BSI has published the 2016 update of BS EN 350 Durability of wood and wood-based products: Testing and classification of the durability to biological agents of wood and wood-based materials. This important standard was last updated in 1994 and the new version incorporates a number of changes that will, for example, affect recommendations on using the heartwood of a species based on its inherent natural durability.

Scope of BS EN 350 expanded
The standard also rolls up the previous two parts of EN 350 into a single part combining durability classifications of species of economic importance in Europe with methods of assessing the durability of wood. The scope of the new standard has been widened to include wood-based panels, modified wood and preservative-treated wood as well as the natural durability of solid wood. It should be noted that the option for preservative treated wood is only possible in limited cases and for comparative use; the existing standards used for testing preservative-treated wood as described in EN 599-1 are still mandatory and the means by which efficacy of wood preservatives is assessed. The 1994 version only dealt with natural durability of solid wood.

In relation to the fungal performance of some species, two durability classifications are listed i.e. X (Y).  X is usually derived from the rating of heartwood stakes exposed outdoors in soil contact and in some cases combined with data from laboratory based, in soil contact soft rot tests. Y is determined from laboratory tests that assess performance against certain decay fungi.

The UK voted against the adoption of this new version principally because the laboratory methods for assessing durability in the new standard are, in the opinion of the UK committee, unsuitable for delivering a useful measure of durability. More detail on the UK’s position is included in the National Foreword to BS EN 350: 2016.

Important natural durability tables
The most important parts of the new standard are the tables describing the natural durability of the heartwood of species used commercially (expressed as class of durability against wood-destroying fungi, wood-boring beetles, termites and (where known) marine borers), the treatability of sapwood and heartwood and an indication of sapwood width. The classifications for 31 softwood species, 36 temperate hardwoods and 134 tropical hardwoods are given together with classifications for commercial groupings such as Hem/Fir.

The usefulness of the standard on its own is limited not least by the absence of any assessment of service life for a given durability classification. Wood durability is, furthermore, only one factor that influences the service life of wood, along with, for example, end use, climate and conditions of use, design and maintenance.

Consequences for other standards
Guidance on service life is dealt with for the UK in BS 8417 Preservation of wood – Code of practice which, while it focuses on service life for wood treated with preservatives, also provides a guide to service life of heartwood used in the five use classes (UC) that describe the in-service conditions experienced by wood – interior dry (UC1), interior with risk of wetting (UC2), exposed but not in ground contact (UC3), in contact with the ground or fresh water (UC4) and in the sea (UC5). The UK standards committee will now have to revisit BS 8417 with a view to considering the impact of the changes to BS EN 350 on UK practice when relying on natural durability for performance and service life as well as the inclusion of other wood-based materials.

TDCA will be updating its guidance to reflect the content of the new standard.  Worthy of note, are changes to the following:-