying out the work is necessary. If the council receives objections from neighbours, the council could refuse approval.

For our side extension in Greenwich, which extended approximately 6 meters from the rear wall, we were successful in getting approval.

So if Permitted Development Rights generally allow increased development, when should one submit under Householder Planning Application?

Whilst greater volumes and dimensions can be obtained under permitted development rights, there are restrictions – one being that new external facing materials must match those of the original house. So if the main roof has clay roof tiles, then the same material must be used for the dormer. Not very modern if you’re looking for a contemporary aesthetic. You would need to submit under Householder Planning Application if your proposal includes new materials that differ to those of the original building.

And it’s also worth remembering that local planning policies differ from borough to borough, so whilst I refer to Greenwich Council’s SPD in this post, the SPD that applies to your borough will be different, and you may very well be allowed to extend more than 3.6 metres under Householder Planning Application.

So, what are the rules on extensions to houses and how far can you extend your home?

The rules on extensions to houses and how far you can extend your home really depends on what you’re looking to achieve in terms of scale, materials, design and as a result, the application that on balance meets your objectives. Permitted development rights might afford more volume, but limit the overall aesthetic. On the flip side, Householder Planning Application might result in a development that is visually interesting.

Whichever planning application you decide to submit under, remember that having a planning strategy that best suits your own specific project requirements and constraints is key to getting planning approval.

I hope I have shed some light on rules on extension to houses and how far you can extend your home. If you have more questions that you would like to ask, leave me a comment below or let’s tweet chat on Twitter.



  1. Tabitha says:

    Very informative article, with some great insights on the different types of planning applications and how they can affect the visual outcome of your extension. It’s also necessary to factor in the differing times these planning permission applications take so you can budget accordingly and plan your work around these different timetables.

Leave a Reply

Your email address will not be published. Required fields are marked *