FEATURES
On the right side of the
timber treatment law
According to the South African Preservation Association (SAWPA),
wood preservation is the treatment of wood to increase durability and
extend service life to non-durable timbers. Specific laws are in place to
preserve timber in South Africa, especially timber used in construction.
By Dineo Phoshoko | Images by SAWPA
TIMBER AS A STRUCTURAL MATERIAL
For centuries, timber has been used as a building material.
The Structural Timber Association (STA) notes that with
time, developments in various types of timber components
and their use in different structural forms have occurred.
Such developments have made it possible for new
advanced timber products to be available – allowing
structural engineers to achieve the performance and
efficiency in building forms demanded in the 21st century.
In her article titled ‘Introduction to timber as an
engineering material’, Dr Annette M Harte from the
Institution of Civil Engineers ICE journal (UK) mentioned
that timber remains an important construction material
thanks to research and improved technology that has
improved the knowledge of the material’s behaviour. “This
has helped designers to use timber more efficiently and
safely and in more challenging and exciting applications,”
she wrote.
Using timber for structures did not happen by chance as
there are many benefits to using timber as a building
material. According to the STA, Timber is a renewable
resource and therefore has impressive ecological
attributes; it acts as a carbon sink and has low embodied
energy. In comparison to the energy required for other
building material such as steel and concrete, the energy
needed to convert wood into structural timber is far less.
Another reason that makes timber a desirable choice for
construction is that it is strong and has a high strength-to-
weight ratio. Timber material is also easy shaped and
modified and waste material can be recycled. Timber does
not require complex building materials as it can be easily
connected using nails, screws, dowels, bolts and
connectors. Under controlled conditions of temperature
and humidity, adhesives may be used to glue timber
elements together. Another reason highlighted by the STA
is that timber and its components are lightweight and easy
to handle in terms of manufacturing, transport and
construction. A building structure with a timber finish is
also aesthetically pleasing.
36 APRIL / MAY 2019 //
MARKINGS FOR CORRECTLY TREATED TIMBER
ABC TT: MANUFACTURER ID
Q-MARK: QUALITY MARK OF APPROVAL, E.G. SABS or SATAS
457: SANS NATIONAL STANDARD NUMBER
18: YEAR THE POLE WAS PRODUCED
H4: CODE FOR CHEMICAL TREATMENT LEVEL & END USE
BASIC AND PHYSICAL PROPERTIES OF TIMBER
Timber is complex and has various properties that if not
treated, will have a negative impact on its durability, which
will affect the structures in which it is used.
‘Because it is a naturally grown material, timber is a
complex building material. Its properties are highly variable
and are sensitive to environmental and loading conditions,’
Harte writes. She mentions that it is important to take such
factors into account when considering the design of
timber structures.
Poles Galore manager Joe de Klerk adds that the natural
properties differ from tree to tree making selection of timber
an important process. Moisture is a basic property of timber.
Harte explains moisture as a hygroscopic material because it
exchanges moisture with its surroundings and its properties
vary significantly with moisture content.
See more on page 38
www.timberiq.co.za