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As countless people in the construction industry will readily acknowledge, knowing the Building Regulations inside-out is no guarantee that the progress of a project can be navigated without obstacles. Below the surface of official legal compliance, there are often undercurrents of preferred practice which architects and developers need to be aware of and follow with equal diligence to meet the approval of key stakeholders. This kind of non-statutory regulation has recently caused an evolution in the design and specification of balconies. It has largely been driven by housebuilding warranty providers and concerns three specific requirements: fire resistance, drainage and design life.

[please note: since this article was written in 2017,  the government has introduced new Building Regulations relating to fire safety on balconies – read our full overview here]


The external spread of fire on multi-storey buildings became part of the national conversation following the Grenfell disaster, but a year earlier the issue had already been touched upon when BRE Global published research in its ‘Fire safety issues with balconies’ document. It reported 24 balcony fires since 2005. The most common causes were arson, disposal of smoking material and misuse of barbeques. The report also stated that “the presence of a balcony can offer residents an alternative means of escape in a fire event if their main exits from the dwelling are inaccessible. Even if not by design a balcony can provide a refuge area for occupants to await rescue from Fire and Rescue Services for which there are numerous documented cases.”

The inference is clear:  measures to prevent the outbreak and spread of fire on balconies are potentially life-saving. This point has not been lost on warranty providers and they have become increasingly strict in their stipulations relating to fire risk. Most of them prohibit the use of timber joists and frequently reject the use of timber decking. Wood-polymer composite decking is often disapproved too; likewise glass reinforced plastic (GRP) flooring, an oil-based product containing organic compounds which burn. As a result, architects are increasingly using emerging alternatives such as aluminium decking, which has a Class 0 Fire Rating (the highest possible fire resistance score).

Steel is the preferred substitute for timber joists and this brings further implications to the design and specification of balconies. Extensive steelwork is expensive and it makes economic sense to reduce the amount of required support by using decking that is lightweight yet high in load-bearing capacity.  The structural efficiency of aluminium decking is ideal in this respect – joists are only required at 2000m centres compared to around 450mm for most composite decking.

Drainage is another design feature which is becoming more structurally efficient at the behest of warranty providers. Any balcony with a floor area of over 6m2 is conventionally fitted with ‘positive drainage’ – a term which refers to a catchment tray which is fixed directly below the balcony flooring and usually encased within a soffit. Also requiring a hopper and drainpipe, it’s a cumbersome solution which adds substantial weight and time to the installation. It is also prone the build-up of dirt, sediment and various waste substances which carry the attendant risk of blockage.

This has prompted warranty providers to seek alternatives. An increasingly popular option is an eaves drop system that allows rainwater to fall freely to the ground. This can be achieved with open grille balcony flooring. As an optional modification, rubber inserts can be placed between the grille bars to create a closed construction which drains water from one edge with the assistance of a slight slope in the grille panel installation. In either case, the absence of a conventional catchment tray and pipe requires an alternative way to facilitate the disposal of water without threatening the building. This is usually provided in the form of a French drain (named after its 19th century inventor Henry French) at ground level. This system comprises a slightly sloped trench which is filled with a layer of pea gravel above a perforated pipe which sits at the bottom. Surface water and groundwater seeps between the gravel and travels freely through the pipe. It’s a fast and efficient way to divert water away from the building and prevent saturation or pooling.

The combination of grille balcony flooring and French drain is a lighter, more economical solution which is quicker and easier to install. As a result the traditional method of positive drainage is showing a negative trend in popularity.

The third key stipulation concerns every element of balcony design: certain warranty providers are now insisting that all components and materials have a minimum design life of 60 years. This level of longevity is hard to achieve with timber or GRP, but aluminium is far more durable. It is widely considered to have a design life of 60-100 years but one report has suggested that it has an infinite lifespan in internal installations and a minimum lifespan of 120 years in external installations.

Whilst fire safety, drainage and design life have experienced the most significant shifts in recent years, a fourth design element is increasingly important to consider: slip resistance. It’s an area of performance which has come under greater scrutiny and in many cases balcony flooring is now assessed for slip resistance before being signed off. The Pendulum Test, which measures dynamic coefficient of friction, is the HSE’s preferred method of testing, largely because it is portable and a reliable indicator in conditions where slips commonly happen. It is advisable to develop a balcony specification with reference to the Pendulum Test as it reveals significant differences between specific materials and products: for example, in wet conditions aluminium decking with a specially engineered anti-slip surface is more than twice as slip resistant as wood-polymer composite decking. If anything, this calculation is a conservative estimate of the difference in actual conditions as it does not take account of moss, slime and mould which regularly affect wood and wood-based products if they are not regularly maintained.

In all areas of balcony design it is invaluable to stay conversant with prevailing guidance and develop specifications accordingly. Many developers only become aware of certain requirements when the stakeholder intervenes at a later stage, adding delay and cost to the construction programme. By consulting with the relevant warranty provider at an early stage, architects can avert a potential collision course and chart a smoother journey for their project.