Long life part of the TRA legacy

Neil Summers of the Trussed Rafter Association explains the resilience and sustainability credentials of timber trussed rafters.

With whole life costs, issues of sustainability and the increasing incidence of PFI projects, component life credentials are necessarily determining a great number of specifications.

If we consider the roof as the element of the building envelope which shoulders the greatest responsibility for protecting the rest of the structure, most covering materials such as concrete tiles carry warranties extending from 25 years, onwards to half a century.

Such security would not, however, be of much value if the roof structure itself were it not to endure for a similar period or longer.

It is an issue which members of the Trussed Rafter Association take fully into consideration, not only in their design calculations, but also their quality control and the nature of the protection afforded to the finished trusses.

Timber's excellent strength-to-weight ratio and good insulating properties make it an outstanding material for supporting a roof.

Expertly engineered roof truss structures give very good loadbearing capabilities.

They may be sized to support everything from small scale domestic dwellings to large, long span industrial buildings.

Timber is, in addition, our only natural renewable resource and requires lower energy usage to process than other constructional materials.

Moreover, manufacturers can offer specifiers products fabricated from softwoods harvested from fast grown, well managed sites including stocks that are certified as coming from a sustainable source.

Despite the slenderness of sections seen, and the use of adhesives or nail plates where once hand cut joints and hardwood dowels would have been the preferred method of assembling roof trusses, building owners can expect the modern trussed rafter to offer a service life equivalent to, or greater than, its far heavier predecessors.

An important part of this very healthy picture for the specifier is the availability of pressure impregnated timber or the use of similarly beneficial factory treatment processes; offered as standard or as an option by all members of the TRA.

Preservation treatment is an unseen benefit that the specifier or property developer can build in to the roof structure at minimal initial cost.

Factory preservation can be viewed as adding value and ensuring all elements in a roof structure are protected - something which would be impossible to be sure about if spraying was carried out once the roof is complete and the insulation is in place.

In certain areas of the country, where an insect known as the House Longhorn Beetle thrives, Building Regulations already direct the mandatory use of factory-applied preservatives for all construction timbers, while the Trussed Rafter Association strongly recommends that these regulations are adhered to.

During the last few years, there has been a need for manufacturers and treaters of roof trusses to move away from the more traditional solvent-based preservatives towards the water-based options.

This trend has been environmentally led from the point of view of a better working environment at the treatment plant and also because the water based materials represent a more user friendly material for the manufacturer.

For further information on the Trussed Rafter Association, please call Susan Farrow on 01246 230 036, or visit the website.

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