Conservatory: do I need planning permission?

A conservatory is, in planning terms, just an extension made mostly of glass – and like any single-storey rear extension it is usually permitted development, so most conservatories go up without a planning application. The interesting question, and one we are asked often, is what happens when a conservatory stops looking like a conservatory: when you fit a solid roof, or build something large and permanent. This page covers the ordinary rules, and then that grey area in detail.

Is a conservatory permitted development?

Usually, yes. A conservatory is treated as an enlargement of the house under Class A of Part 1 of the GPDO – the same permitted development right that covers a brick rear extension. If it keeps within the Class A limits, no planning application is needed. In outline, for a single-storey rear conservatory those limits are:

• it does not extend beyond the rear wall of the original house by more than 3 metres for an attached (terraced or semi) house, or 4 metres for a detached house – or up to 6 and 8 metres respectively under the larger home extension prior-approval route
• it is no more than 4 metres high overall, and no more than 3 metres to the eaves where it is within 2 metres of a boundary
• the total area of ground covered by buildings within the curtilage, other than the original dwellinghouse, does not exceed 50% of the total curtilage area after excluding the ground occupied by the original dwellinghouse. Existing extensions and outbuildings therefore count towards the calculation
• it is not forward of the principal elevation, and does not include a veranda, balcony or raised platform
• the property is a dwellinghouse rather than a flat or maisonette; additional Class A restrictions apply on Article 2(3) land such as conservation areas, National Parks and National Landscapes, and listed-building consent is a separate consideration where the house is listed

These are the same limits as any Class A extension – the fact that it is glazed does not change them. What the glazing changes is the materials condition, which is where conservatories get their one special treatment.

The conservatory materials exemption

Class A comes with a condition (A.3(a)) that the materials used in the exterior work must be of a similar appearance to those of the existing house. Glass and white uPVC frames are plainly not similar in appearance to brick – so on the face of it a glazed conservatory ought to fail that condition. It does not, because the GPDO writes in a specific exception: the similar-materials condition applies to exterior work “other than materials used in the construction of a conservatory.” In other words, the glazed structure of a conservatory is expressly carved out of the materials rule. That single clause is what allows the classic glass-and-uPVC conservatory to be permitted development against a brick house.

What happens when you put a solid roof on it?

This is the question we are asked most. Replacing a glass or polycarbonate conservatory roof with a solid, tiled roof has become very popular – but it changes the planning analysis in a way that surprises people.

It does not automatically require planning permission. A conservatory with a solid roof is still an extension, and it can still be permitted development under Class A, provided it stays within all the ordinary Class A limits above. Adding a solid roof is not, by itself, a trigger for an application.

The materials point is more nuanced. Class A expressly excludes “materials used in the construction of a conservatory” from the similar-appearance condition, but the GPDO does not define a conservatory or say that fitting a solid roof automatically removes that exemption. A solid roof therefore does not, by itself, create a planning application requirement or automatically turn the structure into an ordinary extension for the materials test. The safest approach is to look at the structure as a whole and ask whether it still properly functions and reads as a conservatory. Where the answer is genuinely uncertain, a certificate of lawfulness for the proposed works can settle the planning position before work starts.

So the honest answer to “is it still a conservatory?” is that the label alone does not decide the planning position. A solid roof can still sit within Class A, and there is no statutory glazing percentage that automatically changes the answer. There is also a separate Building Regulations dimension to replacing a lightweight glazed roof with a solid one, particularly for structure and thermal performance, but that is a different regime from planning permission.

When does it stop being a conservatory?

This is the honest limit of the rule above, and it is worth being straight about: the GPDO never actually defines “conservatory”. The word appears in the materials condition but is left undefined, so there is no glazing percentage written into law that flips a structure from conservatory to ordinary extension. It is a matter of fact and degree, judged case by case.

The benchmark most often quoted comes from building control practice rather than planning: a conservatory is regarded as substantially glazed – broadly 50% of the wall area and 75% of the roof glazed. This is a useful yardstick, but treat it as exactly that. It is not in the Regulations for England and it is not a planning test, so no planning officer or inspector is bound by those figures when deciding whether something is a conservatory for the materials carve-out.

The line becomes important where the alterations are so extensive that describing the structure as a conservatory is no longer apt. Replacing large areas of glazing with solid walls, for example, may change the character of the structure so that the conservatory carve-out can no longer sensibly be relied upon. At that point the works need to satisfy the ordinary Class A conditions, including the similar-appearance requirement for exterior materials. There is no single statutory percentage at which that happens, so borderline cases are best treated as fact and degree.

When a conservatory does need planning permission

You are likely to need an application where:

• it is bigger than the Class A limits, or projects beyond the principal elevation
• the Class A 50% curtilage coverage limit would be exceeded once the ground covered by buildings other than the original dwellinghouse, including existing and proposed extensions and outbuildings, is taken into account
• the home is a flat or maisonette, which do not have these rights
• the property is listed – Class A planning rights and listed-building control are separate questions, and listed building consent is required where the works would affect the building’s character as a building of special architectural or historic interest
• the home is on Article 2(3) land, such as a conservation area, National Park or National Landscape, where Class A has additional restrictions. The right is not automatically removed simply because the land is designated
• an Article 4 direction has withdrawn permitted development for the area

What it costs, and confirming your position

If you do need to apply, this is a householder application. Fees are set nationally and change from time to time, so we do not quote a figure – see our guide to planning application fees. If you are unsure whether your conservatory – or a new solid roof on an existing one – is permitted development, a Lawful Development Certificate confirms it in writing and is useful evidence when you sell.

If the council refuses

A refused householder application can be appealed to the Planning Inspectorate, on the tighter householder appeal timetable. Our guide to planning appeals explains the deadlines and how it works.

Should you just build it?

For an ordinary glazed rear conservatory within the Class A limits, a planning application will often not be needed. Replacing a glazed roof with a solid roof can also remain permitted development, but the answer depends on the works staying within Class A and, where the conservatory materials exception is being relied upon, whether the altered structure can still properly be regarded as a conservatory. There is no statutory glazing percentage which settles that question. The time to check carefully is where the structure is large, forward of the house, on Article 2(3) or listed land, at a flat, or where the alterations substantially change the character of the conservatory. A Lawful Development Certificate can provide certainty before work starts.

Other Common Projects

Conservatory Planning Permission Page Updated: 2nd September 2026