Machine Strength Grading is the process whereby machines are used to determine strength classes and has prompted the development of a range of devices using differing technologies to determine the strength of timber. The common factor with all these machines is their ability to measure a number of properties of a piece of timber and relate these measurements, through rigorous testing programmes, to predict the strength properties of the piece and assign the appropriate Strength Class.
The Standard for controlling machine Strength Grading operations within UK/ Europe, which is also now being adopted in other countries, is EN 14081-1-4. This Standard is supported by EN 338 which provides the Characteristic Values (used by structural engineers) of strength to the Classes C14-C50 for softwoods.
Recognised grade marking on a piece of timber is its “Passport” for use in Structural applications and assures acceptability ay authorities such as Building Regulation, Building Control, NHBC etc. These Standards require that graded material is supplied and marked under the control of a recognised Scheme operated by a Certification/Notified Body such as Exova BMTRADA. Production and marking by the machine grading process requires successfully passing an initial and subsequent twice yearly inspection of production control by a body such as Exova BM TRADA.
Exova BM TRADA has been providing strength grading certification to the timber and construction industry since the early 1970s under the Exova BM TRADA Q-Mark brand and more recently including CE marking.