PLGN 5.04 Durability of Heartwoods

Wood is an extremely useful building material. However the nature of timber demands that the species, the protective coating systems and the conditions of service are chosen carefully to ensure success. Being a natural material wood is susceptible to attack from:

  1. Moisture uptake leading to dimensional movement.
  2. Fungal attack - from destructive wet and dry rots to disfiguring surface moulds normally when moisture content exceeds 20%.
  3. Breakdown of the composition of wood by sunlight (ultra violet and visible light).

The basic types of wood fall into three categories - Hardwood, Softwood and Resinous Softwood with a further Subdivision of each for Heartwood and *Sapwood.

Generally hardwoods are more durable and dimensionally stable than softwoods with sapwood the least durable in all three types. When choosing the type of wood for any particular application its cost, conditions of service and appearance must be considered.

Very Durable - more than 25 years: Hardwoods

Afrormosia, Afzelia, Guarea, Greenheart, Iroko, Iron bark, Jarrah, Makoré, Muninga, Opepe, Purpleheart, Pyinkado, Teak, Turpentine.

Durable - 15-25 years: Hardwoods

Agba, Chestnut, Sweet Idigbo, Mahogany, American Meranti, Red Muhimbi Oak, European Utile

Durable - 15-25 years: Softwoods

**Western Red Cedar, Yew, Sequoia (Californian Redwood)

Moderately durable 10-15 years : Hardwoods

African Walnut, Avodiré, Ayan, Dahoma, Guriun, Indian Keruing, Malayan Mahogany, African Oak, Turkey Sapele, Walnut European.

Moderately durable 10-15 years : Softwoods

Douglas Fir, Larch, European and Japanese Pine, Caribbean Pitch Pine, Maritime Sequoia (home grown), Western Red Cedar (home grown)

Non-durable 5-10 years: Hardwoods

Elm, Dutch Elm, English Elm, Wych, Oak, American Red Obeche, 'Silver Beech' Seraya, White Sterculia, Yellow.

Non-durable 5-10 years: Softwoods

Douglas Fir (home grown)Fir, Balsam Fir, Grand (home grown) Fir, Silver (home grown) Hemlock, Western Parana Pine, Pine, Scots (home grown) Redwood (imported), Spruce, Eastern Canadian Spruce, European Spruce, Sitka (home grown), Whitewood.

*All sapwood is either non-durable or perishable

**Cedar - The most commonly used form of cedar for building purposes is Western Red Cedar also known as British Columbia Red Cedar. It is grown in Europe and North America. Western Red Cedar is a reddish-brown non-resinous lightweight Softwood with straight grain and prominent growth rings. It is very durable and often used for vertical cladding garden buildings greenhouses etc. Cedar contains oil which may impair drying, hardening or adhesion of surface coatings. Staining or corrosion of iron and steel fittings etc. can also be a problem due to the acidic nature of the wood (see BS 6150:1991 25.1.4 Extractives for further Information). Staining may also occur if water-based paints are applied. Cedar is a strongly scented wood with a resinous heartwood.