Low garden decking can be permitted development for a house where the relevant conditions are met. Raised platforms, external balconies and roof terraces generally need planning permission. The structure, access and guarding must also be assessed; a planning decision is not confirmation that an existing roof or deck can safely carry people. [1] [2] [3]
When is garden decking permitted development?
Planning Portal's householder guidance identifies a maximum height of 0.3 metres above ground level for decking relying on the relevant permitted development provision. It must also meet the other restrictions, including its position relative to the principal elevation and the limits on the amount of the curtilage covered by additions and other buildings. [1]
The government's technical guidance defines a raised platform as one higher than 0.3 metres, and includes roof terraces within that term. The curtilage coverage calculation is not simply half the visible lawn: the original house's footprint is excluded from the area used for the relevant calculation. [4]
These householder rights do not apply to flats and maisonettes. Also check listed-building curtilage, designated-land restrictions, Article 4 directions and planning conditions before relying on a low platform's height alone. [1] [4]
Balconies and roof terraces
An external balcony with a platform is generally not permitted development. A Juliet balcony, without an external platform on which to stand, may be treated differently, but the associated window or door alteration still needs its own planning and building regulations checks. [2]
A roof terrace should be assessed as outdoor accommodation, not described merely as a flat roof. Planning considerations can include overlooking and privacy. Discuss the actual intended use and access with the designer before spending money on railings or terrace finishes. [2]
Does building control need an application?
Most new balcony construction engages building regulations, including the supporting structure and protection from falling. Existing construction also needs to be suitable for the additional loading. Building control and planning assess different matters, so success under one system does not establish compliance with the other. [3]
There is a distinction between a change in how an existing roof is used and controlled building work to make it usable. LABC explains that a new access opening, structural strengthening or a change affecting escape can bring building regulations into the project even where the use of the roof alone would not require an application. Check the full scope. [5]
Have the existing roof or support assessed
A roof designed only as a roof should not be assumed suitable as occupied outdoor space. Ask the structural engineer to assess the proposed loading and the supporting construction, including any strengthening. Adding furniture or finishes is not evidence that the original structure was designed for that use. [5]
The design also needs appropriate guarding, safe access, weatherproofing and relevant fire performance. Resolve the junction between a new access door and the roof covering as part of the design, not as a last-minute adjustment after the terrace level has been set. [3]
A practical sequence is to establish the planning route, survey the existing structure, coordinate the access and safety details, and agree any building control application before construction. Do not order a standard balcony kit as a substitute for checking the building to which it will be attached. [2] [3]