Curtilage disputes and the 50 per cent coverage test

The 50 per cent rule in permitted development is not about your garden. It is about your curtilage, and the two are different areas of land on a surprising number of properties. Classes A and E of Part 1 of Schedule 2 to the General Permitted Development Order 2015 both cap the ground covered by buildings within the curtilage, excluding the original house, at half the curtilage area. Get the curtilage 50 per cent test outbuilding calculation wrong and a shed that felt obviously permitted turns out to need an application.

What curtilage means in practice

Curtilage has no definition in the Order. The courts have treated it as a question of fact and degree, asking whether the land serves the dwelling as part and parcel of it.

The authorities usually cited are Sinclair-Lockhart's Trustees, where the test was framed around land serving the purposes of the house, and Dyer v Dorset County Council, which looked at the physical closeness and functional link between house and land. Later cases confirmed that a curtilage need not be small, which is why a large country house can have a correspondingly large one.

What follows from that is practical. Curtilage is defined by use and by physical enclosure rather than by the red line on your title plan. Land can be in your ownership, fenced in with the garden, maintained as lawn, and still sit outside the curtilage if its historic and current function is agricultural or if it was only recently enclosed.

Land that looks like garden but is not curtilage

Four situations account for most disputes.

A paddock enclosed from an adjoining field within the last few years, still grazed or cut for hay. A strip of former orchard taken into the garden when the boundary was moved. A plot bought from a neighbouring landowner and fenced but never physically integrated with the garden. And land across a lane or track from the house, where the physical separation breaks the part and parcel link.

In each case the council will say the curtilage stops at the older boundary, which makes the denominator in the 50 per cent calculation smaller and the percentage higher. That is the whole argument in most refused certificates.

The reverse happens too. Where a former outbuilding plot has been absorbed into the garden decades ago, with a continuous history of domestic use, it is likely to be within the curtilage even though the title shows two parcels.

How coverage is calculated and what counts

The arithmetic is simple once the boundary is agreed. Measure the ground area of the curtilage, subtract the footprint of the original dwellinghouse, and that is your denominator. Then total the ground area covered by everything else and compare.

Original dwellinghouse means the house as it was built, or as it stood on 1 July 1948 if it is older. Extensions added since then count towards the covered area rather than being excluded with the original footprint, which catches people who have already extended twice.

Class A, which deals with extensions, counts buildings. Class E, which deals with outbuildings and incidental structures, counts buildings, enclosures, pools and containers, so a pool or a large bin enclosure enters the sum even though neither is a building in ordinary speech.

Hard surfacing is the common misunderstanding. A gravel drive and a flagged terrace add nothing to the coverage figure, although they have their own rules on permeability and on front gardens.

Existing outbuildings, extensions and hard surfaces

Measure what is already there before designing anything new. On a modest plot with a rear extension, a detached garage and a workshop, the existing coverage can already be close to half the curtilage.

Two refinements worth knowing. Demolishing an existing outbuilding as part of the project frees up its footprint, and the calculation is made on the position as it will be after the works. And a building that straddles the curtilage boundary counts only for the part inside, which is an argument worth making where a barn sits on the line.

Where the sum is marginal, a measured survey is worth the fee. Scaling off a satellite image gives an answer accurate to a few per cent, and a few per cent is exactly the margin these cases turn on. Our note on garage conversions and the parking condition that follows covers a related trap, because converting a garage changes neither the coverage figure nor the parking obligation.

Paddocks, orchards and former agricultural land

Land in agricultural use is not in the curtilage of a dwelling, and putting a post and rail fence round it does not change that on its own.

Councils look at how long the land has been used domestically, whether it is physically enclosed with the garden rather than separately, whether it is maintained as garden, and what the planning history says. A paddock with a field gate to the lane, grazed by a pony, mown twice a year and separated from the lawn by its own hedge, will be treated as outside the curtilage however the deeds read.

Changing that position is a material change of use from agriculture to residential garden, which needs permission. Many householders have built on such land assuming the 50 per cent test gave them room, and the enforcement position is uncomfortable because the building is unlawful regardless of its size.

Evidence that supports a curtilage boundary

Build the evidence file before you need it, because retrospective evidence is always weaker.

1. Historic aerial photographs showing the boundary position at different dates.
2. Dated family photographs showing domestic use of the land.
3. Council tax, utility and maintenance records where they distinguish the areas.
4. Previous planning decisions and approved plans showing the site boundary.
5. A measured topographic survey with areas calculated and stated.
6. Statutory declarations from previous owners or neighbours describing use over time.

A Planning Statement that sets the evidence out in that order, with the areas tabulated and the calculation shown, gives an officer something to agree with. The same material supports a ground-mounted solar proposal, where the coverage question arises in the same way, as our note on ground mounted solar arrays in a domestic garden explains.

Getting the position confirmed before building

The only formal way to establish that works are lawful is a lawful development certificate. A certificate of proposed lawful use or development under section 192 of the Town and Country Planning Act 1990 asks the council to confirm, before you build, that what you propose is permitted development.

The fee is a fraction of a full application and the determination period is eight weeks. If the certificate is refused you have a right of appeal, and you have lost nothing except time. If it is granted you have a document that satisfies a conveyancer in ten years.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it.

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