Photo credit: Vida Wood
A new technical card has been issued by the TRA to discuss the use of alternative timber grades during the softwood supply shortage.
The card describes how TR26 grade became the predominant requirement for the trussed rafter sector in the UK. Timber suppliers have specialised in this grade as it’s economically viable due to its high demand. This means the sector benefits from a TR26 price per cubic metre which tracks only marginally above the standard C24 grade price per cubic metre in the UK market.
There are no technical barriers to prevent TRA members using alternative standard strength classes as system design software allows the intended raw material strength class to be set as a parameter of the design.
Nick Boulton, chief executive of the TRA, says there are safety considerations if using other grades: “Metal web joists, for example, require square edge raw material, as a greater proportion of teeth fixings are close to the edge, making this zone critical for safety. Trussed rafter designs could potentially allow some degree of eased edged material such as C24, but the size of radius is critical to the correction measures necessary, which may include increased edge distances and larger truss plates. Fabricators must always contact their system provider to discuss correction measures before using eased edge raw materials.”
In the absence of sufficient TR26, could the standard of C24 timber be an alternative? Many fabricators have looked at the economics of doing so. However, very few have made the decision to switch even part of their production. This suggests that even in the present market conditions TR26 and standard ‘trussed rafter parameters’ still represent the most cost-effective solution for TRA members.
Read about the properties of TR26 here