Machine strength grading of structural timber in Europe is done mostly under a system called “machine control”. The machine settings are fixed based on large destructive testing programs, and sawmills can run these settings as long as they have the right combination of machine, species and timber source. In recent years there has been much development of new grading machines, extending growth areas and developing settings for additional species. In a new journal paper, Dan Ridley-Ellis, David Gil-Moreno and Annette Harte present the current strength grading options for timber grown in the UK and Ireland. Most of this is based on research done by Edinburgh Napier University and the National University of Ireland, Galway. This is the only comprehensive list of information that is, otherwise, difficult to obtain. The paper is open access, so anyone can read it on the journal’s website:
Dan Ridley-Ellis, David Gil-Moreno & Annette M. Harte (2022) Strength grading of timber in the UK and Ireland in 2021, International Wood Products Journal, Vol 13, No 2, p 127 – 136,
Please note that the journal’s formatting currently doesn’t work well for the web version, so it is best to look at the pdf version.
Abstract: “This paper summarises the state of the art for strength grading of construction timber grown in the United Kingdom and the Republic of Ireland. It includes the latest approvals based on recent research on spruce, larch and Douglas-fir. It lists the following information along with the primary references: visual grading grades and strength class assignments; grading machines with approved settings for machine control grading; the species, size ranges and strength class combinations covered; and grade determining properties of specific strength classes for the UK and Irish markets. This paper is useful for those grading timber, and those specifying UK and Irish grown timber.”
The paper includes:
Species combinations (and codes);
Definitions of special (“user defined”) grades such as TR26 and C16+;
Properties of UK and Irish grown spruce, larch, Douglas-fir and pine;
A list of grading machines approved for machine control grading*;
A comprehensive list of machine grading possibilities and the confidential reports on which they are based;
Visual grading assignments to IS127, BS4978, BS5756 (via EN1912 and PD6693-1) including also oak and sweet chestnut.
* The machines include Microtec Goldeneye 702 x-ray grading machine and the Brookhuis MTG handheld acoustic grading machine, as well as the bending machines like the Cook Bolinders.
For an explanation of the grading framework (under EN14081) see
Ridley-Ellis, D., Stapel, P. & Baño, V. Strength grading of sawn timber in Europe: an explanation for engineers and researchers. Eur. J. Wood Prod. 74, 291–306 (2016). https://doi.org/10.1007/s00107-016-1034-1