Balcony Decking Selection Guide for Architects and Specifiers
Following a number of notable balcony fires and the Hackitt report, Approved Document B was changed in November 2018 (and also as amended in December 2019 and April 2019) in that balconies must now be made from materials of limited combustibility. The MHCLG followed this up with advice that culminated in January 2020, advising building owners that the removal and replacement of any combustible material used in balcony construction is the clearest way to prevent external fire spread from balconies. This creates not only a challenge for Architects and specifiers to create designs to meet these new technical requirements, but also to achieve the appearance and feel that is expected in a space that is often an extension of the home.
There are key decisions that need to be made in the selection of the appropriate finish, these are set out in the following section.
Free Draining or Drained
Free-draining is used to describe the design where rain falling on the balcony can fall between the decking boards. Free draining balconies need to have a gap between the decking for the water to drain through. Free draining balconies don’t usually have soffits, so this can reduce the cost, but it is important to consider what the decking will look like from underneath as this will be readily visible. Neat bearers and boards that are attractive from the underside also is important. Its also important there aren’t too many small crevices that birds or insects can nest in.
Drained balconies can be either surface drained or via a lower drainage layer beneath the decking, this can be either via a soffit that catches the water or, an impermeable structure to the balcony itself (such as precast concrete). With drained balconies, it is important to ensure that the waterproofing extends up the facade at least 150mm from the drainage layer (at least 75mm at doorways). The selection of the waterproofing must be carefully checked against the requirements of Part B of the building regulations.
Whilst achieving the right appearance is important, it is also important to choose a balcony finish that fulfils the performance requirements:
- FIRE: Must be A1 or A2-s1 d0 as classified by EN 13501. Note that this applies to EVERY component of the system (i.e including any pedestals, or fixing clips).
- STRENGTH: Must have the required strength for the application. The strength is tested via the application of a distributed load, but also a point load at the support centres that you wish to use. The use class of the balcony or terrace will determine the distributed load and point loads that need to be achieved.
- SLIP POTENTIAL: Slip potential must be considered and be suitable for the application. PTV vales are used to assess this. Refer to the HSE website for more guidance on this.
- THERMAL EXPANSION: The material that the decking is made from will determine the thermal expansion. Aluminium has a coefficient of thermal expansion of 24×10-6m/mK. This means that for example a 3metre section of aluminium will get around 3mm longer at 40°C than it is at 0° If this is not accounted for in the fixing design, the fixings can break. Calcium silicate composites can have a coefficient of thermal expansion of 13×10-6m/m. So, expansion gaps can be smaller.
- SCRATCH RESISTANCE: It is common for balconies and terraces to have furniture placed on them. Ensure that scratches don’t become a problem during construction or during the lifecycle of the structure.
- WEATHERING PERFORMANCE: Make sure that any materials specified have had the material and coating tested for longevity. This can be carried out by accelerated weathering testing. Where the material is subjected to a cycle of UV, freezing and thawing actions to simulate an appropriate number of years.
- LIGHTNING PROTECTION: Any conductive elements must be considered as part of the risk assessment conducted for lightning protection in accordance with BS EN 62305.
- HEAT BUILD-UP: Especially if the balcony or terrace will be accessed barefoot, it must be considered that the surface should not build-up too much heat such that it could cause burning. Metal surfaces generally heat up more in the sun than other materials.
- NOISE: The surface must not generate excessive noise from wind, rain and hail.
There are a range of materials available, by considering the key performance factors, it the best material for the application can be selected, and will perform for the long term.