What makes a structure a building for planning

Whether a structure is a building for planning purposes decides which consent you need, so it is worth getting right before anything is delivered. Section 336(1) of the Town and Country Planning Act 1990 says a building includes any structure or erection and any part of a building, which is circular enough to be useless on its own. The working test the courts use looks at three things: size, permanence and the degree of physical attachment to the ground. A structure that scores highly on all three is a building, erecting it is operational development, and the question becomes whether a permitted development right covers it.

Why the question arises

Three situations bring it up.

A homeowner buys a pod, container or cabin and wants to know whether Part 1 of the GPDO applies at all, because permitted development rights for outbuildings are drafted around buildings, enclosures, pools and containers.

An enforcement officer has to decide which time limit runs. Operational development and changes of use have different immunity periods and different enforcement routes, so classifying the breach is the first step.

And a professional needs to know whether the floorspace counts: for Community Infrastructure Levy liability, for a floorspace threshold in a validation list, or for Building Regulations.

The answer is not the same in every regime. A thing can be a building for planning and a chattel for rating, or a caravan under the Caravan Sites and Control of Development Act 1960 and still be assessed as a change of use of land.

Size, permanence and degree of attachment

The three-fold test comes from the rating case of Cardiff Rating Authority v Guest Keen Baldwins and has been applied in planning for decades, including to a marquee re-erected each year for several months and to a large tower crane assembled on site. The three factors are weighed together rather than applied as hurdles.

Size matters because it goes to whether the thing reads as part of the land. A 10 m by 5 m timber lodge is a building whatever it stands on. A 1 m planter is not, however firmly it is bolted down.

Permanence is about intended duration and actual use, not about whether the structure could in theory be removed. Something present for most of the year, year after year, counts as permanent even if it is dismantled each winter. But a short-lived structure for an event, taken down after a fortnight, is normally not a building.

Attachment is the factor people over-weight. A structure resting on its own weight can still be a building. Services connected into it, a concrete slab beneath it, bolts, straps and ground screws all push the analysis towards a building, but the absence of attachment does not settle the matter.

Read together, the question is whether a reasonable person would say the structure has become part of the land. That is a judgement, which is why marginal cases end up at appeal.

Caravans, containers and pods

A caravan is defined by section 29(1) of the Caravan Sites and Control of Development Act 1960 as a structure designed or adapted for human habitation that is capable of being moved from one place to another, with twin-unit structures treated as caravans where they can be moved in two sections and fall within the statutory dimensions.

The planning consequence is different from the building analysis. Stationing a caravan on land is normally a use of that land rather than operational development, so the question is whether there has been a material change of use, and the familiar permitted development classes for buildings do not apply. Where a static unit is assembled on site, fixed to foundations and connected to services in a way that makes moving it impracticable, it stops being a caravan and becomes a building.

Shipping containers sit at the awkward end of this. A container dropped on a yard for a few weeks is a chattel. The same container sitting on a slab for three years, with a door cut into it and power run to it, is a building, and the fact that a lorry could in principle remove it does not help.

Garden pods and modular units are the same analysis with better marketing. Delivery on a lorry says nothing about permanence.

Structures that rest on their own weight

A few recurring examples, with the factors that usually decide them:

Part 4 of Schedule 2 to the GPDO is worth remembering here, because it permits buildings and plant needed temporarily for construction works on adjoining land, and the use of land for any purpose for a limited number of days a year. Several arguments about permanence disappear once Part 4 is applied properly.

Hot tubs, pergolas and garden rooms

A hot tub delivered as a self-contained unit and filled from a hose is a chattel in most cases, so no planning permission is needed for the tub itself. What catches people is the deck. A raised platform more than 300 mm above ground is excluded from Part 1 Class E, so a tub sunk into a raised deck takes the whole arrangement outside permitted development even though the tub alone would be fine.

A pergola is usually a structure rather than a building when it is open-sided and open-topped, but once it has a solid roof, side panels and a floor it is a building and the Class E limits apply, including the 2.5 m height cap within 2 m of a boundary.

Garden rooms are buildings. The live question for them is never whether they are buildings but whether the use is incidental to the enjoyment of the dwellinghouse, and the point at which more activity becomes a material change of use is argued far more often than the physical test.

Where the answer changes the consent you need

Classification feeds through to five practical consequences.

Which permitted development right applies, if any. The householder classes are drafted around buildings, enclosures, pools and containers, and a structure outside those words has no right to rely on.

Whether demolition is caught. Demolishing a building can need prior approval under Part 11 of Schedule 2 to the GPDO, and in a conservation area the removal of a building needs permission.

Whether listed building consent is engaged. A structure within the curtilage of a listed building that was there before 1 July 1948 can be treated as part of the listing, and on larger historic estates routine work is sometimes handled through a heritage partnership agreement rather than application by application.

Whether the floorspace counts for Community Infrastructure Levy and for validation thresholds, which turn on new build gross internal area.

And which enforcement route and time limit applies, since operational development and material changes of use are treated differently.

Getting certainty

Officers will give an informal view and it is worth having, but it binds nobody. For anything with real money attached, apply for a certificate of lawfulness of proposed use or development under section 192 of the Town and Country Planning Act 1990 before the structure arrives, or under section 191 if it is already there. A certificate is the only formal way to confirm that development is lawful, and it is the document a buyer's solicitor will accept.

The application needs to describe the structure precisely: overall dimensions including any base or deck, the method of support, whether services are connected, the intended duration of use and the intended purpose. Vagueness is fatal, because a certificate only covers what it describes. Where the case is arguable, a short Planning Statement setting out the three factors and why they point one way does more than a covering letter.

Illustrative example: a 4.8 m by 3.6 m insulated garden room on ground screws, 1.8 m from the rear boundary, 2.45 m to the flat roof, with power and water connected, standing on a 200 mm deck. It is plainly a building. The deck at 200 mm stays below the raised platform threshold, the height is under the 2.5 m boundary cap, and the structure is within Class E provided the use stays incidental. Raise the deck to 350 mm and none of that holds.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. To see the documents a structure of this kind usually needs, browse the report types on PlanScope.