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With scaffolding systems that fully encapsulate a building becoming increasingly common, the onus is on everyone in the sector to understand the requirements for the design of temporary roofs. Paul Thompson reports.

 

As the country gets battered by the latest winter storm, sites large and small sound to the rattle and ripple of wind-blown sheeting on temporary scaffold roof systems.

These additions to the scaffolding world have become commonplace on construction sites up and down the country as clients and contractors try to limit the number of days lost to the elements on projects by providing some shelter for workers.

But with that increase in popularity there follows an increase in responsibility. It is imperative that contractors understand the importance of ensuring these temporary roofing systems are adequately designed to fit every application.

“I am surprised that temporary roofs have not been used more in the past. However, in recent years they have become increasingly popular. As an industry, we need to make sure everyone – client, main contractor, designer and scaffolding contractor – is up to speed with their design and installation,” says Robert Candy, chief executive of the Scaffolding Association.

Increase in demand

That move toward the specification of temporary roofing is thanks largely to a desire from clients, according to industry expert and PB Scaffold Design managing director Phil Barber. The push to build quickly, safely and accurately has seen demand for temporary roofs – and their design – increase.

“Over the last four or five years, we have seen a shift. It used to be just the larger projects, but now we see temporary roofs on all but the smallest of residential projects,” he said.

That increase in demand is tied into an increase in complexity over standard scaffold that can challenge even highly experienced scaffolders. With plenty of areas of design influence to consider, many find that they need to go back to the drawing board or bring in specialist designers to ensure the temporary roofs are fit for purpose and that they comply with all the latest guidance and legislation.

Design factors

“Generally, scaffolding systems are not the most complex to design. Unfortunately, temporary roofs are not quite as simple. You have to design them to similar tolerances and loading as those of a permanent building,” explained Chris Harrison, director at Apex Scaffold Design.

He highlights a raft of influencing factors that can all affect the final design, from the type of roof cover (plastic sheeting or corrugated steel) to the fixing of the scaffold (kentledged or tied). Other factors include the type of scaffold being used (tube and fitting or system scaffold) even down to the lifting operations and whether the scaffold supporting it is sheeted or unsheeted.

Mr Harrison added: “There are so many points to consider – there is no generic design for a temporary roof. These are complex structures and need to be designed as such.”

It is a point echoed by Rory Brady, principal design engineer at Node Scaffold Design. He points out that although these roofing systems are labelled ‘temporary’, they can in fact be anything but. The fluctuating fortunes of an average construction project can see the roof remain in situ for several months and often years as complications arise.

“We all know construction projects can often overrun, that’s the nature of them, but if that happens, is the temporary roof and scaffold design still valid? Has it been designed to work throughout the seasons and with the different loading that can be brought onto the structure?” he questioned.

That can depend on the size of the scheme and the awareness of the project team. On larger projects the likelihood is that the scaffold design, including that of the temporary roof, is properly controlled to accommodate any fluctuations, including those introduced post-design as the project advances. Even the simple act of cutting a section out of the scaffold sheeting to ease in supplies can significantly affect its overall performance.

Here is where contractors and clients need to be vigilant if they are to comply with health and safety legislation, CDM regulations, and keep the structure, workforce and general public safe.

“Clients and scaffolding contractors need to understand just how much the loading on a temporary roof can change throughout a project. Cutting holes in scaffold sheeting or even removing windows and doors or altering the layout of the building can all have a dramatic effect on the capability of the temporary roof design,” explained Mr Brady.

Early considerations

Of course, all this extra design input has a cost implication. Clients need to be aware that one of the reasons a scaffolding quote from one firm might be much higher than that of another is that it has factored in design costs, rather than left them out.

But, Mr Brady argues, some of that cost can be mitigated by bringing in a designer at the earliest stages of a scheme.

“In the end, you get what you pay for and greater design input will be reflected in greater project costs,” he said, adding, “The use of temporary roofs is often a last-minute decision and that is where there can be an issue for a contractor.

“But bringing specialists in as early as possible means designers can incorporate any requirement from the get-go. They know exactly what is required and when. It makes sense.”

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