Timber as the dominant construction material for building: Part 1.

By Stellenbosch University

The question is, can (and should) locally produced wood materials fulfil this function in residential construction?

Construction contributes to around one third of global carbon emissions, so the way in which buildings are built is a really important consideration.

For our research into this subject we posed three basic questions we wanted to answer:

How does wood compare to competitive building materials in terms of environmental sustainability (in a South African context)?
What will the environmental impact be if we become a ‘wood building’ country?
Can we sustain a dominant residential wood building sector with local forest resources and services?

HOW WOOD COMPARES

Diagram 1.

For this research we started by looking at the biggest market for wood in South Africa currently, which is the roof truss industry. We looked at two different design houses – a small social house with a 42m2 footprint and a medium-sized house of 168m2.

We then considered the roof truss options that are available: pine, Biligom and light gauge steel. The team did a lifecycle assessment for each of these options, which is a very complex process as you need to evaluate the complete manufacturing process for each component right down to the source, so for example the source for steel is mining of metals. The results of this then determine what the overall impact of each process is that contributes to the material choice.

THE RESEARCH

The research covered 11 different impact categories and considered various factors (See Diagram 1)

If you take the impact of the three truss types we found that steel has a 30% higher impact than the wood options (Biligom or pine) on the small house. This was a particularly interesting, having the real data figures, to see this result as many manufacturers market themselves as green products.

Diagram 2.

Even more impactful is the medium-size house that shows light gauge steel has a 500% greater Global warming potential than the other options. All of the impact categories are equally important however, in the current environment climate change is a biggest challenge and considering this major factor in this one building component. Simply put, if you built a medium-sized house with steel roof trusses, you would add an additional 6 000kg of CO2 into the environment – a significant figure, considering that is only one building.

RESIDENTIAL BUILDING TRENDS

If we look at residential building activity in South Africa (see Diagram 2) from the period 2000 to 2016 you will note that in 2000, approximately 4 million m2 of floor area was built, and that increased to around 9 million m2 in 2007. This then decreased to around 5 million m2 in 2016. During this period, we built on average just over 54 000 houses, with the average house size being 114m2.

South Africa has a population growth of approximately 1.3%, but it is slowing, so we can expect that within 40 years, our population will start to decline. It is difficult to determine how many houses will be constructed in the next few decades, but for our calculations we worked on an average over this time, estimated an average requirement of 54 000 houses annually.

GLOBAL TRENDS

Considering building trends in other parts of the world using timber (see Diagram 3) you will see that between 1992 and 2017, South Africa’s wooden structure market share was basically 0. It is interesting to note that in Germany in 1992, there was a 6% wood-building market share and in 2017 this rose to 18%. In England it was also around the 6% mark and now it holds almost 30% market share. America has remained consistent over the period and wood-building accounts for just over 90% of market share.

Diagram 3.

In reality, what we expect being possible in South Africa is easily a 30% wood-building market share. Once again considering global warming potential (GWP) we compared different scenarios (see Diagram 4). If we could achieve a 10% wood-building market share for residential buildings the result would be up to a 6.5% saving on GWP, a 100% wood-building scenario could achieve up to a 71% saving on GWP. Now if you think how important buildings are in terms of global warming, these are serious and very positive numbers.