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Balcony and terrace decking selection guide for architects and specifiers from Blazeboard

Balcony and terrace decking selection guide for architects and specifiers from Blazeboard

Changes in regulations and guidance has changed the decision framework within which Architects and Specifiers shall select appropriate finishes for balconies and terraces.

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. In addition, renewed guidance on balcony design is provided in BS 8579.

Further, the renewed technical requirements and recent events mean that more than ever, balconies and terraces are vital outside areas of the home. Therefore, it is important that finishes are suitable for the home environment.

This document includes specific factors related to the material performance of the decking material which can assist with choosing the right material for your project.

Material Performance

Whilst achieving the right appearance is important, it is also important to choose a balcony finish that fulfils the performance requirements:

FIRE: The balcony or terrace finish 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. For example, residential balconies for a single-family dwelling have a use class A5 as defined by the UK National Annex of Eurocode 1. This specifies the loads as 2.5KN/m2 distributed load, and a point load of 2KN.

SLIP POTENTIAL: The HSE has determined that Pendulum Test Values are a reliable method of determining the risk of slipping in dry, wet and contaminated conditions. There are two types of slider used, and due to the potential for users to be barefoot on balconies and terraces, it is important that both test methods are used and results checked in these scenarios. The pendulum test values are considered as set out in Figure 3, alongside other relevant factors.

Other relevant factors can include contamination, and ageing effects. Also, it is common for flooring to use ribs or grooves to improve slip resistance. Consideration should be given to whether these can actually harbour dirt, moss growth and ice and potentially make the slipperiness worse in use.

THERMAL EXPANSION: The material that the decking is made from will determine the thermal expansion. Aluminium has a coefficient of thermal expansion of 24x10-6m/mK. For example, this means a 3metre section of aluminium will get around 3mm longer at 40°C than it is at 0°C. 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 13x10-6m/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. Scratches can look unsightly, but also can initiate corrosion.

WEATHERING PERFORMANCE: Make sure that any materials specified have had the material and coating tested for longevity. For example, materials can chip or shatter from frost interaction. This can be checked 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. The installation should replicate the tested scenario. For example, where the material relies on a surface coating for corrosion resistance, care must be taken during installation that this coating remains intact.

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 when exposed to direct sunlight 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 and when walked on. Make sure that none of the components can rattle.

CREVICES: It is important to consider the underside of the balcony finish. Crevices can create a haven for wasp nests and insects. Any channels or ledges to the underside of the finish should be closed off.

By considering these key performance factors, the best material for the application can be selected, that will perform for the long term.

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