Engineering a Solution

Facing the Challenge

Modern specifiers have to contend with a variety of challenges when upgrading rooftop plant in existing buildings or planning out plant for new build projects. Increasingly congested rooftops in cities, not to mention delicate singly-ply rooftops and accessibility of plant, all have their own challenges that must be taken into consideration. Sam Birch, Technical Manager at Big Foot Systems, discusses the solutions available.

Short on space

With the UK’s highly populated cities continuing to expand, in over-congested areas such as London, the logical (and sometimes only) place to install mechanical plant and equipment is on the roof. Specifiers are therefore challenged with designing complex, busy rooftops with a mixture of plant and pipes that all need to be safely accessed at height. So what can consultants do to meet this challenge?

Complete one-off support and safe access solutions can be designed and fabricated for rooftops to specifically meet project requirements when a standard solution may not be suitable. For example, Big Foot Systems recently supplied a complete solution for rooftop plant support on a new commercial office building near Kings Cross train station in central London. Big Foot’s project team undertook site surveys and held several meetings with the principal contractor to design a solution for this large and multifaceted project, combining many different supports and access ways, so that the development met the needs of the customer.

Big Foot Systems

Big Foot Systems

This split-level project used a range of non-penetrative frames to provide safe access and support air handling units, chillers and high-level pipes. The size and complexity of this project proved to be a real challenge and involved designing a system with over 500 different parts to fit in an unusual space. This meant Big Foot had to be innovative and think outside normal design practices to provide a solution that worked well.

With this complex project, the plant area was split across two roof levels, level 9 and level 11. The supports for level 9 included: a custom non-penetrative Heavy Duty frame supporting an air handling unit (AHU) weighing over 7800kg, custom access to service the AHU, and integrated access and pipe support for seven large volume water pipes at 4m above the roof level. Meanwhile, supports for level 11 included: Heavy Duty Cubes supporting four chillers weighing 5,700kg each, two bespoke frames supporting AHUs weighing 6,500kg each, a custom Heavy Duty support with integrated access for a 15,750kg generator and over 100m² of custom safe access.

Keeping things accessible

Retrofitting cooling plant on busy roofs can prove tricky. Not only is it necessary to navigate existing rooftop pipework and equipment, it is also essential that the plant remains accessible for maintenance visits to ensure it performs efficiently. With a variety of obstacles and siting concerns to consider, an ideal solution is a non-penetrative plant deck.

Big Foot Systems recently supplied a custom plant deck to support a chiller on the asphalt roof of Manchester Royal Infirmary. The plant deck is located approximately 1m above the roof level to allow for pipe runs and comes complete with a custom platform around the whole perimeter of the chiller to provide access for maintenance. Big Foot also provided steps either side of the chiller, to enable access from both sides of the pipework, which saved the need for any step overs in another location.

Big Foot’s technical team used foot pressure calculations, UDL (roof load) figures and a wind summary to ensure the design was fit for purpose and was in line with the project’s requirements. The systems also benefitted from a wide base, making chillers stable in high wind locations, often a design consideration with very tall units.

Big Foot Systems

A delicate matter

Building regulations and modern methods of construction are driving the specification of single ply membrane roofs but their many benefits can be threatened if no consideration is given to the plant and equipment that may be housed on the roof and how to reach and install it. Single ply membranes are sensitive to footfall and, whether walking on the roof or installing plant, anything which cracks or punctures the waterproofing membrane can potentially cause leaks. Consultants are therefore set a tricky challenge when asked if provision can be made for installation of HVAC plant on a completed single membrane roof.

So what’s the answer? One solution to these installation headaches is to use non-penetrative, repeatable support structures that can be adjusted according to the demands of each individual project. For example, Big Foot Systems has developed its Light Duty and Heavy Duty modular framework systems which are ideal for installing AC units and heavier plant on flat roofs without damaging a delicate single ply membrane roof. Big Foot Systems recently supplied these non-penetrative supports to a shopping centre in West Yorkshire. A £260m development, the shopping centre totals 51,096m2 of retail and leisure space and has space for over 80 stores.

During the development, one of the main anchor tenants at the centre requested paving slabs to support the store’s air handling units (AHUs). However, the developer’s mechanical engineer understood the risks of using this method of support – placing slabs directly on a single ply membrane roof can tear through it, leading to destructive roof leaks and costly damage, often invalidating any warranty. Big Foot Systems was approached for its extensive technical knowledge and experience to provide a design that would safely and evenly support the plant loads without damaging the roof. Big Foot provided the anchor tenant with its HD Frames to support all AHUs as well as further supports for packaged plant rooms and AHUs at the shopping centre.

Big Foot Systems

Not only did the supports help protect the landlord’s roof warranty, but they also offer future benefits to the shopping centre since they can accommodate any planned expansion of the development. Big Foot’s non-penetrative design ensures that in the event of expansion, plant could be lifted and positioned on the new roof. Therefore, this type of design has the added bonus of saving time and labour costs on site with the potential to reuse the supports. The modular design means there is also the possibility to extend the frames, making it both versatile and cost effective.

With a wide variety of challenges on today’s busy and often complex rooftops, it’s essential that plant and pipework are safely supported whilst protecting the rooftop. Easily installed, repeatable, non-penetrative supports eliminate a whole range of problems associated with delicate rooftops as well as improving the safety of rooftop workers and offering the option of future alterations to the layout. The ideal choice for specifiers and building owners alike.

Big Foot Systems Ltd
Apex Way
East Sussex
BN27 3WA

+44 (0) 1323 844 355