Measuring curtilage when a garden has been enlarged

If you bought the paddock behind your house and fenced it into the garden, you probably have not increased what you can build under permitted development. Curtilage measurement for permitted development is not the same as the area on your title plan, and for outbuildings the Order fixes the curtilage at a historic date rather than taking it as it stands today.

That single point catches out a lot of people who have paid for land expecting to unlock a larger garden building. The land is yours. The permitted development allowance did not move with it.

Curtilage is a planning concept, not a title plan

Curtilage has no statutory definition in the planning acts. It comes from case law, and the working description is land that serves the purpose of the house in some necessary or reasonably useful way, forming with it a single enclosure.

The courts look at three things: the physical layout of the land and the house, ownership past and present, and the use or function of the land past and present. All three, together. A field you own and use for grazing is not within the curtilage of your house just because you own it and it adjoins the garden.

Equally, land can be within the curtilage without being formally laid out as garden. A yard, a drive, a bin store area and a strip behind a garage are all typically curtilage.

So the first question is never what the deeds say. It is how the land is laid out, and what it is used for.

The date the Order fixes for outbuildings

Here is the provision that decides most of these cases. Schedule 2 Part 1 of the Town and Country Planning (General Permitted Development) (England) Order 2015 contains an interpretation paragraph which, for the purposes of Class E, defines curtilage by reference to a fixed date. For a dwellinghouse built before 1 July 1948 it is the curtilage as it existed on that date. For a house built on or after 1 July 1948 it is the curtilage as it existed when the house was built.

Read that paragraph in the current consolidated Order on legislation.gov.uk before you calculate anything, because the Order has been amended many times and the interpretation provisions have moved.

The effect is deliberate. Class E allows buildings incidental to the enjoyment of the dwellinghouse, subject to a limit on the proportion of the curtilage that buildings may cover. Without a fixed date, anyone could buy an adjoining field, call it garden, and multiply their allowance. The fixed date closes that route.

It also means two identical-looking houses on the same street can have different allowances, because one had a larger plot in 1948 than the other.

Land brought in from a field or paddock

Changing agricultural or paddock land into residential garden is itself development. It is a material change of use under section 55 of the Town and Country Planning Act 1990, and it needs planning permission.

People do it without permission all the time, usually by moving a fence and mowing. That does not make it lawful. It makes it a breach of planning control that may become immune from enforcement after the statutory period, at which point the use as garden is lawful even though it was never permitted.

Two consequences follow. The extended area may eventually be lawful residential garden, and still not count towards the Class E calculation because of the fixed date. And until it becomes immune, putting a building on it can attract enforcement action against both the building and the change of use.

Neither point is obvious from reading a permitted development guide, and neither is something a fencing contractor will mention.

What it does to the outbuilding allowance

Work the calculation in this order.

1. Establish when the house was built. Before or after 1 July 1948 decides which date applies.
2. Establish the extent of the curtilage at that date, from the evidence described below.
3. Measure the area of that historic curtilage, excluding the ground area of the original dwellinghouse.
4. Measure the ground area covered by all existing buildings, enclosures, pools and containers within it, other than the original house.
5. Compare the two against the proportion the Order allows, and check the height, position and other limits in Class E separately.

The buildings counted include ones you may not think of as buildings. A swimming pool, a large enclosure, an oil tank. Garages added since the house was built count. Extensions to the house count as part of the house rather than as outbuildings, but they reduce the remaining curtilage area, which is the point that catches people who have already extended twice.

Class A extensions work to different limits and a different set of tests, and the curtilage and principal elevation questions that arise under Class A sit alongside this, because the two classes do not use the word curtilage in the same way.

Evidence of when the land was incorporated

You are trying to show the extent of the curtilage at a date decades ago, which means documents.

Historic Ordnance Survey editions are the best starting point, because the 1:2,500 County Series and the post-war National Grid mapping both show garden boundaries, outbuildings and field divisions. Find the edition closest to the relevant date and note its survey and revision dates rather than only its publication year.

Then add aerial photography, which shows mown garden against grazed field in a way maps do not. Conveyances and older title plans help with ownership, though not with use. Statutory declarations from long-standing residents or former owners fill gaps, and they need to come from people with direct knowledge rather than from someone reciting what they were told.

Where the answer remains unclear, a lawful development certificate under section 192 of the 1990 Act is the only formal way to confirm that proposed works are lawful. It is determined on evidence and law rather than planning merits, and a grant is a document a purchaser or lender has to accept.

When a change of use application is the answer

Apply for planning permission for the change of use of the land to residential garden where you want the position regularised, where you need the land to count for anything, or where the land is in the Green Belt or a National Landscape, because in those places extending a domestic curtilage into open countryside raises policy issues on its own terms.

A short Planning Statement should cover the existing use of the land, how long it has been used as it is, the boundary treatment proposed, the visual effect on the wider landscape, and whether the extended area would be used for anything other than domestic garden. If a building is proposed at the same time, expect the council to assess both together, and expect the question of whether a garden office remains incidental to the house to come up.

Setting the calculation out so an officer can check it

Do not describe the calculation in words. Draw it.

Produce a plan at a stated scale showing the current curtilage in one line style and the historic curtilage in another, with the areas of each given in square metres. Hatch every existing building, enclosure, pool and container, and schedule them in a table with individual and total ground areas. Show the proposed building hatched differently, with its ground area, and give the resulting total as an area and as a percentage.

Attach the historic map extract you relied on, labelled with its survey and revision dates, and the aerial photograph if you used one.

An officer who can check your arithmetic in four minutes will do so. One who has to reconstruct it from prose will ask for more information, and that is eight weeks you did not need to spend.

This is general guidance, not legal advice. A lawful development certificate is the only formal way to confirm that works are lawful, and you should check the position with your local planning authority or a qualified professional before relying on anything here.

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