The company is part of the Forbes-Wilson Group, and the Forbes-Wilson family has been around cranes and rigging for well over 50 years. But crane manager Peter Saunders notes that the procedure for building the roof on the ground and erecting it in a multi-crane lift has been refined with input from shed designers and builders and a range of other people involved in the industry.Building the roof on the ground has many advantages. Most importantly it is safer, as fewer people are working at heights, for less time, and can generally work from an elevating work platform. The roof sheeting is also installed on the ground, although it is left unsecured where lifting slings need to penetrate the roof to attach to the roof trusses. There is one sling for each truss, and cranes can support multiple trusses, depending on their capacity. Spreader beams ensure that the weight is spread evenly but it also requires careful monitoring to ensure that the roof is being lifted evenly in a multiple crane lift (lifting is staged, and levels are checked and corrected after each stage). Up to six cranes have been used for large roof areas.Often insulation, wiring for lighting, external gutters and even ducting for ventilation are installed before the lift. A further refinement is that the columns are attached to the roof trusses by a single bolt, allowing them to swing into a vertical position as the roof is raised. When there is sufficient clearance, the columns can be attached to the footings, and a second bolt is installed at the top of each column to hold it rigid.In practice the roof is easier to lift with the columns attached, as the friction with the ground as the roof is being raised, combined with the weight of the columns themselves, tends to hold the roof steady and make it less susceptible to movement from wind gusts. Even when the legs are raised clear of the ground, it is possible to lower the roof slightly to stabilise it if there is a gust of wind.The success of the method is such that virtually all the major shed builders in the region, as well as other crane hirers in the region, have adopted the method. There are even variations of the method, to suit different site conditions. Normally all the cranes stand outside the roof when undertaking a lift, but on some sites the building is too close to the perimeter of the block to allow a crane to stand outside the roof. In those instances there is a cut-out section of the roof that is filled in after the roof has been erected. The purlins are left out of a bay, allowing an all terrain crane (chosen for its narrow outrigger spread) to drive into the bay. The purlins and roof sheets are filled in behind the crane, which drives out once the roof has been lifted and secured. From a pure crane hire point of view, the method involves less hire time than traditional stick erection. It also involved a considerable investment of time in educating the market about the benefits of the method, prior to it becoming accepted practice. However, the Forbes-Wilson Group believes that by doing the right thing by its customers, it will generate loyalty and repeat business, and keep its cranes busy. It seems to be working out that way.
