In England a “raised” platform is one with a height greater than 0.3 metres; the permitted development rules for enlarging a house, which cover a conservatory, do not allow the enlargement to include a verandah, balcony or raised platform, while garden decking that is no more than 0.3 metres high can be permitted development under the separate Class E rules for outbuildings and structures.

Why a raised terrace matters for a conservatory project

Many conservatory projects include a terrace, decking area or step-up platform outside the new doors. Under the planning rules in England a conservatory is usually built as an enlargement of the house under Class A of Part 1 of Schedule 2 to the Town and Country Planning (General Permitted Development) (England) Order 2015. That class contains a specific exclusion for raised platforms, so an outdoor area that is part of the same works can take the whole scheme outside permitted development even when the conservatory itself would otherwise qualify. This guide covers England; Wales, Scotland and Northern Ireland have their own rules, covered in our guides to Wales and Northern Ireland.

What Class A says

Paragraph A.1(k) of Class A provides that development is not permitted if it would consist of or include the construction or provision of a verandah, balcony or raised platform, the installation, alteration or replacement of a microwave antenna, a chimney, flue or soil and vent pipe, or an alteration to any part of the roof of the dwellinghouse. The interpretation provisions for Part 1 define “raised”, in relation to a platform, as a platform with a height greater than 0.3 metres. The government technical guidance for householders says verandahs, balconies and raised platforms are not permitted development and will require planning permission, and that a raised platform is any platform higher than 0.3 metres and includes roof terraces.

How height is measured

The technical guidance explains that references to height are measured from ground level, meaning the surface of the ground immediately adjacent to the building. Ground level does not include an addition laid on top of the ground, such as decking. Where the ground is not uniform, for example on a slope, it is the highest part of the ground surface next to the building.

Decking under Class E

The technical guidance says Class E, which covers buildings and other structures in the garden area for purposes incidental to the enjoyment of the house, restricts the height of raised platforms, and that Class E allows garden decking provided it is not more than 0.3 metres high. The guidance describes “building” as including any structure or erection, and lists garden sheds, storage buildings, garages and garden decking as examples that can qualify if they have a purpose incidental to the enjoyment of the house. Class E limits also apply, including that the total area covered by buildings, enclosures and containers in the curtilage, other than the original house, must not exceed 50% of the curtilage, and that no part may be forward of a wall forming the principal elevation. Our guide to the 50% garden rule explains the coverage limit. The guidance also notes that buildings attached to the house are not covered by Class E and fall under Class A.

What this means for a conservatory scheme

Putting these points together, a low deck that stays at or under 0.3 metres and meets the Class E conditions can be permitted development, whereas a platform above 0.3 metres, or a raised terrace that forms part of the works enlarging the house, falls within the Class A exclusion and needs planning permission. Article 4 directions, listed building status and conservation areas can remove permitted development rights; see our guides to Article 4 directions and how permitted development works for conservatories.

Applying for permission

If a scheme includes a raised platform, the routes are a householder planning application, covered in our guide to householder planning applications, or redesigning the scheme so the platform is no higher than 0.3 metres and the other limits are met. The Planning Portal states that its guidance is introductory and based on national rules, that local rules may also affect what permission is needed, and that householders should check with their local planning authority. A lawful development certificate can confirm that a scheme is permitted development, as explained in our guide to lawful development certificates.

FAQs

How high can decking be before I need planning permission in England?

The technical guidance says Class E allows garden decking provided it is not more than 0.3 metres high. A platform higher than 0.3 metres is a raised platform.

Does a raised terrace next to a conservatory need planning permission?

Under paragraph A.1(k) of Class A, development that includes a raised platform is not permitted development, so planning permission is needed.

How is the height of a platform measured?

From ground level, meaning the surface of the ground next to the building, excluding decking laid on top, and the highest part where the ground is not uniform.

Do these rules apply in Wales?

The Planning Portal says its guidance relates to England and that the policy in Wales may differ.

The bottom line

In England a platform higher than 0.3 metres is a raised platform, and including one in works that enlarge a house takes the scheme outside Class A permitted development, so a conservatory with a raised terrace needs planning permission. Low decking of 0.3 metres or less can be permitted development under Class E if its other limits are met. This is general information, not planning advice; confirm the position with the local planning authority.

Sources

This guide draws on the following primary sources, current as of 24 September 2026:

• legislation.gov.uk, “The Town and Country Planning (General Permitted Development) (England) Order 2015, Schedule 2, Part 1: Development within the curtilage of a dwellinghouse”
• GOV.UK, “Permitted development rights for householders: technical guidance”
• Planning Portal, “Planning permission for extensions”

Related guides

Compare Conservatories is an independent guide. We may earn a fee from some links; this never affects what we write. This article is general information, not legal or planning advice on any specific property — always confirm requirements directly with your local planning authority.