Visual strength grading of timber is carried out according to grading rules that are usually (but do not have to be) national standards (like BS4978 for softwoods and BS5756 for temperate hardwoods). How these visual grades correspond to strength classes (assignment to a strength class) is specific to a combination of grading standard, species and timber source. EN1912 is the European Standard that lists assignments for visual grades of structural timber to strength classes. It is due for a revision. What follows is some background information and summary. Scroll to the bottom for more detailed information.
(EN1912 does not list all the assignments for visual grades to strength classes. Assignments may also be listed in other standards or documents as long as they do not contradict EN1912. EN1912 is also limited in scope to only the strength classes that are listed in EN338 – but using those strength classes is not always the best option – and there are several strength classes that don’t appear in EN1912, including a very common in the UK market, TR26.)
EN1912 only lists assignments of visual grades to strength classes that are based on one of two things:
- Testing and calculation – written up into reports that have been approved by CEN TC124 WG2 TG1 (“TG1”) (the current standard for this is EN384, but old assignments may have been done to other standards)
- Or have been listed on the basis of common and long-standing practice. This really only applies to old assignments – added into EN1912 when it was still a new standard – since this is not considered a strong evidence basis these days.
The visual grading assignments for UK grown timber are all relatively old, and not all of them are listed in EN1912. The following are included:
- British spruce (Sitka and Norway spruce)
- British pine (Scots and nigra … see below)
- larch (European, Japanese and hybrid)
The visual grading assignments for large cross-section Douglas-fir, oak and sweet chestnut are instead in PD6693 a published document from BSI.
EN1912 does include multiple assignments for timber grown elsewhere, that has been graded to the British Standards. Since there is now a European Standard for visual grading of tropical timber (EN16737) that replaces the rules for tropical timber previously in BS5756 these are among the assignments that need to be updated in EN1912.
EN1912 needs updating for the following reasons:
- To improve the text and make it compatible with changes to other standards (notably EN14081-1)
- To add in new visual grading assignments that were approved by TG1 since this version of EN1912 was written (and some approved before then, but were not included by mistake)
- To update references to the visual grading standards
- To clarify (and better define) both species and growth areas
- To include some information about how the assignment got into EN1912
- To make some changes to how the information is tabulated to make the standard easier to use
In order to do this, CEN TC124 WG2 (“WG2”) will be writing to mirror committees of the National Standards Bodies requesting an answer to three questions before April 2020.
- To clarify the growth areas (timber source), where this is currently too vague.
- To give information about the evidence base for the assignment, where this is not already known by WG2
- To give up to date information about the grading standards – specifically the bibliographic details and whether there have been any changes to the standards that might affect the grading
If vague growth areas are not clarified, the anticipated course of action is either to remove the assignment from EN1912, or to restrict to the country publishing the grading standard (if this makes sense).
If no information is provided about the evidence base of an assignment, the anticipated course of action is that this assignment will still be listed, but will have some kind of indication that marks it as different from assignments where the evidence base is known.
There is some more detailed information about these topics, and other corrections below.
The timetable for revision of EN1912 is expected to be:
29/02/2020 : Deadline* for new visual grading reports to be sent to TG1
31/03/2020 : Deadline for comments from mirror committees
30/04/2020 : Comments digested by TG1 and sent to WG2
07/04/2020 : The first day of a two day meeting of TG1
26/05/2020 : The first day of a two day meeting of WG2 to discuss the update
31/05/2020 : An updated draft of EN1912 is produced and the formal CEN process of revising EN1912 is requested
30/06/2020 : WG2 members feedback comments on the draft
31/07/2020 : Expected date by which the formal CEN process of revising EN1912 begins
01/10/2020 : Expected date at which the draft of EN1912 will go to public comment (“Enquiry”) – a process that takes one and a half months.
* reports may be accepted after this date, and before the TG1 meeting, but it is not guaranteed that TG1 will have time to review them. Visual grading reports may be approved at later meetings – if they do not get approved in time for the EN1912 update they will get listed in an “AGR” produced by TG1 and circulated to Notified Bodies via SG18 (the process already in place for assignments pending EN1912 inclusion).
Aside from the formal process, and the responses to the letter from WG2 to the national mirror committees, you can also contribute to the update of EN1912 by contacting Dan Ridley-Ellis, who maintains a database of the visual grading assignments and metadata. You can read more details of changes below.
There are many new visual grading assignments to be included in EN1912. Some of these were covered by recent AGRs produced by TG1, but many are older and were only documented in meeting minutes and the TG1 report archive. A detailed check of this has been done, but things may still have been missed so it is advised to check any new draft of EN1912 for assignments you expect to see in there. If they are missing (or different from what you expect) this might be by mistake. Pending assignments which have been approved on reports submitted to TG1 are now listed in a single consolidated AGR. At time of writing this has been circulated via WG2 and has the reference “AGR-VISUAL-2019-11-07”. Contact Dan Ridley-Ellis if you have any comments.
There was an Irish request to WG2 that assignments under BS4978 also be adopted for IS127 based on equivalence of the grading rules. This would apply also to the grading of imported timber, but certainly it makes sense to consolidate the growth area for spruce, which we know to be the same in UK and Ireland – allowing grading of UK grown spruce to the Irish Standard and Irish grown spruce to the UK standard.
Since tension classes are now included in EN338 it would also be possible to include assignment from a 2007 report that assigned spruce and fir from Germany, Austria and the Czech Republic to tension a tension class. This assignment is also unusual as it combines visual grading with a density measurement made directly by mass (a machine referred to as “VM-Grader”, but treated under the system of visual grading).
Tropical timber assignments previously under BS5756 will be converted over to the new EN16737 (the rules produce the same grading). Assignments to the Dutch standard NEN5493 are in the same position but will also be retained in EN1912 in their own right due to NEN5493 having some additional requirements relevant to use in the Netherlands.
More specific growth areas
Several of the current visual grading assignments are defined by too large or ambiguous growth areas. These should be better defined in the new standard as growth area is very important for timber properties (and how they relate to the grading parameters). This is ever more important now that the timber trade is more international and timber is coming from places it was not before.
The growth areas most in need of clarification are:
- For grading under British standards (and to become EN16737 for the tropical timber)
- “Africa” for iroko
- “Caribbean” for Caribbean pitch pine
- “Central west Africa” for sapele
- “Central, Northern and Eastern Europe (CNE)” for Norway spruce, Scots pine/redwood and whitewood
- “South East Asia” for balau/bangkirai, kapur, kempas, keruing, merbau and teak
- “West Africa” for opepe/bilinga
- For grading under Austrian, Czech, Slovak and German standards
- “Central, Northern and Eastern Europe (CNE)” for larch, Norway spruce, Scots pine/redwood and silver fir
- For grading under the Nordic Standards
- “Northern and North Eastern Europe (NNE)” for larch, Norway spruce and Scots pine/redwood and Silver fir
- For grading under Dutch (Netherlands) standards
- “Northern and North Eastern Europe (NNE)” for larch, Norway spruce and Scots pine/redwood and Silver fir
- “West Africa” for ekki/azobé
- For grading under the French standards
- “South America” for ipé/ebene verte
The growth area “Northern and Central Europe (NC)” is mentioned in the text of EN1912 but it has no assignments.
Some of these are more ambiguous than others – but even ones that describe an area that has a generally agreed geographical or political definition the actual growth area it should be may not match that. A better method is by direct reference to countries or parts of countries (but even that is not entirely straightforward for the pedantic).
Updated species information
Species is something that is also potentially ambiguous (as can be seen in the list above … e.g. for larch), even when using botanical names (not everything is settled). Currently EN1912 uses index numbers, reference to EN13556, and (incomplete) botanical names. The problems with this include that EN13556 is not just for structural timber (or under CEN TC124 WG2) and so it is not a complete, stable, or necessarily correct standard to use for defining species for grading (although it is useful for marking timber after grading). Updates and improvements need to be made to both the specification by botanical names, and the use of common names and trade names (both for species and groups of species).
As well as stating taxonomic authorities for all the names, these include:
- Beilschmiedia spp. Nees, 1831 which is misspelled in EN13556
- Chlorocardium rodiei (R.H. Schomb.) Rohwer, H.G.Richt. & van der Werff, which appears in EN1912 as Ocotea rodiaei even though EN13556 lists Chlorocardium. (Probably EN1912 should list both names as synonyms)
- Dicorynia paraensis Benth. which maybe should be included with Dicorynia guianensis Amshoff (or the meaning of basralocus/angelique clarified in EN1912)
- Fraxinus americana L., which is included with F. nigra and F. pennsylvanica in EN13556 and perhaps should also be for EN1912
- Gambeya spp., which is now more accepted as Chrysophyllum spp. L. (this is down to the conventions of taxonomy – probably EN1912 should list both names as synonyms)
- Larix decidua Mill. which is misspelled in EN1912
- Larix × eurolepis A. Henry which is now more accepted as Larix × marschlinsii Coaz (this is down to the conventions of taxonomy – probably EN1912 should list both names as synonyms)
- Manilkara bidentata (A.DC.) A.Chev. which is misspelled in EN1912
- Newtonia suaveolens Brenan, which is now more accepted as Pseudopiptadenia suaveolens (Miq.) J.W.Grimes (probably EN1912 should list both names as synonyms). Pseudopiptadenia psilostachya (DC.) G.P.Lewis & M.P.Lima. should also perhaps be included in Alimiao
- Picea engelmannii Parry ex Engelm. which is misspelled in EN1912
- Pinus nigra J.F.Arnold which needs to be more specific in assignments (especially as the common names are very confusing – as are some of the botanical synonyms!)
- Pinus nigra subsp. nigra (Austrian pine)
- Pinus nigra subsp. laricio Maire (Corsican pine)
- Pinus nigra subsp. Salzmannii (Dunal) Franco 1943
- Populus × euramericana, which is now more accepted as Populus × canadensis Moench, 1785 (this is down to the conventions of taxonomy – probably EN1912 should list both names as synonyms)
- Ruizterania spp. Marc.-Berti is not included with Qualea spp. in the EN13556 listing for mandio/gronfolo
- Tabebuia spp. which is now more accepted as Handroanthus spp. Mattos, 1970 (probably EN1912 should list both names as synonyms)
- Quercus alba L. which is listed in EN13556 less specifically (under American white oak), and possibly EN1912 should also be less specific
- Quercus rubra L. which is listed in EN13556 less specifically (under American red oak), and possibly EN1912 should also be less specific
- Shorea glauca King and Shorea maxwelliana (King) Symington, 1938, which is listed in EN13556 less specifically, and possibly EN1912 should also be less specific (or EN13556 more specific)
There are also several species that are not currently listed in EN13556 but are used for visual grading assignments (or appear in EN14081-1 species combinations):
- Abies concolor (Gordon & Glend.) Lindl. ex Hildebr., 1861 (is in hem-fir WABA)
- Abies magnifica A.Murray bis (is in hem-fir WABA)
- Desbordesia glaucescens Van Tiegh. (alep/banga/omang)
- Klainedoxa gabonensis Pierre (eveuss/eves/kuma-kuma/ngon)
- Manilkara mabokeensis Aubrev. (monghinza/adzacon-aboga)
- Picea mariana (Mill.) Britton, Sterns & Poggenb. (appears in S-P-F WPCE)
- Picea rubens Sarg. (appears in S-P-F WPCE)
- Pinus nigra subsp. Salzmannii (Dunal) Franco 1943 (Salzmann pine)
- Pteleopsis hylodendron Mildbr. (osanga/koframiré)
- Ruizterania spp. Marc.-Berti (mandio/gronfolo) (only Qualea spp. is listed)
- Scyphocephalium mannii Warb. (ossoko/sorro)
- Tsuga mertensiana (Bong.) Carriere (appears in western white woods WABB)
Contact Dan Ridley-Ellis if you have any comments.