A construction material provided and renewable by nature, with predictable performance, that captures carbon from the atmosphere and locks it away for decades, with low energy demand and a feel-good appeal appreciated by almost everyone – that’s treated wood.
Wood is part of the bioeconomy, can be sourced responsibly, is a flexible and adaptable material that can be used efficiently and aligns with the concept of a circular economy. At the end of its life, wood can be reused in an ongoing process of uses, recycling or recovery of energy. Wood is consequently one of the few truly renewable construction materials.
Wood offers a simple way to reduce the CO₂ emissions through:
- the carbon sink effect of forests;
- the carbon storage effect of wood products; and
- substitution for carbon-intensive materials.
Not only is the production and processing of wood energy efficient, giving wood products a low carbon footprint, but wood can often be used to substitute other materials like steel, aluminium, concrete, or plastics, which require large amounts of energy to produce.
Every cubic metre of wood used as a substitute for other building materials reduces CO₂ emissions to the atmosphere by an average of 1.1 tonnes (t). If this is added to the 0.9t of CO₂ stored in wood, each cubic metre of wood saves a total of 2.0t of CO₂. Based on this, an increase in buildings whose main structural components are made of wood, will produce significant CO₂ savings as prescribed by the Kyoto Protocol*.
The natural durability of wood is limited to the heartwood, but this depends on the species, growth conditions and provenance. Apart from a very few, mostly tropical hardwood species, most untreated wood is vulnerable to biodeterioration by fungal decay and wood destroying insects.
These biological agencies also degrade the sustainability credentials of untreated wood leading to early failure in service, premature release of CO₂ and economic loss, more characteristic of a linear economy than a desirable circular economy.
Commercially important wood species are typically derived from locally grown well-managed forests delivering high growth rate material. Due to high demand, modern processing practices are designed to maximise wood production yield, meaning it is impractical and uneconomic to exclude sapwood.
The sapwood of all species is susceptible to insect and fungal attack, and requires protection against insect attack and, in prolonged wet conditions, fungal attack.
If non-durable, heartwood may also require protection depending on the wood species, the conditions of use and the service life required. Most South African grown commercially important species of pine and eucalyptus are non-durable and require preservative pre-treatment.
In recognising the short life of untreated wood when used in exposed applications and conditions, for example, agriculture, marine and freshwater areas, structures and fencing, and the inconvenience and cost of failure, humankind has from antiquity attempted to prolong the life of wood.
The discovery of the biological causes of wood damage and decay, coinciding with the start of the Industrial Revolution, led to the development of effective treatments.
This has culminated in the preservatives and processes available now for many uses of treated wood that meet the health, safety and environmental requirements of today’s regulatory regime.
For the full article read the August/September issue of Timber iQ.