Integrating Sustainability Into Design Using Wood

This short course focuses on sustainability and design using wood. It covers a brief update on atmospheric CO2, an overview on building materials, available South African timber resources and finally design strategies which incorporate these aspects. It is aimed at architects, engineers and other built environment professionals in South Africa who want to explore the use of wood in structures, including residential buildings. We hope you will start your journey in wood here!

short course

How to complete this course

The course is open access and the content is available to anyone with internet access. This course should be completed in the sequence of the numbered sections. We make use of four components in our course (a) sections with text and illustrations, (b) video clips to explain some of the concepts, (c) a short online quiz after each section to test your acquired knowledge and (d) a test, available to learners who wish to obtain a certificate of completion. Please contact us at info@thewoodapp.com with the short course name to complete this test.
To make the course accessible to most people, we’ve tried to limit the time needed to complete it (an estimated 2.5 hours). This course will give you an overview of selected building materials impact and the environment, and design strategies to incorporate timber in a sustainable way. For in-depth knowledge on some topics you might require input from other sources such as national standards, material suppliers, selected textbooks, articles, etc.
If you have any questions or suggestions, please contact us at

info@thewoodapp.com.

Index

1. Introduction and Video (Vernon Collis)

2. An Update of Atmospheric CO2

2.1 A brief recap and overview
2.2 Where is all the CO2 stored?
2.3 The global scene and limiting temperatures
2.4 Quiz 1

3. Material Overview

3.1 Timber and the global environmental challenges
3.2 Understanding metrics to make a fair comparison between materials
3.3 Can South Africa provide the timber required to substitute masonry for housing?
3.4 Quiz 2

4. Shifting from Extracted to Bio-based Materials

4.1 Appreciating the challenges of specifying wood in construction
4.2 Wood compared to reinforced concrete, steel, and masonry

5. South African Grown Timber

5.1 Pine and Eucalyptus plantations
5.2 Pine and Eucalyptus species in South Africa
5.3 Quiz 3

6. Case Studies

6.1 Design strategies – considering 7 case studies
6.2 Quiz 4

Disclaimer
In the compilation of this module, free use was made of published information such as text, figures, drawings, tables, graphs, etc. As the use of such material is subject to copyright considerations, and the suitability and relevance of this content is in the process of being assessed, the content of this module is only reserved for personal use and the purpose intended. To adhere to copyright regulations, any publication of the module or parts thereof considered is subject to obtaining the necessary copyright agreement from the publishers by the author. Photographs taken and figures, drawings, tables and graphs generated by the author, are subject to copyright also.
Whilst all and utmost care has been taken to ensure the accuracy of the information contained in this module, no warranty can be given regarding the use, suitability, validity, accuracy, completeness or reliability of the information, including any opinion or advice.

1. Introduction

The language of architecture is to create forms and space. Architecture is largely limited to the devoted development of individual pieces of land, and the summation of their spatial and typological impact leads to transformation of our society. But these forms comprise massive volumes of building materials. Given the declining material resources and ecological challenges, architects and engineers need to extend their capacity to transform society by specifying appropriate building materials. By understanding both the local and the global impact of their choices and choosing responsibly, they can demonstrate the applicability of environmentally sustainable materials.
Unfortunately, in terms of material specification – particularly environmentally sustainable materials – the default of nearly all building designers is not progressive, favouring business-as-usual solutions without critical insight. This is not out of lack of will to innovate but because architecture suffers from complexity overload. To deepen their understanding of materials, architects generally turn to science and engineering, only to find the language of these disciplines exclusive and not documented in an accessible form. The result is that they often revert to suppliers who, naturally, promote their product over others without comparison and the training to critically assess its applicability. This makes it very difficult for architects to understand the consequences of their material choice.
For these reasons, providing architects with a new construction paradigm is difficult. The use of timber is a case in point. The South African construction industry is built on non-renewable concrete, steel, aluminium and masonry. Timber is usually limited to smaller building elements like trusses and decks. The only complete timber buildings are built by timber frame specialists who generally provide a design-and-supply service in typologies like log homes or vernacular clapboard housing.
As a result, timber has been relegated to the smaller scale structures; bigger structures being in reinforced concrete or steel. This is not because timber is a particularly limited material, but because bigger structures require specialists in the material. Compared to reinforced concrete and steel, there are almost no structural engineers specializing in timber apart from the pre-manufactured nail-plate truss industry (which is a highly regulated design-and-supply service) and timber frame housing.
Knowledge about timber construction in South Africa is not unified or being developed as in other industries. Here reinforced concrete (RC) and steel rule, and unlike in Northern Europe, this is what local tertiary civil engineering academies traditionally teach. Timber is largely being excluded in South Africa, but the expertise and support is available, although not at all as readily as RC and steel. Notwithstanding this, architects and engineers correctly specifying sustainably grown and harvested timber using our current knowledge and expert base, can contribute to reducing Green House Gasses (GHGs) and addressing resource depletion and thus the protection of our planet’s future.

2. An Update of Atmospheric CO2
2.1 A brief recap and overview

The fluctuations in atmospheric carbon dioxide (CO2) over the last 500 million years have generally reflected the evolution and subsequent increases and decreases in plant growth on our planet; plants have been powerful agents of global environmental change due to their impact on CO2 levels. CO2 is thus a common and helpful measure of general climatic conditions. We live in an age when the escalating influence of humankind on the environment is only too apparent; the human footprint being so dramatic that a new term has been assigned to our present geological epoch – the Anthropocene. Trees, as ever, should be at the heart of the climate change and resource depletion discussion. The sum of evidence, plus common sense and basic biological theory suggest that the more forests we retain and the more forests we plant, the better.
The Anthropocene has resulted in current atmospheric carbon being about 420 parts per million (ppm). The latest scientific studies dictate that we need to reduce this to 350 ppm to avoid runaway climate change (climate.mit.edu). “Business as usual” could result in 1000 ppm by the end of the century. Clearly “business as usual” needs an immediate and serious review. There is no silver bullet and the “Wedges” strategy (Pacala, S. & Socolow, R. 2004) proposes that each sector (Figure 1) has a part to play and that the sum of the increments would be effective (Walker, G. & King, D. 2006).

Figure 1: Wedges strategy showing the influence various approaches may have on reducing atmospheric carbon (parts per million) to acceptable levels (Adapted from Pacala & Socolow 2004).

The goal of maintaining our temperature rise by significantly reducing CO2 emissions requires a concerted effort from all sectors – the construction industry being a significant contributor to the problem. At present, the manufacturing of concrete, steel and bricks consumes 16% of global fossil fuels. Add transport of materials and this figure increases by up to 30%. Over 90% of the weight of material transported annually in the USA is attributed to the construction industry (Chadwick, O. et al 2013). A shift away from these materials is imperative and particularly to lighter and sustainably harvested timber. In this regard South Africa is ideally positioned with a world-class timber plantation industry. Developers, architectural designers and engineers favour concrete and steel over timber, and in many cases specify imported woods from natural tropical forests. Specifiers and designers of the materials applying good science is critical if South Africa wants to make a real contribution to the global environmental challenge.
But statistics always require a critical commentary. For example, the fuel used to transport heavy building materials gets included in the “transport sector”, and the energy used to manufacture the materials is represented under “energy supply”. This means that buildings in the IPCC (2011) study unrealistically show that buildings only produce 8% of the Green House Gasses (GHGs). One statistic which is difficult to redistribute is “deforestation” (Figure 2), and the annual loss of our natural forests, a critical carbon sink, contributes almost 18% to effective GHG emissions (Walker, G. & King, D. 2006).

Figure 2: Pie chart showing the total percentage green-house gas emission per sector (IPCC 2011)

Thus, the materials that we choose to build with can have a significant effect on GHGs (CO2 being a major component and common climate change measure), resource depletion and biodiversity reduction. Sustainably grown and harvested timber is an obvious choice, given that wood is essentially “made” from CO2 naturally photosynthesized from the atmosphere; the gas that is threatening humankind is converted into a building material naturally.

2.2 Where is all the CO2 stored?

Starting about 350 million years ago when life started to flourish on land and in the sea, animals and plants processed and stored CO2. Sea life used CO2 and calcium to form their exoskeletons and shells (calcium carbonate – CaCO3) which eventually fell to the bottom of the sea. Through a geological process over eons this “boneyard” was converted into limestone rock (also CaCO3). Today limestone makes up about 80% of all fossilized CO2 (Figure 3). We mine and burn it to make lime (CaO) and cement. This firing releases the ancient stored CO2 back into the atmosphere.

Figure 3: Effectively all our fossilized CO2 was captured and stored 100s of millions of years ago via natural processes. We mine and process these materials releasing the ancient captured C02 back into the atmosphere.

The other 20% of stored CO2 is found in oil, gas and coal. Coal mainly formed from ancient forests which collected in swamps and were trapped and sealed by a global extinction event until we started to mine it during the industrial revolution.
Oil was formed when dead sea-life such as algae and plankton gravitated to the bottom of the seas and mixed with silt and clay deposited by river mouths, which over eons formed sedimentary rocks. We mine these rocks today to extract the fossil fuels oil and gas which are burnt to make cement, steel and aluminium.
Life processes sequestered (captured and stored) CO2, and so do our forests today. This is the basis of the argument for preserving and extending our indigenous forests, and for responsibly developing plantation forests thereby potentially sequestering the dangerously high volumes of CO2 in today’s atmosphere.

2.3 The global scene and limiting temperatures

If we want to keep the global temperature rise to below 1.5o Celsius, by controlling GHG emissions and related CO2 release, we need a shift to making buildings, and where appropriate, structures, from appropriate timber and not from concrete, steel and bricks (Chadwick et al 2013). However, one also needs to consider aluminium. This material produces 5% of the world’s GHGs and in buildings competes with timber, typically in the manufacturing of doors and windows (IPCC 2011). Thus, substituting this material would further address the argument.
If this research is extended globally, the figures are indeed startling. Chadwick et al’s study of 2013 shows that only 20% of the world’s annual timber growth is harvested per annum. The majority is for energy use, particularly in the developing countries. The other is for the construction industry and wood products, including paper, but this pulp demand is fast reducing as the digital age gains momentum. If the sustainable harvesting of timber is increased to at least 34% per annum, and the tree residue and production waste is used for energy (to replace coal/oil/gas), then GHG emissions can be reduced by up to 19% globally (Chadwick et al, 2013). This is feasible by substituting concrete, steel and bricks accounting for the massive development boom expected in Africa and Asia.
However, Chadwick’s suggestion of increasing sustainable harvesting of timber from forests is much easier to achieve in the colder climes of North America where control measures are in place and biodiversity is relatively low compared to the tropics (Figure 4).

Figure 4: Map showing where the vast majority of forests with straight “structural timber” trees are found. Tropical forests are homes to the greatest land biodiversity on the planet. Timber from these regions must not be specified.

The highest biodiversity on the planet occurs within the tropics where the forest growth rate is the highest, and unfortunately where governmental control of these forests in most parts is at its lowest (Packham 2012). So, their advice must come with a warning, and that until the tropical countries can demonstrate best practice sustainable planting and harvesting, timber must not be purchased from these regions.

2.4 Quiz 1

1. Name the two largest green-house gas emitting sectors
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3. Material Overview
3.1 Timber and the global environmental challenges

Conventional sustainability is divided and assessed under social, economic and environmental categories. This course deals with only the environmental aspect of sustainability. The environmental impact of any design decision should be considered under the three legs or sub-categories: pollution, resource depletion and biodiversity reduction (Figure 5).

Figure 5: The three legs of environmental sustainability required for thorough life cycle assessment

Figure 5: The three legs of environmental sustainability required for thorough life cycle assessment

Atmospheric carbon dioxide, one of the most common climate change indicators, is due to pollution. Focussing on CO2 is a good starting point, but we need to continually consider the other pollutants, viz. resource depletion and biodiversity.

Example:

A suspended floor can be designed and built from reinforced concrete, steel, SA Pine, imported timber or combinations of these materials. A true evaluation of the suspended floor example requires a proper Life Cycle Assessment of not just the carbon footprint aspect of pollution, but in all three sub-categories – pollution, resource depletion and biodiversity.
The impact of the selected material needs to be considered from extraction (mining) or harvesting through processing, manufacturing, transport and construction, to the performance of the material during its service life and finally to its reuse when its serviceable life comes to an end, for the location in question. Measuring the carbon footprint on its own does may not give the true picture and can result in inappropriate design and specification decisions. Life-cycle assessments should only be completed by a specialist environmental practitioner. A basic indication of the carbon footprint of building materials can be found on the Institute of Civil Engineers’ (UK) database (http://circularecology.com/embodied-carbon-footprint-database.html).

It is possible within the foreseeable future that the atmospheric carbon emission challenges may be partially solved via carbon-capture and storage (CCS) at the source, for example, in cement production, more effective renewable energy technologies and new material technologies such as graphene replacing steel and/or more energy efficient technologies, such as improved steel production processes. If so, this still leaves the existing CO2 in the atmosphere, the balance of the pollution, resource depletion and biodiversity reduction challenges. Sustainably grown, harvested and processed timber and timber products can assist with all the challenges, with the aim to enable a shift to a more circular renewable material economic system.
For this to happen, the entire global timber chain from sustainable forestry to timber product manufacturing, to design and specification, to research to construction and recycling would need to be upgraded to compete with that of the steel, concrete and masonry industries.
Making appropriate sustainability design decisions requires expertise in materials’ Life Cycle Assessments (LCA). LCAs are not yet in the main stream in South Africa, and apart from the energy use after the construction component, neither are there any Regulatory LCA compliance requirements. Without it being a legal requirement, it means that fully considered LCAs are mainly driven by ethics, international trends and supported by consultants and contractors with special interest in environmental sustainability. Until local LCA specialisation is developed further, and updated Regulations are promulgated, the responsibility remains with the designers, specifiers and contractors to perform relevant LCAs.
However, now, the teaching institutions, the industry and the regulatory framework are not properly geared for timber construction, and the designer must remain critical when assessing materials that are specified based on LCA metrics. Architectural and civil engineering design is a complex process, containing a range of site and location specific constraints with LCA adding another layer of complexity to a design. However, where appropriate, sustainably grown and processed timber properly specified, addresses the pollution, resource depletion and biodiversity reduction challenges better than any other building materials.

3.2 Understanding metrics to make a fair comparison between materials

There are arguments against timber using “thoroughly” researched statistics, particularly from the well-established industries with which the material competes, viz. steel, concrete, bricks and aluminium.
The Carbon Footprint arguments are reduced to scientific measurements (metrics) and how equivalent comparisons are made between the various materials. And herein lies the heart of the debate – this comparison requires an in-depth discussion and explanation because it is these comparisons that are manipulated by the suppliers to confuse the market, and particularly the designers specifying the materials.
The majority of materials used in the construction industry are directed towards buildings, a sector that is generally led by developers and their architectural designers. In order for these designers to deepen their understanding of “green” building materials, they turn to science and engineering only to find the language of these disciplines exclusive and not documented in an accessible form. This makes it almost impossible for these designers to interpret information and make a socially responsible decision. The net result is that they often revert to suppliers who naturally promote their product over others without comparison or using selected “statistics” that favour their material or process.
There are various metrics used to measure and compare materials and processes, the most popular one being the embodied carbon dioxide (often referred to as “carbon footprint”). An LCA that is a “full” Life Cycle Analysis (or cradle-to-grave analysis) is more accurate as the carbon footprint relates back to fossil fuels consumed and thus emissions produced to extract the materials needed to manufacture the product (even if these are waste products). Equivalent embodied CO2 is also used as a metric where other gases are produced in a material’s life cycle. These harmful products are given an appropriate weighting (factor) to make the assessment in terms of CO2 only; making it easier to compare “apples with apples”.
The limited embodied carbon comparison is used here to illustrate how the metrics selected can give a very different impression of the carbon footprint of the material, which can influence the designer to come to an incorrect conclusion with regards to material choice.

Figure 6: A comparison of the CO2 footprint of common building materials using mass (ton) and the metric (IPCC Sustainable Sites Handbook)

Material comparisons, whether measured by mass, volume or application will give very different results. It is therefore critical that a designer fully understand these distinctions in order to make an effective and socially responsible material choice.

Example:

Consider a comparison between concrete and sawn timber (Refer to chart below):

If mass is used (measured in kgCO2/kg, being the mass of CO2 emitted to produce a kilogram of the material), concrete is more sustainable than timber by a factor of 3.5 (although this may be surprising, concrete is mainly made up of aggregates (sand and stone) which have a very low carbon footprint. It is cement’s vast global consumption that adds up to give it such a large carbon footprint).

If volume is used (measured in kgCO2/m3, being the mass of CO2 emitted to produce a cubic metre of the material) then concrete is approximately the same as timber.

If the application of the material is considered, for example a suspended reinforced concrete slab and a suspended timber floor supporting the same loading (live load) over the same span are considered (this is the only fair and truly scientific way to make the comparison), then timber outperforms concrete by a factor of about 4. The reason is two-fold: firstly, the majority of the concrete slab strength is dedicated to carrying its own weight. Secondly a typical timber floor is 16 times lighter than a RC slab and 9 times more efficient in terms of strength-to-weight ratio.

The CO2 sequestration of timber is rarely included in the comparison calculation as it is assumed that the wood product will eventually decay (buried) or be burned at the end of its life. If designed properly, timber can be reused many times, particularly the heavier structural members (beams, columns and joists), for example the recycling of Oregon Pine flooring, joists or truss members that are recovered from Victorian buildings constructed in the late 1800s.
In such cases, if the carbon stored by the wood is added to the equation, then the suspended timber floor becomes carbon negative. This example only considers CO2, and although reasonably indicative, a full Life Cycle Assessment needs to be considered to make a properly informed decision. For example, and as compared to cement, sustainably grown, harvested and specified timber is a circular renewable resource, and where timber such as Balau or Meranti sourced from equatorial natural forests are not.

3.3 Can South Africa provide the timber required to substitute masonry for housing?

Philip Crafford and Brand Wessels of the Department of Forest and Wood Science (Stellenbosch University) investigated South Africa’s log (roundwood) resource availability and the potential global warming impact of an increasing wood-based residential building market. Their research showed that currently 24% of industrial roundwood (essentially the tree trunks) is processed by sawmills to make timber sections mainly for the construction industry. The majority of the balance goes to pulp and board mills (51%) and chips (17%) exported as an energy resource (Figure 7).

Perception of defects occurring in the primary building materials warrants some reflection. If any structure built from reinforced concrete, steel or masonry develop defects, the contractor or the designers are blamed. Comparatively, if any wood develops defects, the material is blamed. However, most timber failures are attributed to poor design, specification, selection and construction of timber and not the material itself. The available expertise in RC and steel far exceeds that of timber by a massive margin. This is a common reason why timber is blamed by appointed designers when its performance does not meet expectations.
Unlike the USA, Canada and Northern Europe which have a timber culture developed over many centuries, South Africa has developed its building culture around RC, steel and timber. So, what timber does South Africa have?

Figure 7: South African round-wood consumption by sectors

Furthermore, “with the use of wood resources currently exported as chips, as well as planting trees in areas that have being earmarked for afforestation, a sustainable residential building market, where all constructions are wood-based, is possible. However, in the short term, imports of wooden building components might be necessary if rapid growth in wood-based buildings occurs. Basic modelling analyses show that if the market share of wood-based buildings increases to 20% of new constructions, the embodied energy and global warming potential of the residential building sector could decrease by 4.9%. If all new constructions were wood based, the total embodied energy and global warming potential of the residential building sector could decrease by up to 30%” (Crafford et al 2020).
Their findings include that about 70% of local residential trusses are wood-based but only 1% of new residential houses can be described as wood-based structures. In countries like the USA, Canada and Australia, well over 90% of residential housing is timber frame.
Imported timber should be sourced from sustainably grown and harvested plantations such as those in Brazil, Argentina and Germany. Research will however be required to quantify the environmental impacts of importing these materials to South Africa. Research from other countries has shown that where shipping is over short land transport distances, the environmental impact of timber imports can be significantly reduced.

3.4 Quiz 2

1. Name two low CO2 footprint materials
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4. Shifting From Extracted to Bio-based Materials

4.1      Appreciating the challenges of specifying wood in construction

In the interim, and to enable a shift from mined and processed materials to bio-based materials, designers need to be aware of the challenges of designing and building in timber, being the biggest proportion of bio-based construction materials in South Africa, and develop appropriate strategies for each project.

Design strategies to consider

  1. Build a team with the right experience and design skills: Although limited in number, timber design specialists do exist in South Africa.
  2. Consider timber for only the right applications: Wood, like all materials, has performance constraints. Include these as design constraints from stage one of the design process rather than consider timber once the scheme has been developed to stage three – the material informs the design rather than the other way around. Even reinforced concrete or steel used inappropriately can age rapidly.
  3. Use engineered timber products: Be aware of availability of the range of engineered timber products. Use the technologies appropriately. It is not uncommon to hear a client or designer blame the poor performance of an SA Pine Grade 5 beam when a laminated beam was the appropriate specification, or when an exposed laminated beam was specified outdoors and the material blamed when the timber delaminates.
  4. Apply appropriate design strategies: Timber is not a one-to-one substitute for steel, aluminium or brickwork. Design with the material in mind from the outset.
  5. Develop the right detailing: Timber detailing is an art and is well documented. Like steel, the devil lies in the detailing of the structural joints. The steel industry gets around the problem by the steel contractors providing shop drawings. The timber industry has yet to develop an equivalent process. Here the appointed structural engineer has to provide the shop drawings. This has for the large part kept many structural consultants away from projects requiring such detailing, often recommending steel or reinforced concrete instead – material with which they are comfortable.
  6. Source the right contractors: Specialist timber contractors can assist with detailing. It follows that it is critical to employ the appropriate contractors during the design stages and together consider the appropriate timber technologies from the range of engineered products available.

Other advantages and disadvantages of using timber: Notwithstanding timber’s much lower Life Cycle footprint and that it is a renewable resource, other advantages of timber include its superior thermal insulation performance and that it is significantly lighter (self-weight) than concrete or masonry. This relates to inter alia lower transport costs, much smaller foundations, significantly better seismic performance (as this is directly proportional to buildings self-weight) and quicker erection and deconstruction time and effort.

The disadvantages of timber include acoustics as special care is required to address sound transmission through suspended floors. Perceptions around the fire risk of timber structures are not well-founded. Fire standards were developed to limit and control the spread of fire and to provide a period for the occupants to safely leave the building, as well as time for the fire brigade to extinguish the fire, and not to avoid any structural damage. In any serious ground floor fire, for example, the suspended floor above, whether of RC, steel or timber, will probably be lost.

External timber has limitations around wetting and drying cycles as well as fungus and insect attack. The experienced timber specialist will design the environment (e.g. correct roof overhangs) and specify the correctly treated timber to address these challenges. The challenges of designing and specifying in timber are covered in brief in the Case Studies and in more detail in other TheWoodApp CPD courses.

4.2. Wood compared to reinforced concrete, steel and masonry

Reinforced concrete: In South Africa reinforced concrete (RC) is the structural building material of choice. The majority of our medium to large building structures are built from RC (foundations, frames and suspended slabs) with the design engineers providing the detailed reinforcing steel (bending) schedules. The cement and concrete industry is well organized – from tertiary education to consulting and construction – with most structural engineers being RC design specialists. They are supported by thorough National Standards, numerous CPD courses, cement and concrete material specialists and suppliers, material testing laboratories and well-established due processes to achieve compliance. The contracting industry provides the necessary expertise to manage and build with concrete and understands the due processes in order to meet specifications. In some instances, such as precast and pre-tensioned slabs, the industry provides design-construct packages.

Steel: The steel industry is similarly well organized. Most steel buildings are industrial and commercial shed structures such as portal frames. The steel industry provides a design and erect service but unlike most reinforced concrete buildings, an entire shed structure can be premanufactured and transported to site for erection. Generally, the in-house design engineer specifies the overall structural sizes and joint configurations with the steel contractor developing the detailed shop drawings for the structure. Unlike RC, drawing up shop drawings requires practical knowledge of the material, jointing, performance and tool sizes required to manufacture and assemble the joints and structural members. Practical engineering experience is thus required to configure a safe, buildable and compliant structure.

Both RC and steel are primary engineering materials and are well covered at all tertiary institutions in South Africa. A civil engineering graduate would have the necessary foothold to start off as steel or RC structural engineer (note: masonry is not covered in the engineering curriculum; an engineer have to self-train or be mentored to gain the required competence).

The net result is that the RC and steel industries have the capacity to deliver highly engineered structures built on a well-developed material system and culture from mining through processing to the end product. The same does not apply to timber. A civil engineering graduate has not been trained to design or build in this material. Compared to steel and RC, there are practically no timber engineers with a similar level of experience and skills.

Timber: As in masonry, timber is lightly covered, if at all, in tertiary engineering education. Timber also requires structural engineers with a special interest in the material to develop competency. Currently, timber structures occupy the niche markets of premanufactured nail-plated timber trusses, suspended timber floors (internal floors and external decks), timber frame buildings (mostly houses) and poles for agricultural and game reserve structures. The products are not yet engineered to the same degree as RC and steel. Should a developer want a multi-storey building structure, a shopping centre or an industrial portal frame shed built from timber, they will be hard pressed to find an architect and more so a structural engineer with the requisite competence to design and specify the timber system, and equally hard pressed to find a specialist timber product supplier or timber contractor to deliver the end-product in South Africa.

Current availability of engineered structural timber products: Grade 5 (a flexural strength of 5 MPa) is the entry point and most common SA Pine structural grading which can be engineered up to gain better performance characteristics. Grade 7 (or Grade 9 depending on the experience of the timber specialist) members can be selected from the Grade 5s, these superior grades having a higher density and strength with less inherent defects such as knots. These can be finger jointed to make longer sections or laminated to make larger and longer higher graded laminated beams and columns, the laminated sections generally made to standard sizes and off-shelf. In terms of the day-to-day market, apart from the premanufactured nail-plate trusses, that’s where it stops. Anything else is purpose made if the expertise is available.

To find an engineer and a supplier who can design and make up a laminated (with curved haunches) portal frame structure would be significantly more difficult, if at all available, than a similar one in steel. It would also be equally difficult to find a team to design and supply simpler plywood box beams or flitch plate sandwich beams. But it hasn’t always been like this. In South Africa in the 1970s and ‘80s, there was a big shift to timber and the structural design and construction industry geared itself to deliver such products, the initiative supported by timber specialists from the Universities of Cape Town and Pretoria (see Case Study). For complex reasons, this initiative was outcompeted by the concrete and steel industries and did not sustain beyond the early 2000s.

Demand and supply: Developing the timber industry reduces to a question of demand and supply. If the demand exists for timber buildings, then the market forces will respond with supply and in turn so will the professions and the academies respond. Architects and engineers are in the best position to influence their clients, and if they skill themselves in the interim, as they did in the ‘70s and ‘80s, then the required level of engineering and support will follow. This will shift the current position of RC, steel, masonry and the timber niches forming the backbone materials of Southern Africa’s building culture.

5. South African grown timber
5.1      Pine and Eucalyptus plantations

In order to meet the demand for structural timber (mainly for mining) an international standard forestry knowledge base was developed in this country and is considered a world leader in the discipline. Most of our plantation forests were developed in grasslands and in mountain fynbos in the Cape. Compared to our international economic competitors, South Africa has almost no natural forests. Our plantation forests are more than double the size of our indigenous forests, and these plantations annually absorb the equivalent amount of carbon produced by the manufacturing of cement, steel and aluminium (Coppen, H., 2012).

Eucalyptus and Pine are two important “crops” to consider. Both have gained a poor reputation because of the damage that alien trees have caused to the environment due to their perceived water demand and their capacity to invade pristine indigenous environments. Once again, the metrics and the method of comparison require consideration.

Firstly, plantations must be considered a crop since they are planted and harvested much the same as fruit tree orchards, vineyards, sugar cane or wheat. If considered a crop, then they outperform other crops in almost every facet: water demand, land use, insecticides, pesticides, fertilizers, and so on. Farming in South Africa utilizes 14% of the land and forestry only 1% (Godsmark, R., 2010 & Figure 8). In terms of water, forestry uses no piped water as compared to farming which uses 63% (Coppens, H. 2013).

Figure 8: Map showing land-use in South Africa. Plantation forests use 1% of the area.

Naturally, all trees access the ground water and can reduce the stream flow. Our riverine catchments have been infested by thirsty exotics like wattle and hakea which are choking the system (Moll, E., 2013). The water demand characteristics of an unmanaged invasive, however, must not be extended to broadly include all managed non-invasive exotics. This assumption requires a comparison between a Radiata Pine plantation in the Cape, a vineyard in the Cape and Fynbos (refer to Figure 8 above). Comparing water usage and carbon captured, a Radiata Pine plantation out-performs a vineyard in every respect. Compared to fynbos, Pine has significantly higher carbon storage to water use efficiency ratio if the pine is used for timber products and not left to rot and convert back to carbon. However, this is only a carbon perspective and the legs of biodiversity reduction must be carefully considered. Humanity has worked itself into a difficult corner where the development for 8 billion people must be balanced with environmentally sustainable strategies, which includes making some compromises for overall success. In this context, 1% of South Africa’s land dedicated to forestry as compared to 63% for agriculture seems a reasonable strategy.

5.2      Pine and Eucalyptus species in South Africa

There are many species of Pine in South Africa and, like our major food crops, were imported from the Americas and Mediterranean Europe. The quality between the species is significant, the best structural timber coming from Pinus Radiata or “Monterey Pine”. Compared to Pinus Elliotti, for example, Radiata is a very different material, and the fact that both are referred to as SA Pine does no justice to either. Unfortunately, there is no differentiation between species when a Grade 5 SA Pine beam is purchased. A more detailed specification from the designer (knot free for example) is not usually provided as the emphasis is on the strength grade.

Figure 9: A range of some of the pine species that grow in South Africa. They were imported from Eurasia and the Americas mainly for structural timber and landscaping. Only some are invasive.

All our Eucalyptus species were brought from Australia. As in SA Pine there is a broad range of species being grown with significantly different performance characteristics such as strength, durability and stability. Karri Gum, for example, makes for a very stable and hard-wearing T & G floor. Sugar Gum is a very strong structural timber with correctly selected and prepared samples providing flexural strengths well in excess of a Grade 10 timber. However, such timber is seldom available off-shelf and require expert input and experience from both the designer/specifier and the timber miller to make appropriate determinations. The Eucalyptus hardwood is known to be strong and has a propensity to deform if not selected, cut and prepared properly. This has unfortunately given this hard wearing and strong timber a relatively poor reputation. It is expected that this will change as the industry chain shifts more towards timber products.

Figure 10: A range of some of the Australian Eucalyptuses that grow in South Africa. They were grown for the gold mining structural timber (props), farm wind breaks, shade and structural timber. Many specimens are over 100 years old. Only some are invasive.

There is still a trend to put imported exotic timber ahead of our local timbers and only because of perception driven by aspiration (it is not well known that South Africa has an exceptional forestry culture and knowledge base supported by a sound forestry and timber industry). Timbers like Balau and Meranti are preferred which are harvested from pristine tropical forests in South-east Asia, and so much Balau was “mined” in Laos that very little of their forests remain (National Geographic, 2011).

5.3      Quiz 3

1. Name four timber design strategies, to consider
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6. Case Studies

6.1      Design strategies – considering 7 case studies

Three key strategies presented in the case studies require careful consideration by the designers:

  • Using sustainably grown SA timber products to replace imported timber: An example is the specification of SA Pine or Eucalyptus decking instead of Balau which is imported from East Asia and extracted from the rain forests such as Cambodia. Some imported timber have been sustainably grown and harvested and need to be considered where appropriate. However, it takes much research and investigation to ascertain this fact. The optimum is to appropriately design, specify and build with our locally available plantation timber and their engineered derivatives.
  • Using sustainably grown SA timber to replace conventional building materials: Where appropriate, less environmentally friendly materials such as masonry, steel, various synthesized board products and reinforced concrete are substituted, for example, by timber frame instead of masonry walling, nail-plated timber instead of steel trusses, timber beams and joists instead of reinforced concrete suspended floors.
  • Using recycled timber and off-cuts: Although this forms only a small portion of the total timber turnover in the industry, it does make a CO2 reduction contribution, raises awareness, facilitates design and construct habit changes and gets the designer and builder to reflect on how best to design a new building so that it can be easier to renovate, or so that its materials can be easily recovered for reuse at the end of its life.
  • The case studies presented employ a combination of the above three strategies to shift to locally grown and processed timber products. SA Pine and Eucalyptus make up the vast majority of the structural timber products used in South Africa. Imported timber, mostly from the tropics, makes up the largest portion of timber used for doors and windows and upmarket residential and commercial decking. The first case study is therefore fleshed out as a best practice example and to dispel myths around our local timbers.

    Case Study One: SA Pine external timber decking (Ballito, Natal)

    32 mm SA Pine decking installed in place of Balau or similar unsustainable hardwoods (Photo 1). Balau is cut from old growth tropical forests in Southeast Asia, particularly Cambodia, causing massive environmental destruction and biodiversity reduction. Specifying Balau for decking is akin to specifying rhino horn or elephant ivory for door handles.

    Photo 1: SA Pine decking “before” and after about 5 years of service. The wood was not finished and greyed naturally. No light sanding has been required to address any edge splintering.

    The summarized specification for the deck included:

    108 x 32 mm SA Pine finger jointed H3 CCA treated decking planks fixed with two stainless steel c/sunk screws per joist. Screw holes in decking planks to be 1.5 mm larger than the c/sunk 5 mm screw shank to allow for wetting and drying expansion and contraction across the width (grain). The plank drill holes are not to be countersunk as countersunk screws will pull into dry SA Pine. Decking not to be laid wet but given sufficient time to dry after H3 treatment.

    Note: CCA (Copper Chromium Arsenate) treatment involves impregnating the timber with a mixture of copper, chromium, and arsenic compounds, which provide long-lasting protection against decay and insects

    Joists spaced at 450 mm centres (max 15 x plank thickness instead of 20 x thickness as per SANS 10 080). By comparison a 22 mm thick SA Pine section is too thin to achieve satisfactory performance and an economically acceptable life span.

    The joists too must be stiffer than the SANS minimum requirements. Recommend that a live load of at least 2.5 kN/m2 used to determine the joist structural sizing and spacing. All joists to be continuous over supports. Use finger joints or splint reinforce simply supported joints to create a continuous section.

    The SA Pine was lightly sanded with no finish treatment. The CCA treatment increases the hardness and the abrasion resistance of the timber. Maintenance requires light sanding when and as required over the years. Pine will lose its green CCA stain and grey over time, and eventually look very similar to Balau. SA Pine splintering is far less severe than the hardwoods. The H3 CCA treatment will also give a longer life than hardwoods which cannot be treated to the same degree as SA Pine softwoods.

    Hardwoods are generally much harder and stronger than softwoods like SA Pine. Thus, thinner hardwood sections are required. However, the higher structural bending strength means that it is equally much stronger when it warps as it ages following the seasonal wetting and drying cycles. It is not uncommon for such movement to shear the fixing screws and for uncontrolled movement. SA Pine, being weaker, is much easier to fix and control with properly selected fixing screws.

    Case Study Two: Internal Karri Gum flooring on suspended timber first floor (Cape Town):

    22 mm Karri Gum (Eucalyptus) T & G flooring was applied to a domestic first floor, with the Karri Gum exposed as the finish wearing surface (Photo 2). The boards were fixed on rubber strips on 47 x 32 Grade 5 SA Pine battens placed at 250c/c on rubber mountings on recycled Grade 7 Oregon timber joists at 450 centres. Rubber cut from recycled  vehicle inner tubing to insulate solid-to-solid sound transmission. Voids were sound insulated with recycled carpet underfelt off-cuts rolled and packed into place.

    Photo 2: Recycled Karri Gum 22 mm flooring (right hand side) on rubber on SA Pine G5 counter battens with rolled underfelt void sound insulation.

    Karri Gum flooring was recovered from a demolition project. Timber originally cut from Karri Gum plantations in the Southern Cape.

    Karri Gum is an extremely hard wearing and durable hardwood. It does not need an epoxy or similar finish to enhance its abrasion resistance against high point loads such as chair and bed legs. Softwoods such as SA Pine do need an epoxy finish to improve its durability and abrasive resistance.

    Case Study Three: Doors and windows in Centani (Eastern Cape)

    Windows made from SA Pine in place of Meranti or similar imported hardwoods (Photo 3). Most Meranti is cut unsustainably from the natural protected forests in Southeast Asia.

    Windows were engineered from H3 CCA treated Grade 7 SA Pine softwood sections. Thicker sections were used compared to conventional hardwood timber windows. The Grade 7 timber was stacked and left to dry for three months after treatment. The straightest sections were selected and machined (about 10% of the timber had warped and were cut to make shorter window sections). The cut sections were left for four weeks to achieve the ambient moisture content and the best sections selected. About 5% of the cut sections were rejected because of warping and were cut to make shorter window sections. The timber “vierendeel frame” window structure included horizontal struts (no large panes) to restrain possible seasonable movement once the window is built into brickwork. The environmental design for the windows and doors includes appropriate roof overhangs to protect the windows from the rain, wind and sun.

    Photo 3: Doors made from a SA Pine sub-frame clad with Grandis boarding; windows from selected Grade 7 SA Pine.

    The external doors were engineered from 47 mm thick H3 treated SA Pine Grade 7 “trussed” sub-frames clad with 12 mm boron treated and sealed locally harvested Grandis (Eucalyptus) planking. All doors and windows were painted to limit the seasonal moisture variations.

    Case Study Four: Doors and windows in Koidu (Sierra Leone)

    Doors and windows made from SA Pine in place of aluminium or local timber harvested from the rain forests (Photo 4).

    The doors and windows were engineered from H3 CCA treated Grade 7 SA Pine softwood laminated sections. The treatment protects the timber mainly from the very aggressive insect attack that is prevalent in tropical West Africa, as well as fungal attack. Traditionally, the locals unsustainably harvest local hardwoods and treat them with diesel.

    Photo 4: Doors and windows made from selected Grade 7 laminated SA Pine. Internal shutters of 22 mm plywood.

    As per the previous Case Study, thicker sections were used compared to conventional hardwood timber windows. The Grade 7 timber was stacked and left to dry until equilibrium was reached with the ambient moisture content. The straightest sections were selected, machined and laminated (two laminations were used which stabilises the timber). The timber window structure was designed to include struts to control possible seasonable movement once the window was built in. The doors and windows were stained and then varnished to limit the high season moisture variations.

    Case Study Five: Laminated SA Pine portal frame (Wits University, Johannesburg)

    The Wits University Sports Hall built in the 1970s includes a laminated timber portal frame structure. In the ‘70s and ‘80s timber engineering was becoming more mainstream but was eventually eclipsed by the steel industry in the late ‘90s. There are very rare and select engineers and manufacturers who currently have the skills to design and manufacture such structures.

    Photo 5: Laminated SA Pine portal frames at Wits University Sports Hall. This is the highest level of timber engineering, substituting for steel.

    Case Study Six: Sugar Gum pedestrian bridge (Newlands, Cape Town)

    The original old timber pole bridge had come to the end of its life. The SA Pine poles were incorrectly treated externally with creosote leaving the internal timber exposed to insect and fungal attack, particularly at the drill holes and splits. The owner’s natural reaction was to have a bridge of steel. The bridge, however, was made entirely from Sugar Gum harvested locally (recovered by Universal Timbers) as many of the Western Cape farming windbreaks comprising this straight growing, stable and durable hardwood were felled towards the end of their lives (Photo 6).

    Photo 6: Newlands pedestrian bridge “before” and six years on. Sugar Gum was carefully selected, cut, prepared and bridge designed within the performance limitations of the Eucalyptus timber. The timber was not treated and has naturally greyed over time. There has been no noticeable movement in the timber.

    The bridge beams were of approximately 9 m long solid Sugar Gum sections (spliced SA Pine was a backup option considered). Additional decking and balustrade sections (cut and machined from Sugar Gum) allowed for selection of the best pieces and to allow for “spare” replacement sections should any of the decking planks or uprights warp unacceptably after erection. 6 years on and there has been no excessive warping or splitting. No treatment was required with the timber being left to age to a natural grey. Indeed, Sugar Gum is so hard it is very difficult to treat such old dense sections, if at all.

    Case Study Seven: SA Pine industrial trusses (Koidu Mine, Sierra Leone)

    SA Pine premanufactured trusses can comfortably achieve the large spans required in inter alia industrial sheds, halls and in commercial applications. The advantage is that they can be assembled on remote site where transport is a challenge, as were the large span timber trusses built in Koidu.

    Photo 7: Large span trusses can be made of either steel or timber. The perception that timber limits trusses to short spans is incorrect.

    The perception of SA Pine being a fire hazard and that it cannot manage large spans is incorrect. SA Pine is combustible but not flammable. In industrial fire which spreads to the roof, both steel and timber trusses would need to be replaced; the issue being to provide enough time for those occupying the building to escape. Steel deforms and buckling under a heat load, and timber eventually ignites. Heavier timber sections maintain their structural stability for a longer time than a relatively thin section steel truss when subjected to the same fire load.

    Othe case studies:

    The reader is encouraged to the more common examples of timber frame housing replacing masonry and the modern trend of build multi-storey structures from CLT.

    6.2      Quiz 4

    1. Name four different timber design applications
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    References

    BBC Panorama 2011, Jungle Outlaws – The Chainsaw Trail (Congo), BBC 2011

    Beerling, David 2009, The Emerald Planet United States, Oxford University Press

    Chadwick, Oliver et al 2013, Carbon, Fossil Fuel, and Biodiversity Mitigation with Wood and Forests, Journal of Sustainable Forestry, vol 33:3, pp248-275, 18 December 2013

    Coppens, Henry 2013, (former SAPPI technical assistant) Energy and Emissions – A positive environmental message from the forestry industry in South Africa Presentation to Saw Milling Association South Africa, 11 June 2013

    Crafford, P. L., & Wessels, C. B. (2020). South African log resource availability and potential environmental impact of timber construction. South African Journal of Science, 116(7/8). https://doi.org/10.17159/sajs.2020/6419

    Du Toit, Ben Dr. 2013, Silviculture specialist Department of Forestry and Wood Science, Stellenbosch University Personal Communication 2013

    Godsmark, Rodger 2010, Presentation: The South African Forestry and Forest Products Industry 2009 Forestry South Africa

    IPCC 2011, International Panel for Climate Change – Working Group Report 2011

    Moll, Eugene Prof. 2013, Botany Department, University of Cape Town Personal Communication 2013

    National Geographic 2011, Crimes against Nature – Chainsaw Massacre (Laos/Vietnam), National Geographic 2011

    Pacala, S. & Socolow, R. 2004, Stabilisation Wedges: Solving the climate problem for the next 50 years with current technology, Science vol. 205, pp 968-72, 13 August 2004

    Packham, 2012. BBC: The Secrets of Our Living PlanetCanadian Forests, BBC 2012

    Rypstra, Tim Prof. 2014, Wood Scientist Department of Forestry and Wood Science, Stellenbosch University Personal Communication 2014

    Stehle, Theodor 1997, The Occurrence of Indigenous Forests in South Africa: Historical and Current Forestry Western Cape Knysna, August 2007

    Tudge, Colin 2009, The Secret Life of Trees England, Penguin Books

    Walker, Gabrielle & King, Sir David 2006, The Hot Topic: How to tackle global warming and still keep the lights on London, Bloomsbury Publishing

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