Permitted development rules for garden decking under Class E
Garden decking in England is governed by Schedule 2, Part 1, Class E of the Town and Country Planning (General Permitted Development) (England) Order 2015. Class E covers the provision within the curtilage of a dwellinghouse of any building, enclosure, swimming or other pool required for a purpose incidental to the enjoyment of the dwellinghouse — and the conditions of Class E directly apply to timber and composite decking structures. The key conditions for decking to be permitted development are: (1) the decking must not exceed 300mm in height above the natural ground level at its highest edge; (2) the total area of all outbuildings, enclosures and other structures (including decking) must not exceed 50% of the total curtilage of the dwellinghouse excluding the original house footprint; (3) the decking must not be forward of the principal elevation (i.e. not in the front garden visible from the street); (4) the decking must not be within the curtilage of a listed building, where permitted development rights are removed in their entirety for outbuildings and structures. These conditions apply to the structure as built, not the design intention — a decking structure that starts at 250mm above ground and then follows a sloping garden may exceed 300mm at the lower end, breaching the permitted development conditions at that point. A Lawful Development Certificate is recommended for any decking structure close to the 300mm threshold to provide definitive confirmation of PD compliance.
When does decking require planning permission in London?
Decking requires a full planning application in four main scenarios. First, when the decking platform height exceeds 300mm above natural ground level at any point on its perimeter. This is the most common trigger in London, where gardens slope away from the house (common on north-facing terrace gardens in hilly areas such as Highgate, Dulwich, Forest Hill and Crystal Palace) — a deck that follows the house floor level at 150mm can easily sit 500–800mm above the lower garden boundary. Second, when the combined area of all outbuildings, sheds, greenhouses, garages and decking on the plot exceeds 50% of the garden area (excluding the house footprint). Third, when the decking is forward of the principal elevation of the house (front garden). Fourth, when the property is a listed building or within its curtilage — all PD rights are removed for listed buildings, and any decking structure requires both planning permission and Listed Building Consent. Conservation areas, as discussed, may also restrict decking through Article 4 Directions if in force in the specific conservation area, though the GPDO Class E rights themselves are not automatically removed in conservation areas (unlike Class B for loft conversions). In practice, a rear garden deck in a conservation area at under 300mm is typically permitted development even within the conservation area designation — but always confirm with the local LPA.
Building regulations for decking: structural requirements and balustrades
The most common misconception about garden decking is that because it may be permitted development (not requiring planning permission), it is also outside building regulations. This is incorrect for raised decking. Part A (Structure) of the Building Regulations 2010 applies to any structure that could affect the stability of an existing building or that is used as a structural element. For a decking structure on posts with a finished floor level more than 600mm above ground, structural calculations are typically expected by building control to demonstrate that the post foundations, joist sizing, bearer spacing and fixings are adequate. Part K (Protection from falling, collision and impact) of the Building Regulations 2010 applies to any change of level exceeding 600mm — requiring a balustrade or guarding of minimum 900mm height. If the decking is at a level where a fall could cause injury (typically 600mm above ground or above), the requirement for guarding under Part K is absolute. The guarding must be designed so that a 100mm sphere cannot pass through any opening — ensuring child safety. For a deck with a change of level of 1m or more (common on sloped London gardens), the balustrade should be a minimum of 1100mm. Steps between the house threshold and the decking level must comply with Part K requirements on riser height (maximum 220mm) and going (minimum 220mm). Structural deck frames must be bolted, not nail-fixed, where the deck is more than 300mm above ground.
Timber vs composite decking: London specification considerations
The choice between timber and composite decking has significant implications for maintenance, longevity and cost in London's climate. Softwood (treated Scandinavian pine or European redwood) is the budget option at £30–£55/m² supplied and installed. Pressure treatment (often described as UC3 or UC4 rated) protects against rot and insect attack but requires annual oiling or decking preservative treatment to maintain colour and prevent surface weathering. Untreated softwood in a typical London shaded rear garden will start to show algae and greening within 12–24 months and significant surface degradation within 5–7 years. Hardwood decking (Ipe, Teak, Balau, FSC-certified Cumaru) costs £65–£120/m² supplied and installed. Hardwood is significantly more durable (25–40 year lifespan vs 10–15 years for softwood), resists splitting and warping better in London's wet-dry seasonal cycle, and weathers to an attractive silver-grey if left untreated. Composite decking (Trex, Cedral, Millboard) costs £80–£160/m² supplied and installed. Composite requires no maintenance, is slip-resistant, and does not rot, warp or splinter. Millboard's embossed-wood-grain composite is widely considered the premium specification in London garden design for its authentic timber appearance without the maintenance burden. For all decking in London, non-slip surface texture is critical — decking installed without anti-slip grooves or applied non-slip strips will become extremely dangerous in wet conditions, which describes the majority of London months.
