Class A to Part 20 – Additional two storeys on purpose built detached blocks of flats to provide dwelling houses; discussed with Associate Planner, Roy Hammond.
Carrying on from Boris Johnson’s ‘Build, Build, Build’ speech, our Associate Director, Roy Hammond discusses and shares the new Permitted Development Provisions, and in particular the part that relates to the construction of an additional two storeys of flats on existing detached purpose-built flat blocks.
Permitted Development Provision | Limitations & Conditions
It relates to the provision of dwelling houses only.
The existing building must be at least three storeys high above ground level, so you would not include a basement in that assessment.
It allows for the creation of a maximum of two storeys and that’s upon the topmost part of the principal building only.
The flats must be purpose-built from the very beginning, meaning if the flats are part of an office conversion, then the Permitted Development doesn’t apply in that scenario.
The Permitted Development, in terms of building operations allows for the strengthening of the existing structure, to take the weight of the additional two floors, but that doesn’t include any visible external support structures.
It allows for the relocation of an existing plant, or new plant on top of the roof for the additional two stories, which might include air conditioning equipment, fans, etc. but that plant can’t be any higher than the plant that existed on the roof of the existing building.
Building operations also includes, safe egress and ingress to the building including via new doorways, and fire escapes, and includes the creation of new ancillary facilities like storage, waste, cycle stores etc.
The buildings that it applies to, they must be constructed post 1st of July 1948, but before the 5th of March 2018.
Limitations excludes buildings that are in conservation areas, areas of outstanding natural beauty, national parks, SSSI’s all within 3km of an aerodrome, listed buildings, shadow agent monuments, all land within their curtilage.
Internally the new floors are limited to 3 metre internal heights, or the height of the former floors in the existing building, whichever is the lower of the two and they are measured internally.
The two additional floors can’t be any more than 7 metres above the highest part of the existing roof, excluding plants. In any event the additional two floors can’t take the existing building more than 30 meters in height, and again no visible support structures.

Planning Process | Permitted Development Provision
In terms of the planning process, that’s the Permitted Development Provision, that’s the bit that you can do as of right now.
But there is still a prior approval process to go through with the council, it is not supposed to be as onerous as going through a full planning application. The reality is that the matters that they can take into account don’t differ significantly from those that they would take into account as part of a planning application, and they include transport and highways impacts, contamination and flood risk, neighbour amenity, external appearance etc.
The submission itself requires, for example, a construction management plan, works specification, and floor plans. There is third-party consultation that would consult with the local town council, or community groups, or neighbours existing tenants, highway authority etc. so it would be subject to consultation.
It is important to note there’s no deemed approval, so if the council doesn’t determine within the defined time period, you don’t get permission as of right and also there is a three-year time limit on completion, so it’s not commencement, you’ve actually got to complete within three years of the grant of the prior approval.
If you have a building you think fits this bill, then, by all means, get in touch.