Summary
• The commercial build sector is comparatively buoyant.
• DTE has contracts for care homes, hospitals and schools.
• The community hospital in Ayrshire required 48 different truss types.

While trussed rafter manufacturers are feeling the impact of the downturn in the newbuild housing market, they are finding some respite in the commercial sector.

“There’s definitely been a drop in our turnover,” said Mike Donaldson, general manager of Donaldson Timber Engineering’s (DTE) Buckhaven site, “but you notice it much more in newbuild. The commercial sector is more buoyant and there are quite a lot of care homes, hospitals and schools.

“We are certainly noticing some large projects coming our way. Some of these are up to £50-70,000 and anything of that scale at the moment is more than welcome.”

One such project is in Ayrshire, where DTE is supplying 4,694m² of trusses for the six wings of a new community hospital.

The largest of the wings – 1,472m² of trusses – has also proved to be the most demanding. “This block was particularly tricky as we had to house a first floor plantroom along the length of the building,” said Mr Donaldson. “We did this by forming a split level floor with a void zone in the centre floor using our joist system below the trusses.”

Truss types

This one block consisted of 359 individual trusses and 48 different truss types. The higher than usual number of truss types was required so the roof could accommodate the plantroom, walkways, two bridges and 40 skylights framed down to the ground floor corridors.

The main shape was formed using external mono type trusses to both planes and duo pitch top hat trusses along the main ridge line supported off the mono trusses below.

The eaves were to be exposed as a design feature so DTE supplied them pre-cut and shaped, ready for bolting to the mono pitch trusses on site.

“The spans were so large we had to make the trusses in three pieces and design and manufacture then accurately so they went together perfectly on site,” said Mr Donaldson.

The trusses for the one wing were delivered over two days in six full loads.

Because the eaves are exposed, the members had to be supplied without any grading or company stamps – a small thing, but working closely with the client and getting all the informtion right from the start means the small things are not forgotten.

“It’s these small things that can be overlooked, and if you do overlook it at an early stage, it becomes a real problem later on,” said Mr Donaldson.

Design team

He is full of praise for how DTE’s “fantastic team of designers” dealt with the complexity of the project. “Someone had to design 48 different truss types and make sure each one is absolutely spot on over the size of the hospital,” he said.

As DTE becomes more involved in larger projects it is finding that truss configurations are becoming more complex as roofs need to house services and architects push the boundaries.

“Trusses have been around for a long time but people are starting to ask more of them, using them in slightly different circumstances and getting some quite impressive spans,” said Mr Donaldson.

Architects could sometimes come up with some “pretty wacky ideas” but it came down to working with them to provide a solution. “It’s about trying to help these architects; work alongside them to allow them to get as close as possible to their desired outcome,” said Mr Donaldson.

DTE also has a couple of other large projects on the go – a care home with a floor area of 2,295m² and a hospital with 2,434m² of floor area.

These are all large projects but, as Buckhaven is Donaldson’s largest truss manufacturing site, with a capacity of 5,000 trusses a week, it is used to dealing with orders of this scale.

“It’s a lot of trusses for one job but it’s a case of production planning,” said Mr Donaldson.