Timber iQ February - March 2019 // Issue: 42 | Page 50

WOOD WISE
process, it takes up carbon dioxide from the atmosphere,
stores the carbon molecule (which it uses for energy) and
releases oxygen in a process commonly known as
photosynthesis. In addition, since wood is grown and is not
a finite resource, like oil, timber remains the only truly
renewable building material available.
South African pine, predominantly used in timber frame
construction in South Africa, has the propensity to take up
and store between 600kg to one ton of carbon from the
atmosphere per cubic metre of wood. Timber is arguably
the only building material that starts out having removed
carbon from the atmosphere before its working life, which
means it has a head start on mitigating the activities that
will later make up its embodied energy by the time it gets
to site, and the potential to contribute to a structure with an
effective zero net carbon footprint.
Timber as a construction material also adds value from
the very start of its journey. Not only does it fix carbon from
the atmosphere as it grows, it supports employment in the
forestry sector, it is lighter than other ‘traditional’ building
materials and therefore more energy efficient and less
costly to transport.
Continued from page 46
South African pine has the propensity to take up and store
between 600kg to one ton of carbon from the atmosphere per
cubic metre of wood.
Laws in South Africa regarding both energy usage and
energy efficiency in buildings were promulgated in 2011.
These apply not to the embodied energy of a given
structure, but rather to the performance of the structure in
how it consumes energy during its working life.
Both SANS 204: Energy Efficiency in Buildings and SANS
10400 Section XA: Energy Usage in Buildings sets clear
guidelines in place for the architect and builder on how to
provide for an allowable level of energy usage of a structure
through design and compliance with deemed-to-satisfy
requirements outlined by the National Building Regulations.
According to Jacques Cronje of Jacques Cronje Timber
Design, the more typical issues that impact on a
construction’s energy efficiency include the structure’s
orientation, window size and positioning, shading, material
choices with consideration for thermal and insulating
properties, solar heating, natural cooling and considerations
for natural light. The regulations take the performance of all
aspects of a build into account, including walls, roofs, water
heating and lighting, in line with requirements per climatic
zones in South Africa.
Cronje notes, “Non-masonry walls shall achieve a
minimum total R-Value of R2.2 in climatic zones 1 and 6 and
an R-Value of 1.9 in climatic zones 2, 3, 4 and 5. Insulation
of roofs is determined as the single biggest factor impacting
on energy efficiency [… and] the minimum R-Value of roof
assembly (such as all components of the roof and ceiling)
required in zones 1 and 4 is R3.7 with the other zones only
marginally less.
“Timber frame homes are included in the South African
National Building Regulations standards in SANS 10082:
Timber Buildings. When built to these standards, they also
48 FEBRUARY / MARCH 2019 //
CONSTRUCTION AND ENERGY EFFICIENCY
Wood is grown and is not a finite resource like oil or limestone,
and therefore timber as a construction material remains the only
truly renewable resource.
automatically achieve the standard required for registration
with the National Home Builders Registration Council
(NHBRC) and are easily designed to meet the requirements
of the recent energy efficiency regulations.”
ADDING VALUE TO THE
SUSTAINABILITY EQUATION
Other significant contributors to a timber construction’s
potential for high thermal resistance and energy efficiency
performance are its inherent thermal properties as well
as its propensity to take on bulk insulation and limit
thermal bridges.
According to Australian initiative Wood Solutions, when
considering the physical properties of wood, ‘Timber, a
naturally insulating material, makes for an excellent choice.
Air pockets within timber’s cellular structure create a
natural barrier to heat and cold.
‘Of all the timber options in construction, lightweight
timber is the best insulator overall as thermal conductivity
increases with density. In addition, thermal conductivity will
vary slightly with moisture content, residual deposits in the
timber such as extractives, and natural characteristics such
as checks, knots and grain direction.
See more on page 50
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