The requirement for timber durability depends largely on the use class in which the timber is being used. Subject to the natural durability of the timber species and the use class preservative treatment may be advisable.
I.S. 440 “Timber Frame Construction, Dwellings and other Buildings” specifies preservative treatment for a number of timber components including studding, top and bottom rail and sole plates. Otherwise it is generally up to the building designer to specify treatment in the works specification.
Most preservative treatments of timber used in buildings in Ireland have been tested to EN 599-1 “Durability of wood and wood-based products – Performance of preservatives as determined by biological tests – Part 1: Specification according to hazard class”.
The Wood Protection Association (WPA) represents the treatment industry and its manual on wood preservation has been a valuable source of information on treatment for a considerable period of time. BS 8417:2011 “Preservation of wood - Code of practice” is also reference document and provides similar information as the WPA manual; the information being essentially the same. BS 8417 has also been in existence and has been used in Ireland for some time.
The definition of use class is given in EN 335 “Durability of wood and wood-based products - Use classes: definitions, application to solid wood and wood-based products”. However BS 8417 further sub-divides these use classes based on service factors (including cost of replacement) and gives good guidance on the need for timber preservation.
EN 15228 “Structural timber – Structural timber preservative treated against biological attack” requires the timber treater to supply information on the treatment method, the preservative, the specification complying with national provisions, the penetration class, the retention value including the units, the charge number and year of treatment, the target biological agents and the identification of the treater. This information can be requested by the timber purchaser, building designer (or assigned certifier) or building owner.
More information is given in our Timber Information Sheets.