Rules for building Additional Storeys using Permitted Development
Transcription of the video
In this video, I go through the rules for building Additional Storeys using Permitted Development.
This is video No 7 in a series of videos that started with Video No 1 considering eligibility for Permitted Development.
It is recommended that you watch video 1 before you watch this one.
This video has 3 sections:
(1) Exclusions, looking at which houses are excluded from eligibility for Additional Storeys
(2) Limits, examining the detail of what can actually be built
(3) Conditions, looking mostly at how to engage with the planning authority
Exclusions
You cannot build additional storeys on a house if any of the following exclusions apply:
- A change of use has been granted;
- The house is on Article 2(3) land or on SSSI land;
- The house is Listed.
The house must be constructed between 01 July 1948 and 28 Oct 2018.
The onus of proof regarding the actual date of construction lies with yourself, not the council. And you need to prove that the entire structure was built in this period, not just part of the structure.
If the original house has been previously extended upwards (using Class AA or otherwise), the Additional Storeys benefit is not available.
Where a single-storey extension already exists, you can’t use the Additional Storeys provision to raise it upwards.
However, it might be possible to do this under PD rules if it is a rear extension. Check out video 3 on Rear Extensions.
The building must not contain a flat (Part 20 of the Permitted Development Order allows for new flats on properties that are not dwellinghouses).
Limits on the number of storeys
There are limits regarding the number of storeys that you can build: 1 additional storey
For a detached house, the roof ridge can be raised a maximum of 3.5m for an existing one-storey building, 7m for an existing multi-storey building.
For a semi-detached house, the roof ridge can be raised a maximum of 3.5m above the highest part of the neighbouring building. For an existing one-storey house, you can go up one storey.
If your neighbour has already raised their house, then you can go up one storey.
For an existing multi-storey semi-detached house, you can go up one storey. In this case from 2 to 3 storeys.
If your neighbour has already added another storey, you have a choice of adding one storey, or 2 storeys.
For a terraced house, the roof ridge can be raised a maximum of 3.5m above the highest part of the terrace. For an existing one-storey house, you can go up one storey.
If your neighbour has already raised their house, then you can go up one storey.
For an existing multi-storey terraced house, you can go up one storey. In this case from 2 to 3 storeys.
If your neighbour has already added another storey, you have a choice of adding one storey, or 2 storeys.
The overall height limit is 18m which, in practice, limits the building to just 4 storeys.
Assuming 3.5m per storey and 3m for a pitched roof, adding 2 storeys to an existing 2-storey house results in a total height of 17m.
The same height is achieved by adding 1 storey to an existing 3-storey house.
If the same house has a flat roof with a depth of half a metre, the overall maximum height achievable is 18m. This is achieved by adding 2 storeys to a 3-storey house … or by adding 1 storey to a 4-storey house.
Other Limits
The floor to ceiling height for an additional storey must be the lower of 3 metres, or the floor to ceiling height of any existing storey.
Any additional storey can only be built onto the principal part of the house. This means the main part of the house excluding any front, side or rear extension of a lower height, whether this forms part of the original house or is a subsequent addition.
Only the topmost storey of the house can be built on when constructing an additional storey.
Existing accommodation within the roof of a house is not considered to be a storey or a topmost storey.
The roof pitch of the additional storey must be identical to the existing roof pitch. You cannot build an additional storey with a pitched roof if there was previously a flat roof.
The development must not include a window in any wall or roof slope forming a side elevation of the house.
The materials in the development must be of a similar appearance to the rest of the house.
There must be no visible support structures on the exterior of the house upon completion of the development.
Any external works added to strengthen existing walls or foundations must not be outside the curtilage of the house.
Conditions
You will need to complete the development within 3 years and it must then be used as part of a C3 dwellinghouse or ancillary to the primary use as a dwellinghouse.
You will require Prior Approval from the local planning authority, who will consider its external appearance.
An appeal decision in 2021 has clarified the extent to which councils can make visual assessments. They only have the power to judge the appearance of the house as it looks itself – they cannot examine the development in context with the surrounding area.
The planning authority will also consider the impact on adjoining property and on any protected views
Thats it for this video
That was the last one of this series. If you have suggestions for other videos or even a completely new series, I’d love to hear from you.