Conservatory vs orangery vs extension: what's the difference and do you need planning permission?

"Conservatory," "orangery" and "extension" are often used loosely, but they describe genuinely different types of structure, with different costs, different levels of thermal performance, and different treatment under planning and building rules. Getting the terminology right matters before you start speaking to installers or architects, because the classification of your project can directly affect whether you need planning permission, whether building regulations apply in full, and how the finished space can legally be used.

A conservatory is generally the most heavily glazed of the three, typically built with predominantly glass walls and a glass roof designed to maximise light and a connection to the garden. Industry convention, rather than a strict legal definition, commonly draws the line at roughly 75% roof glazing: above that threshold a structure is usually described as a conservatory, and it's this high proportion of glass that also underpins its potential exemption from building regulations, discussed below.

An orangery sits between a conservatory and a full extension. It typically uses more brick or rendered masonry, often in the form of pillars or a low wall, combined with a solid or part-solid roof, frequently topped with a central glazed lantern rather than a fully glazed roof. Because more of the structure is masonry and thermally solid, an orangery tends to feel more like a permanent room of the house, and because its roof glazing usually falls below that same rough 75% threshold, it is commonly treated as a standard extension for building regulations purposes rather than benefiting from the conservatory exemption.

A traditional extension is the most integrated of the three: solid walls, a solid insulated roof, and full compliance with building regulations for structure, insulation, drainage and ventilation, in the same way as the rest of the house. This generally gives an extension the greatest flexibility of use, since it can be treated as ordinary habitable space all year round rather than a room with more limited heating or insulation. Sources broadly agree that extensions tend to cost more than conservatories, reflecting the more substantial construction and full regulatory compliance involved, but any precise costs you're quoted will depend heavily on size, specification and location, so it's worth treating figures as project-specific rather than assuming a fixed multiple.

In England specifically, many single-storey rear conservatories and extensions can be built under permitted development rights without a full planning application, though the limits matter. Common thresholds include not extending beyond the rear wall of the original house by more than roughly three metres for an attached house or four metres for a detached one (extendable to around six or eight metres respectively via a prior approval process, where the property isn't on designated land or within a site of special scientific interest), a maximum height of around four metres, reduced eaves height near boundaries, and a rule that extensions and other additions shouldn't cover more than about half the garden area around the original house. These permitted development rights don't apply uniformly everywhere, though — listed buildings, flats, and properties in conservation areas or on other designated land are commonly subject to tighter rules or may have no permitted development rights at all, so it's always worth checking with your local planning authority before assuming a project is exempt.

Building regulations exemption is a separate question from planning permission, and it applies specifically to conservatories. In England, a conservatory is typically exempt from building regulations where it's built at ground level, has an internal floor area of less than roughly 30 square metres, and is separated from the main house by an external-quality wall, door or window rather than opening directly into it, with any heating in the conservatory run on independent controls separate from the house's main system. Since April 2023, the thermal separation requirements underpinning this exemption have been tightened, generally requiring the separating wall, roof and floor to be insulated to an external-element standard and a thermally efficient door fitted between the conservatory and the house. If those separating doors are later removed, or the space is knocked through and heated as ordinary living space, the exemption is typically lost and the relevant building regulations then apply retrospectively.

It's important to be clear that all of the planning permission and building regulations detail above relates specifically to England. Scotland, Wales and Northern Ireland each operate their own separate planning systems and building standards frameworks, with different permitted development limits, different exemption criteria, and different application procedures, so none of the England-specific figures here should be assumed to transfer directly. If you're in Scotland, Wales or Northern Ireland, the sensible approach is to check directly with your local planning authority or the relevant building standards body for the rules that actually apply, rather than relying on English guidance.

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