Rules for building Side Extensions using Permitted Development
Transcription of the video
In this video, I go through the rules for building side extensions using Permitted Development
This is video No 4 in a series of videos that started with Video No 1 considering eligibility for Permitted Development. Video No 2 listed the 10 conditions applicable to all extensions.
It is recommended that you watch videos 1 and 2 before you watch this one.
The first thing to note is that only single-storey side extensions are allowed under PD (ie Permitted Development) rules. No double-storey side extensions are allowed
The overall height of a side extension cannot be more than 4m
The eaves of the side extension cannot be higher than the eaves of the original house
And, where the extension is within 2m of the boundary, the eaves cannot be higher than 3m
The maximum width of a side extension is half the width of the original house, measured at its widest point.
A side extension is not allowed on a side elevation that fronts a highway.
A wall forming a side elevation of a house is any wall that cannot be identified as being a front wall or a rear wall.
A terraced house may have zero or more side walls.
A semi-detached house will have 1 or more side walls.
The eaves of the side extension cannot be higher than the eaves of the original house
Previous Enlargements
Where a proposed extension is being joined to a previous enlargement, PD rules are applied to the dimensions of the total enlargement
For example, if a proposed side extension 3.6 metres high is added to an existing extension 4.1m high, the total enlargement is higher than the 4m limit and it cannot be built under PD rules.
In this example, adding a 3m-wide extension to an existing 3m-wide extension creates a total enlargement that is 6m wide. Both are less than 4m high but as the total enlargement is more than half the 10m width of the original house, it cannot be built under PD rules.
If an extension on a side wall extends beyond a rear wall without attachment to a rear wall, it is subject to the restrictions that apply to rear walls as well as the restrictions on side walls. These rear wall restrictions are detailed in video 3 of this video series, titled “Rear extensions”.
In this example, for PD rules to apply, the side extension must not go more than 3m past the rear wall of the semi-detached house.
Or 6m if prior approval for a larger depth has been obtained.
Where a single-storey extension partially or totally fills the area between a side wall and a rear wall, the restrictions for both side and rear extensions must be applied.
From the rear wall, the maximum depth varies according to type of house (terraced, semi-detached or detached) and whether prior approval for a longer extension is available.
From the side wall, the maximum width of the side extension is half the width of the original house
With prior approval secured for this semi-detached house, PD rules permit a maximum 6m depth for the extension from the rear wall. The maximum permitted width of the extension is half the 10m width of the original house. In this example, the 6m long by 4.5m wide extension is PD-compliant.
If the extension is moved back 2 metres, it extends 8m beyond the back wall and it does not therefore comply with PD rules.
Here the maximum width of the original house is at the rear and 50% of this dimension is the maximum allowable width of the side extension.
The side extension can run the full depth of the existing house, subject always to the 50% width condition.
Wraparound Extension
A wraparound extension is where the proposed extension projects beyond both the deepest rear wall and the widest side wall.
In this example, the entire enlargement is 10m wide and does not comply with the 50% of house width limit. It cannot be built under PD rules.
This is a similar example; it cannot be built under PD rules.
The development could occur in 2 separate stages. In the first stage, the side extension is built under PD rules.
In the second stage, the addition of the rear extension to the side extension could only be achieved by applying for planning permission.
This is because the width of the total enlargement under PD rules would be more that half the original house width.
However, both extensions could be added under PD rules by slightly adjusting the design. By ensuring that the rear extension is not connected to the side extension, the width of the side extension remains unchanged.
Here is an alternative design where the gap might be usefully designed as an enclosed patio.
Thats it for this video
In the next one, video No 5, I’ll go through the rules for building loft conversions using Permitted Development.
