Timber Grading - further information
The grading of timber, essential in order to maintain consistency and to ensure reliability, can be defined simply as the sorting of wood sawn from a log into different qualities relating to classifications for appearance, end use or strength. Cladding and decking is classified as ‘constructional timber’ that is required to perform a secondary load-bearing function, and grades of which have clearly defined appearance qualities but which do not have any prescribed design values.
A timber grade is a minimum standard describing the extent and limitations of the characteristics permitted in a piece of timber having regard to the end use for which the grade is intended. Since no two pieces of timber are the same, some of the pieces that fall within the grade will have fewer of the permitted characteristics and will therefore be at the upper level of the grade. On other pieces more of the permitted characteristics will be present and therefore will be at the lower level of the grade. It is important to remember that complete uniformity of wood within either grades or shipments is impossible, so any shipment of a specific grade shall not be made up only of pieces containing either the minimum or maximum number of characteristics permitted.
It is also important to recognise both the difference between grades and the variability within grades especially when specifying to achieve an individual end result, particularly visually, and to note that the more the wood has to be sorted to exclude unwanted characteristics in order to achieve consistency in appearance (the higher grades) the more expensive will be the end product.
If a particular finished appearance is required, unless you are familiar with the nuances within and differences between commercial grades don’t rely on just commercial grade specification (e.g. No 2 Clear & Better) to achieve your end result, if possible visit suppliers to view the material and compare the actual specifications and appearance. Different mills and UK suppliers will have different interpretations of the grades. Some will push the lower boundaries of the grade to enable them to push a cheaper product onto the market; others will focus on quality and consistency.
If quotations based on the same specification for the same contract are considerably different, find out why, there will be a reason – don’t automatically go for, and don’t let your contractor go for, the cheapest! Get sight of the material (not just hand samples) – it may appear to be a bargain but it might also be of inferior quality and it may end up costing more overall due to the necessity to re-sort on site and cutting to remove unwanted characteristics.