Summary
¦ The local authority planners requested that the store roof be curved.
¦ DTE made 44 barrel-vaulted trusses and two OSB spandrel panels.
¦ The roof was fitted by local company Paul Martin Joiners.
¦ The installation was completed in five working days.

When Donaldson Timber Engineering (DTE) was asked to supply an unusual, curved roof for a Tesco Express store in Dunfermline, Scotland, it didn’t hesitate in accepting the work.

“A curved roof is not something you see very often,” said DTE’s special product manager, Rodger Cook. “Usually Tesco Express comes as a prefabricated unit with a flat roof but on this occasion, because of the area where the store was going to be, the local authority requested in the planning it should have a curved roof to make it stand out. They were keen to use the building’s form and shape to highlight its presence among the locale, where a flat-roofed building may have been overlooked.

“Supplying a curved roof was a first for us, and certainly different from any other project we’ve worked on,” said Mr Cook.

But when contractor Bowmer & Kirkland approached DTE, the engineered timber specialist had the solution.

“The logical response to meet the design criteria was using timber roof trusses which are flexible, economical and quick to erect, so Bowmer & Kirkland approached us for a quote,” said Mr Cook. “We priced for supply only originally but the surveyor asked if we could do a supply and fit job instead. Happy to oblige as best we could, and knowing that we had plans in place should this situation arise, we agreed to supply and fit the roof – another first for DTE.”

DTE designed, manufactured and supplied the roof as normal, and local joinery company Paul Martin Joiners fitted the roof on DTE’s behalf.

To make the curve, DTE manufactured 44 barrel-vaulted trusses with 14m spans, and two barrel-vaulted OSB spandrel panels. The trusses were set 1.2m apart and the top of the trusses were made from shorter lengths of timber to create a faceted truss, with incremental height differences to create the gentle curve. The structural frame was then sheeted with 18mm plywood with metal legs attached to it, which were inserted into the top of the trusses. Finally, metal sheeting was attached to the plywood, which formed the distinctive smooth curved roof.

Fire break requirement

In order to meet the project specification, DTE also had to install a fire break into the centre of the roof.

“To meet the building requirements we made a truss with fire Rockwool attached to both sides of it. This provided the roof with a one-hour fire break,” said Mr Cook. “At DTE, we pride ourselves on being able to supply more than just the roof trusses for every project. We also provide the ancillary products to meet all our customers’ roofing requirements. In total for this project, we supplied all 44 trusses, the two spandrel panels, 16 gable ladders split into short sections, plywood and the fire Rockwool.”

All the roof elements were factory manufactured at DTE’s Buckhaven branch, delivered to site, and lifted into place quickly and simply. The trusses were craned into position, set out at 600 centres and braced with 22×100 timber. The spandrels were then lowered into place at both gable ends, creating a finished product straight away.

A two-week programme had been allocated for the roof, but DTE completed the project, with the roof wind and watertight, in just five working days. “One of the benefits of using timber roof trusses is the speed of construction, and this project demonstrated how quick the erection process can be, even for a complex roof. We had the roof complete very quickly, which was, of course, a bonus for Bowmer & Kirkland, saving time and money.”

Mr Cook described the contract as a “brilliant project” that was interesting to work on, due in part to the challenging aspects of the job – the curved trusses and spandrels, the wide spans of the trusses and the fire break.

“But the beauty of timber trusses is that they can be precision engineered to meet very specific design needs,” he said. “The build went extremely well, and the roof looks fantastic.

“We don’t have any more curved roofs in the pipeline, but I look forward to the next design challenge.”