The TTF said that with different sizes being offered, concerns had been expressed that some products would not meet the relevant standard and may be used inappropriately.
Nick Boulton, the TTF’s head of technical and trade policy, said: “The structural performance is calculated using its strength grade and its exact dimensions.
“Any form of processing which removes wood from the cross-section will reduce the load that a piece can carry, or will reduce the span over which the same load can be carried.
“For this reason, members should be careful to ensure when advertising, or selling, strucutural timber that the exact dimensions are clearly stated.”
Mr Boulton said failure to provide this information could breach Trading Standards legislation or result in the joist being overloaded.
TTF members can obtain a copy of the advice note by emailing nboulton@ttf.co.uk.
