Table A 12.1 has been scored on the basis of natural durability, timber density, moisture movement and end use suitability. Most timbers will score in the region of 4 to 5 for exterior use if they are given the recommended preservative treatment in accordance with their likely exposure or hazard class, for example, Hazard Class 3A for external joinery and cladding. Some species such as iroko, mahogany, white oak and teak are extremely resistant to preservative impregnation treatment but their natural durability more than compensates.
Western red cedar would be as naturally durable as white oak but its low density and softness make it unsuitable for areas where strength or abrasion resistance is required, such as glazed doors, opening windows or thresholds. Non-durable species listed at "1" in the table below - Ash; beech; maple and sycamore are unsuitable for exterior use.
Both oak and western red cedar are acidic and will corrode most metals and cause rust staining in damp conditions. Choose stainless steel fixings in these conditions. Silicon bronze or stainless steel ringshank nails should be used for all external cladding. Galvanised or aluminium nails will stain cladding within a short time. Stainless steel pins are best for joinery. Aspects such as colour and texture have not been included in the table and samples should be sought prior to final specification.
Table A 12.1 Joinery species suitability (71Kb)