Planning and permitted development
What counts as the original house for permitted development?
Short answer
The original house is the house as it was first built or, if it was built before 1 July 1948, as it stood on that date. The definition is in article 2(1) of the General Permitted Development Order 2015.
Most permitted development limits for extensions, roof enlargements and garden buildings are measured from the original house. Anything added after 1948, or after the house was built, uses up the allowance, whoever built it and whether or not it had planning permission. A previous owner's kitchen extension or dormer can leave you with little or nothing to build without an application.
"original" means: (a) in relation to a building, other than a building which is Crown land, existing on 1st July 1948, as existing on that date; (b) in relation to a building, other than a building which is Crown land, built on or after 1st July 1948, as so built;
The Order uses a different word, "existing", for the house immediately before the new work. Height and eaves limits in Class A are measured against the existing house. Depth, width, volume and coverage limits are measured against the original.
Which limits use the original house
| Limit | Measured from | Paragraph |
|---|---|---|
| Buildings, other than the original house, covering no more than 50% of the curtilage | Curtilage less the original house's footprint | A.1(b), E.1(b) |
| Nothing forward of the front wall | Principal elevation of the original house | A.1(e), E.1(c) |
| Rear extension depth: 3 m, or 4 m if detached (up to 6 m or 8 m with prior approval) | Rear wall of the original house | A.1(f), A.1(g) |
| Two-storey rear extension no more than 3 m deep | Rear wall of the original house | A.1(h)(i) |
| Side extension no wider than half the house | Width of the original house | A.1(j)(iii) |
| New work joined to an earlier extension | The total enlargement must meet the limits | A.1(ja) |
| Loft enlargement: 40 cubic metres for a terrace house, 50 cubic metres otherwise | Cubic content of the original roof space | B.1(d) |
| Roof alterations no more than 0.15 m proud of the roof slope, and no higher than its highest part | The original roof | C.1(b), C.1(c) |
A worked example
A semi-detached house built in 1934. In 1985 an owner added a single-storey kitchen extension across the back, 2.5 m deep. You want to extend a further 3 m from the back of the kitchen.
- For a house that is not detached, paragraph A.1(f) allows a single-storey rear extension 3 m beyond the rear wall of the original house. The 1985 kitchen is not part of the original house.
- Your extension joins the kitchen, so paragraph A.1(ja) measures the total enlargement: 2.5 m plus 3 m, which is 5.5 m.
- 5.5 m breaks the 3 m limit. It is within the 6 m allowed by paragraph A.1(g) for a house that is not detached, but only through the prior approval process in paragraph A.4, which includes consulting the neighbours. The information you give the council has to describe the total enlargement (paragraph A.4(2)(a)(iv)).
- If the house is in a conservation area, A.1(g) does not apply and the extension needs a planning application.
The same arithmetic applies to lofts. On a terrace house where an earlier rear dormer added 30 cubic metres to the original roof space, only 10 of the 40 cubic metres allowed by paragraph B.1(d) are left.
How to establish the original house
The burden is on you. Government guidance on lawful development certificates says the applicant is responsible for providing enough information to support the application. The usual evidence is:
- The council's planning register. Earlier applications, decisions and certificates for the address show what was added and when. See how to read a planning history.
- Old Ordnance Survey maps. The National Library of Scotland publishes Ordnance Survey 25 inch maps of England and Wales from 1841 to 1952, and 1:1,250 and 1:2,500 National Grid maps from 1944 to 1975, free online. A footprint on a map from around 1948 is strong evidence of what stood then, though maps do not show heights or roof shapes.
- The building itself. Straight joints in brickwork, a change of brick or roof covering, and a change in floor level often mark where later work begins. A measured survey records it.
- Documents you hold. Building control completion certificates, old sales particulars, the builder's drawings and photographs.
Where two readings are possible, settle it before you design. An extension drawn to the wrong baseline can be refused at prior approval stage, or built and later found to need permission.
What this means for you
Before you rely on permitted development, draw the original house on a plan of the plot and measure every limit from it. The permitted development checker asks about earlier extensions for this reason.
If the history is uncertain, a lawful development certificate for the proposed work puts the question to the council before you build. It costs £274 for householder works from 1 April 2026.
Sources
- GPDO 2015, article 2(1) (definitions of "original" and "existing") legislation.gov.uk
- GPDO 2015, Schedule 2, Part 1 (Classes A, B, C and E) legislation.gov.uk
- Permitted development rights for householders: technical guidance, September 2019 gov.uk
- Planning practice guidance: lawful development certificates, paragraph 006 gov.uk
- National Library of Scotland: Ordnance Survey maps maps.nls.uk