Central Manchester University Hospitals NHS Foundation Trust

Project: Central Manchester University Hospitals NHS Foundation Trust

Blezard Design & Consult, Building Services Consultants, Preston were recently faced with a very difficult challenge, how to support new Air Handling Units and air conditioning equipment on an ageing flat roof in poor condition. Over many years the roof of the University Dental Hospital, Central Manchester University Hospitals NHS Foundation Trust had been used to place external building services equipment and the space had subsequently become littered with numerous pieces of old equipment, along with what some would say were potentially dangerous obstacles which over time have been weatherproofed into the structure. The roof space bears all the scars of old concrete plinths, flagstones, rusting steel beams and gantries, etc., The roof itself suffers from poor drainage and the effects of ponding….standing water degrading the weatherproofing and becoming extremely slippery due to the icy conditions in December.

This was an interesting challenge, not only was it necessary to devise a system to support an AHU weighing 1947kg, but there were numerous air conditioning and fan units to be supported in amongst. Ramped safe access platforms were required for future access and possible roof repairs. Accessibility for maintenance of both new and existing building services equipment was paramount; a smaller AHU is positioned in an otherwise inaccessible adjacent area.

The scheme called for a custom anti-slip access platform incorporating steps, handrails and also custom built ramps to make it possible for M & E operatives to roll building services equipment across the roof area in future. The solution, to provide non slip integrated modular AHU and AC unit supports with associated GRP ramps and platform access designed to target adjacent door and window cills, whilst also providing safety during the installation for M & E contractors working in close proximity to parapet walls beyond which are drops of three stories.

Big Foot Systems specifications team provided ongoing technical support to the design consultants and mechanical services sub-contractors to help devise an integrated custom plant support and access walkway system. Earlier designs had ultimately proved unworkable because of the large number of roof obstacles and also because of restricted roof space. Big Foot’s integrated design solution allowed for the larger AHU to be supported independently of its associated platform for a period of three weeks over the Christmas holidays. Supplying the AHU freestanding frame ahead of time meant the AHU could be craned onto the roof on the scheduled date. Big Foot integrated platforms would be supplied after the Christmas holidays. This meant that consideration had also to be given to the AHU and its freestanding support frame remaining stable in the event of any high winds and until the assembly benefitted from the additional mass of the platforms which would follow later. Big Foot wind loading analysis proved that the partially installed assembly would remain stable in the event of any high wind loads over the Christmas break while the associated platforms were being custom fabricated.

Working closely with Blezard Design & Consult and T Jolly Services Ltd of Preston, Big Foot technical team submitted initial design proposals and also fully evolved drawings showing angles of handrails, position of steels and legs to show that Big Foot proprietary support legs and bases could be landed correctly between the numerous obstacles.

Big Foot Specifications Manager Mike Smith comments: “the initial design concept looked pretty straight forward on paper but as is sometimes the case, particularly with access platforms, the reality often proves more difficult to achieve. Right from the off the first thing we had to do was consider how to make it as easy as possible for the contractors to carry everything up a staircase and onto the roof, clearly we had to go with a modular system having manageable component sizes. At each step along the way our design team provided drawings and technical assessments for approval by the consultants to highlight some of the potential difficulties being faced on site by the sub contractors. Changes to the original concept became necessary and despite some initial reluctance from the design team Big Foot proposals achieved a practical and affordable solution. The consultants agreed to modify their earlier designs and subsequently added a large rectangular platform which we were also able to integrate into our design. Hitting critical target heights around door cills and window ledges, and achieving critical angles to span two access ramps proved especially difficult due to the limited roof space, but all these difficulties were successfully overcome. There are ongoing concerns about the condition of the roof and the likelihood of roof repairs being needed sometime in the near future and so consideration was given to the roofers need to gain access beneath the services equipment and access walkways in order to undertake repairs or possibly even renew the roof completely. During the design process we did everything possible to allow for the easy removal of individual platform anti-slip sections and also individual feet and adjustable legs should roofing contractors ever want to gain access to the weatherproofing membrane. Being a medical facility any decommissioning of the various building services equipment to undertake roof works would prove hugely disruptive apart from being extremely costly”

During the installation period Big Foot Technical Manager Laurence James prepared detailed production CAD drawings and also assembly and installation drawings for the subcontractors. To help speed the installation process along Big Foot also attended site several times during the installation period to support the M&E installation team.

Big Foot distributors Jack Pennington supplied the assemblies, Stuart Wilson later commented: “although the contractors procurement team felt the project had taken longer than had been originally envisaged by the clients design team, they were nevertheless very happy with the outcome.”

T.Jolly Services Ltd, Project Engineer Paul Birley stated: “the original design solution was workable but required specialist input to overcome the various issues that you encounter when installing new plant and services to an existing building. Our procurement department introduced Big Foot Systems as our specialist, through close collaboration between the construction team, specialist and site operatives we have achieved a satisfactory solution that meets the project requirements and future maintenance issues”.