C and D – what do they stand for?

The European Standard EN 338 contains a list of strength classes for structural timber.  There is a set primarily for softwoods which begin with the letter C (e.g. C16 and C24) and a set for hardwoods which begin with the letter D (e.g.D24 and D30).

It is sometimes said (e.g. 1, 2, 3) that the C stands for Coniferous and D stands for Deciduous.   This doesn’t really make sense.

Firstly – the 2016 revision of EN 338 allows hardwoods to be assigned to C grades…so they are no longer exclusively for softwood.  But there is a more fundamental issue…

Softwoods are conifers.  Conifers are gymnosperms – cone bearing seed plants.

Hardwoods (or broadleaves) are angiosperms – flowering plants.  More particularly, they are dicotyledons (they have two seed leaves) putting them in a different category from bamboo (which is a monocotyledon, one seed leaf)

Whereas…

Deciduous means that the tree loses its foliage for part of the year – as opposed to evergreen, where the foliage is kept all year.

Hardwood is not synonymous with deciduous.   Many tropical timbers are evergreen – so it would certainly not make sense to think that the D in D70 Greenheart stands for deciduous!

And while we are on the topic – conifer is not synonymous with evergreen either!  The most familiar deciduous conifers are larches – but there are a few others too (list below).

So what do C and D stand for?  Well – they don’t need to stand for anything.  But if they had to – Conifer and Dicot would make slightly more sense.

 

Deciduous conifers:

Larches, which include
Larix decidua (European larch) [LADC]
Larix kaempferi (Japanese larch) [LAKM]
Larix x eurolepis (Dunkeld larch) [LAER]
Larix occidentalis (Western larch) [LAOC]
Larix gmelinii (“Siberian” / Dahurian larch) [LAGM]

Pseudolarix amabilis (Golden Larch)

Taxodium distichum (Southern / Bald cypress) [TADS]
Taxodium ascendens (Pond cypress)

Glyptostrobus pensilis (Chinese Swamp Cypress)

Metasequoia glyptostroboides (Dawn Redwood)

[XXXX] is the EN 13556 species code

 

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