The 50 per cent curtilage rule for garden outbuildings
Class E limits buildings, enclosures and containers in a garden to half the curtilage once the original house is deducted. Extensions count. Driveways do not. Here is how to do the sum.
The 50 per cent curtilage rule says that buildings, enclosures and containers in your garden, taken together and leaving out the original house, must not cover more than half the curtilage once the ground area of that original house is taken out of the total. It sits in Class E of Part 1 of Schedule 2 to the General Permitted Development Order 2015, and it is the limit that quietly rules out a garden room on plots that already have a garage and a shed. Extensions added to the house since 1948 count towards it. Patios and driveways do not.
What the coverage limit measures
Class E gives permitted development rights for buildings and enclosures within the curtilage of a house that are needed for a purpose incidental to enjoying the house. Garden rooms, sheds, greenhouses, garages, kennels and swimming pool enclosures all sit here.
The coverage condition compares two areas. On one side, the total ground area covered by buildings, enclosures and containers within the curtilage, other than the original dwellinghouse. On the other, the total area of the curtilage with the ground area of the original dwellinghouse deducted. The first must not exceed half the second.
Original dwellinghouse has a fixed meaning. It is the house as it stood on 1 July 1948, or as first built if it was built after that date. Everything added since then is a building in the curtilage that is not the original dwellinghouse, and it counts.
That last point catches people out more than any other part of Class E. A two storey side extension built in 1998 adds to the numerator and shrinks nothing from the denominator.
Working out the curtilage
Curtilage is the land around a house that is used with it and serves its purposes. It is not the same thing as your title boundary, and it is not the same as the red line on a planning application.
A paddock behind the garden, fenced separately and used for grazing, is not curtilage even if you own it and it appears on the same title. A lawn, a vegetable patch and a drive all normally are. Where a field has been absorbed into the garden at some point, the position depends on whether that change of use was lawful, and on how long ago it happened.
Measure the curtilage as it exists when you build, not as it was in 1948. But you cannot lawfully expand the curtilage to create headroom under the rule unless the land is already in residential use or the change of use has been authorised.
If the boundary of your garden has moved, or if part of the plot has always been used differently, get the extent agreed before you rely on a calculation built on it.
What counts towards the coverage
Anything that is a building, an enclosure or a container within the curtilage, apart from the original house. In practice:
- Extensions to the house built after 1948, whether under permitted development or with planning permission.
- Detached and attached garages, carports with a roof and sides, and car ports where they read as buildings.
- Sheds, garden rooms, home offices, summerhouses, greenhouses and log stores.
- Swimming pool enclosures, hot tub housings and pergola structures where they form an enclosure.
- Oil tanks, LPG tanks and storage containers.
- Kennels, stables and field shelters where they sit within the curtilage rather than on adjoining land.
Measure the ground area covered, which is the footprint, not the floor area and not the roof overhang. Where a structure has been demolished, it stops counting from the date it goes.
What does not count
Hard surfacing is the important exclusion. The condition is about buildings, enclosures and containers, so a patio, a driveway, a path or a hardstanding does not add to the coverage figure. Hard surfaces have their own separate rules under Class F, with conditions about permeability and surface water.
Walls and fences are dealt with under Part 2 rather than Class E, and are not part of this calculation. Nor is the original dwellinghouse itself, which is taken out of both sides of the sum.
An open swimming pool with no structure over it sits in an awkward middle ground, and different authorities take different views. If a pool is central to your plan, ask the council in writing before you design around an assumption.
Land in front of the principal elevation
Separate from the coverage limit, Class E does not permit any building, enclosure, pool or container forward of a wall forming the principal elevation of the original dwellinghouse. A front garden outbuilding needs planning permission regardless of how much space you have left.
On designated land, meaning National Parks, the Broads, National Landscapes, conservation areas and World Heritage Sites, two further restrictions bite. Buildings cannot go between a side elevation of the house and the boundary, and buildings more than 20 metres from any wall of the house are limited to 10 m² of ground area.
Permitted development rights can also be removed altogether by an Article 4 direction, which many councils have made over conservation areas. Check before you measure anything, and see how Article 4 directions work if one covers your street.
A worked illustrative calculation
Take a plot of 420 m² in total. The original 1930s semi covers 68 m² at ground level. Since then the owners have added a 22 m² rear extension and a 15 m² detached garage, and there is a 6 m² shed at the bottom of the garden. A 12 m² garden room is proposed.
| Item | Area |
|---|---|
| Total plot (curtilage) | 420 m² |
| Less original dwellinghouse footprint | 68 m² |
| Curtilage for the calculation | 352 m² |
| Half of that figure | 176 m² |
| Existing rear extension | 22 m² |
| Existing detached garage | 15 m² |
| Existing shed | 6 m² |
| Proposed garden room | 12 m² |
| Total coverage | 55 m² |
At 55 m² against a limit of 176 m², the proposal is comfortably inside the rule. The driveway and the patio play no part. Now change one fact: if the same plot were 150 m² rather than 420 m², the available coverage would fall to about 41 m² and the garden room would breach it. These figures are illustrative and the arithmetic on your own plot will differ.
Putting the figures on the plan
Even where you are relying on permitted development rather than applying for permission, write the calculation down. Draw a site plan at a stated scale showing the curtilage boundary, the original house footprint hatched separately, each existing building with its dimensions, and the proposed structure. Add a small table with the totals.
Then consider a lawful development certificate. An application under section 192 of the Town and Country Planning Act 1990 for proposed works is the only formal way to establish that what you intend is lawful. It costs a fee and takes eight weeks, and it is the document a buyer's solicitor will ask for in five years' time. A certificate refused because the sums are wrong still costs far less than an enforcement notice.
The supporting note for that application is where the measurements, the 1948 baseline and the assumptions about curtilage all get set out. PlanScope can draft that narrative alongside a Planning Statement if you do end up applying for permission, and will flag the site measurements it does not hold rather than inventing them.
To see which documents a householder project is likely to need, browse the report types.
This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it. A lawful development certificate is the only formal way to confirm that works are lawful. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.
Frequently asked questions
Do house extensions count towards the 50 per cent limit?
Yes. The condition excludes only the original dwellinghouse, meaning the house as it stood on 1 July 1948 or as first built if later. Any extension added since then is a building within the curtilage and its ground area counts towards the coverage figure, which is the point most householders miss.
Does a driveway or patio count towards the coverage?
No. The condition covers buildings, enclosures and containers, so hard surfacing is outside it. Driveways, patios and paths are dealt with separately under Class F of Part 1, which carries its own conditions about permeable surfacing and dealing with surface water within the curtilage.
How do I work out what my curtilage is?
The curtilage is the land around the house used with it and serving its purposes, measured as it exists when you build. It is not the same as your title boundary. A separately fenced paddock used for grazing is not curtilage even if you own it, while lawns, drives and vegetable gardens normally are.
Can I build an outbuilding in my front garden under Class E?
No. Class E does not permit any building, enclosure, pool or container on land forward of a wall forming the principal elevation of the original dwellinghouse. That restriction applies regardless of how much coverage you have left, so a front garden structure needs a planning application.
Should I apply for a lawful development certificate?
It is worth it if the sums are close or the curtilage is unclear. An application under section 192 of the Town and Country Planning Act 1990 for proposed works is the only formal way to establish that what you intend is lawful, and the certificate is what a buyer's solicitor will ask for later.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.