To the uninitiated, the visual grading and appearance grading of timber are the same thing, but this would be to confuse two quite separate assessment methods. Essentially, grades for timber are divided into two categories – structural and non-structural, and visual grading is one of the methods used to assess the load-bearing characteristics of timber. Appearance grading, meanwhile, is a means of assessing timbers for non-structural purposes such as flooring, furniture, or external cladding.
Until recently UK-grown hardwood timber lacked a reliable standard for appearance grading. This might seem a small issue, since many UK sawmills and timber merchants already use an appearance grading system of some kind, but for architects, furniture makers, and other end users the very existence of different approaches has meant doubts that material being supplied would actually match the characteristics specified. The first serious move away from this uncertainty began in 1996 when European Standard EN 975-1 introduced appearance grades for oak and beech. To date, however, take-up has been limited. Its presentation is complex and arguments have also been made that the grades do not suit UK timber and that commercially important species such as ash and sycamore are not included.
In response to these issues, Making the Grade – a guide to appearance grading UK grown hardwood timber by CTE research fellow Ivor Davies and Guy Watt of John Clegg Consulting Ltd, was recently published to provide a national commentary on EN 975-1 and to extend coverage to the other hardwoods commonly available in the UK. As far as possible, the new document follows the grading criteria in EN 975-1 and, in most respects, the grades it gives are interchangeable with those in the standard. Even though it has been necessary to make changes to accommodate the timber availability, species, characteristics, and production methods found in the UK, the grading system has been made as simple and logical as possible. The guide covers: ash, beech, oak, sycamore, sweet chestnut, cherry, lime, and elm, and applies to both square- and waney-edged timber. The grades are primarily determined by the size and frequency of knots and splits on the best face of the timber.
In each instance three grades are given. Equivalent to what is often called ‘clear’ or ‘prime’, Grade 1 describes timber having a uniform appearance with few knots, splits or other features that would limit use in applications where little variation in appearance is permitted. Grade 2 has some knots or other features that limit use where uniformity of appearance is important but the piece will yield areas clear of unacceptable features along with timber suitable for applications where some variation is acceptable. Grade 3 timber includes all manner of knots, splits, colour variation and other features.
The guide sets out these criteria in easily referenced tables with extensive notes and a glossary. The timber species are shown in detail and care has been taken to allow accurate colour and scale comparisons to be made. Appendices cover everything from the measurement of sawn hardwood timber to criteria for specification, sourcing and certification.
To complement the publication, a CD-ROM is available. This contains all of the same material and has been designed for use on any computer with Adobe Acrobat. The CD-ROM’s simplified structure allows the information to be accessed by even the least computer literate person. Available free, Making the Grade cannot help but succeed in the stated aim of encouraging greater use of UK-grown hardwoods. y
l Making the Grade is available free from: Forestry Commission Publications, PO Box 25, Wetherby,
West Yorkshire, LS23 7EW; tel: 0870 121 4180;
e-mail: forestry@twoten.press.net.
