Building façades are designed as high-performance elements demanding practical, economical and effective maintenance. Façade access is an important part of a building’s maintenance and is a highly specialised service with very limited expertise available globally within the construction industry.
Façade maintenance tasks range from regular cleaning of the glazing to significant replacement of failed panels. Once the options to avoid working at height, set out in the working at height hierarchy, have been exhausted, the required access can be gained by using temporary or permanent façade access equipment (FAE). Operatives using FAE are exposed to the hazard of falling from height because of things such as:
The options for access are from the top down or bottom up. For low rise developments of up to 40m, Mobile Aerial Work platforms can be employed providing sufficient consideration is given to the landscaping to allow the machines area to work. Above this height, top down building maintenance units (BMUs) are more suitable.
Generally, roofs are utilised for mechanical, electrical and plumbing (MEP) services which are positioned centrally around the core. This allows short reach lightweight BMUs along the roof perimeter. Centrally located BMUs can be used if the roof is used as a communal space or if the BMU loading needs to be imposed on the stronger parts of the building cores.
Coverage on buildings with complex façades can be a particular problem, regardless of the BMU’s position. Sky bridges create a dead area similar to that found with balconies and twisting facades can be challenging. Counterweighted cradles for underhanging areas and separate systems for inset areas add weight and cost to the machines or additional systems to the building. The challenges caused by complicated facades increase when adding glass replacement into the equation.
To replace the glazing or other sections of the façade, an increasingly common option is to use the BMU with the facility of an auxiliary hoist, in addition to the cradle for the operatives. (Note: Total suspended load on glass lifting winch is limited to 1 ton as per BS EN 1808).
Once glass has been installed it will generally last beyond the lifetime of the building unless subjected to an external force. After practical completion of a building, it’s relatively rare for individual panes of glass to break. Warranty failure is a more common reason for panels to be replaced.
In general operation the cradle of the BMU will lightly touch the façade unless an external force is placed upon it. In normal operation the only external force will be the wind. The use of the cradle is limited by the wind speed. Equipment shouldn’t be used if the wind speed is likely to exceed 12m/s (25 mph) which is equivalent to a Force 6 (strong breeze) on the Beaufort scale.
On the weather side of the building, the suspended platform will be held against the façade and the wind loading will be the same. On the lee side, the cradle is shielded from the wind. The building sides have the most risk, but the suspended platform is presented end on with its smallest profile. The lee corners of the building can be the worst points as a rotor. Solar shading fins, louvers and brise soleil can also pose problems with the loads on them being localised.
The effects of ‘in-service’ and ‘fall arrest’ (overload / overspeed / accidental) loads imposed upon the building structure from the operation and storage of façade access equipment are significant. They should be coordinated with the structural engineers throughout the design process.
Load paths through the structure should be accounted for when evaluating the reactions of the façade access systems in all its operational and stored positions when fully loaded.
Equipment connections to the structure should be welded, bolted, or cast in place. The attachment method should be defined during early design stages so that correct provision to periodically inspect the fixings are integrated within the roof finish.
Safety and stability factors are determined by local codes and industry standards and should be incorporated in the design calculations of the access equipment and building structure. This is particularly important for steel structures due to the possibility of beam torsion and the necessity of additional reinforcing steel in those areas. BS EN 1808 recommends the BMU specific factors be applied to the design loads for the superstructure.
TÜV SÜD are specialist consultants in façade access systems and can help with the most demanding projects across various sectors including Retail, Commercial, Leisure, Healthcare, Education, Industrial and Residential. We have a wealth of experience working on an enviable portfolio from small-scale projects to major iconic developments. Please visit our façade access system web pages for more info or contact our team, who will be happy to discuss your project. For the latest insights and updates, sign up for our email newsletter.
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