Strength Grading
What is strength grading?
BSW produce strength graded timber to specifications laid down in British Standards - BS4978 for visual grading and BS EN 14081 for machine grading. Timber is graded to strength classes. The most commonly specified grade for softwood carcassing is C16.
What are the benefits of strength grading?
Strength grading is undertaken primarily to provide timber of sufficient strength for a particular function, e.g. a floor joist or a roof truss. At the same time strength grading helps to ensure that both the design and the timber sizes specified are economical. How do BSW strength grade?
After kiln drying to an average moisture content of below 20%, the timber is passed through a highly automated grading line where a combination of measurements are taken which closely relate to strength. From this, the machine determines the Strength Class of the piece of timber. The machines are calibrated daily and the company operates a third party certification scheme under ISO 9000.
To satisfy British Standard building regulations, structural timber used in buildings must be kiln dried to an average of approximately 20% or less and be marked DRY or KD. The grade stamp must also contain information on the species - the strength class - the graders licence number - the BS number and the certification body logo or mark.
