Carbon sink and low-carbon building materials

Materials and products used in building, such as steel and aluminum, are created by a production process of raw material extraction, raw material process, melting, manufacture to final products, and transportation to building sites. Each of the steps consumes energy, which is also expressed in terms of carbon emissions. Total carbon emissions of all building materials and products and the construction involved to put them together is known as building’s embodied carbon. Embodied carbon accounts for about 20% of the carbon emissions from the building sector (Lane, 2010).

Introduction carbon sink and low-carbon building materials

Reducing embodied carbon is one of the simple and practical mitigation options for the building sector by utilising carbon sink and low carbon materials and products in buildings. Carbon sink building materials are mainly sourced from harvested wood products (HWPs). Wood is harvested from trees that capture carbon through the process of photosynthesis. Fifty per cent of the dry weight of wood is carbon, and the amount of carbon in 1m3 of wood is similar to that in about 350 litres of gasoline (Labbe, 2010). It is important to ensure that the wood comes from sustainably managed plantations. Wood from illegal forest logging is not carbon-neutral and should not be used at all. Illegal logging permanently destroys vast natural carbon sinks and their associated biodiversity, which can not be easily restored. Using non-sustainable source harvest wood products is more environmentally detrimental than the benefits of using low-carbon materials in buildings.

Not all building materials can be carbon-sinks. In such cases, low-carbon building materials should be used as much as possible. Low-carbon building materials can be sourced from materials with both low embodied energy and carbon in their production, assembly, and transportation processes. Due to the broad-based definition, low-carbon building materials are interpreted differently in different contexts. For example, metal products are considered to be high-embodied carbon materials because the extraction and refinement processes involved are carbon intensive. However, recycled metal products used in new buildings can be considered low-carbon.

Carbon sink building materials and products

The harvested wood building materials and products include flooring and cladding materials, window frames, doors, furniture, structural columns, beams and rafters. Bamboo products have recently received a lot of attention, due to its fast-growth, renewability and availability in both tropical and subtropical climates. Laminated bamboo has been found to be tougher than soft steel, and the surface is harder than that of red oak timber and fibreglass. Consequently, bamboos have been widely used in building structures, screen walls and as roofing components. Bamboo products have also found application in the high-end building market, for example, treated bamboo flooring.

 

Figure 1: Application of carbon-sink materials in buildings.

Low carbon building materials and products

Low carbon building materials and products have been the subject of research and development. This has resulted in many innovative building material products through the use of by-products and recycled products. Some examples of recently developed low-carbon materials and products in the market include:

1. Low-carbon bricks. These have been rolled out for mass production and implementation since 2009. The use of 40% fly ash (Ritch, 2009) helps to reduce embodied carbon found in conventional bricks. Fly ash is a fine glass powder that consists primarily of silica, iron and alumina. It is a byproduct of coal combustion from electricity generation and is disposed of after being separated from the flue gas.
2. Green concrete. The raw materials to form conventional concrete can be substituted with byproducts of industrial processes and recycled materials. For example, carbon intensive Portland cement can be substituted by fly ash and granulated blast-furnace slag. Aggregate or sand can be substituted by washed copper slag, and granite by recycled granite from demolished debris.
3. Green tiles. These are ceramic material made from over 55% recycled glass and other minerals. The products turn waste glass into tiles for use in building’s internal and external flooring and cladding. The sparkling recycled glass components add an aesthetic quality to the products.
4. Recycled metals. The production process of metal products is highly carbon intensive. However, the life cycle performance of metal products can significantly reduce their production energy consumption, for example, by 95% for aluminium, 80% for lead, 75% for zinc and 70% for copper. This is because repeatedly recycled metals can still maintain their properties (Stewart et al., 2000). Other forms of utilising metal products without the full recycling process (which includes re-melting the old metal products and re-moulding them into new products) is to reuse existing metal structural components, such as steel columns and beams that still maintain their structural performance. Lastly, building-unrelated metal products, such as shipping containers, can also be adaptively reused in new building projects.

In addition to the examples above, there are many other innovative low carbon products available and many more are undergoing research and development.

 

Figure 2: Shipping containers can be adaptively reused in new buildings.

Feasibility and operational necessities of carbon sink and low-carbon building materials

The vast opportunities for application of carbon-sinks and low-carbon materials and products can be identified in many building types and locations. On one hand, technical requirements for most of these materials are similar to any other ordinary materials used in buildings. For instance, harvested wood products, similar to the application of any conventional wood products in building, should be resistant to termite infestation and moisture damage. Technology-enhanced wood products, such as, involving lamination and chemical treatment, can reduce their vulnerability to termite infestation, and strengthen their water- and humidity-resistance.

 

Figure 3: Examples of timber construction detail.

On the other hand, strict requirements do apply to the use of certain carbon-sink and low-carbon materials and products for safety and environmental health reasons.

The good intention of using carbon-sink and low-carbon materials may not achieve their optimal effect, if these materials are wasted during application. Materials are often wasted in order to achieve a certain perceived aesthetic effects. As a result, standardised modular materials are often trimmed off and cut at the construction site to meet the design intent, and the remaining materials become waste. Therefore, minimising waste by taking into account the standard sizes of building materials is a prerequisite in lowcarbon building design practice.

The feasibility for implementation of carbon-sink and low-carbon building materials and products is high. It is often dependent on architects’ willingness to design and specify such products, and on building developers’ acceptance. It also hinges on the local availability of the products. Four key success factors that facilitate such actions include:

1. General awareness, which can be built through public education campaigns, professional development programmes for building and construction professionals and developers, and supported by demonstration projects.
2. Local availability of the materials and products. An enabling mechanism is important to create the market and facilitate the development of the local building material industry. These materials and products should also be constantly upgraded to be technologically sound and cost effective.
3. Institutional support plays an important role in fostering the recognition, development, and implementation of carbon-sink and low-carbon building materials and products. One of the most effective tools is green labelling and carbon labelling schemes coupled with certification programs for building materials and products. These labelling schemes can be set up by government agencies or reputable NGOs.
4. Capacity building is a useful way of updating local professional and technical work forces about existing and new carbon-sink and low-carbon building materials and products.
5. Research and development. One of the most effective forms of collaboration are targeted research and development programs between universities, industry and government agencies. The objectives are to identify and develop new potential carbon-sink materials and products, and their innovative applications.

Status of the technology and its future market potential

To mitigate climate change impacts from the building sector, low-carbon and especially carbon-sink materials and products have been considered as one of the most important mitigation opportunities. Many regional and national governments have established green building product labelling systems and carbon labelling systems, which further foster the implementation and market penetration of these materials and products. Examples of these systems are Taiwan’s Green Building Material Label and Singapore’s Green Building Products. These systems certify products, based on a number of environmental aspects, including low-carbon intensiveness, local materials, environmental health hazard, etc. Dedicated carbon labelling schemes for building materials and products is an emerging practice. However, it is currently grouped under carbon labelling systems, which cover all product categories – such as food and beverage products, cleaning products, etc. Examples of carbon labelling systems include Carbon Trust’s Carbon Footprint, South Korea’s Low Carbon Product Certificate and Thailand’s Carbon Reduction Label.

Among carbon-sink products, bamboo has recently been recognised to have high potential. As the demand for harvested wood products increases, bamboo is used as a substitute for slower-growing wood species with high commercial potential. In 2007, bamboo represented 4-7% of the total tropical and subtropical timber trade (Lou et al., 2010).

Furthermore, innovative applications result in a wide range of bamboo products that are even recognised by many national building codes. For example, Colombia recognises the earthquake-resistant designs and construction methods involving bamboo in the nation’s building code. Due to bamboo’s widespread availability in developing countries, harvested bamboo products have strong market penetration potential and South-South transfer opportunities.

How carbon sink and low-carbon building materials contribute to developing countries socio-economic development and environmental protection

Carbon-sink and low-carbon building materials and products offer a key mitigation option from the building sector while contributing to social and economic development, especially in developing countries.

Carbon sink and low carbon materials substitute conventional carbon intensive materials and reduce their demand. Buildings last for a long time, sustainable harvested wood products used in buildings offer alongterm preservation and a sink for the carbon absorbed in the wood products. When stringent regulations are put in place for sources of harvested wood products, the demand for sustainably managed forests will increase,which in turn creates a stable source for legal HWPs. As a result, more carbon can be absorbed from the atmosphere and more green jobs can be created, in both the building and forestry sectors, contributing to the green economy.

 

Figure 4: Estimated carbon emission savings from substituting one cubic metre of timber for various building components (source: Ruter, 2011)

The widespread use of low-carbon building materials and products also promotes local environmental and socio-economic development. The use of locally available materials and products not only reduces the use of carbon intensive materials, but also reduces the embodied-carbon from long distance transportation. This also supports the development of local industries, which in turn provide jobs for local residents. Moreover, the increasing use of recyclable materials and industrial waste by-products reduces the need for waste treatment and disposal, reduce natural resource extractions and the energy required. This will also create an economy of scale to reduce the cost of recycled-content material production; increase the demand for the materials, which in turn help create a positive feedback loop; and make the use of lowcarbon materials and products a mainstream practice.

Financial requirements and costs

Because building materials and products are necessary to create a building, the financial requirements are less of an issue compared to that of other mitigation technologies. True carbon-sink and low-carbon materials and products should not incur an additional investment requirement. Their cost can potentially be even lower than carbon-intensive products, due to local availability that saves on transportation costs, and lower ingredient costs due to recycled or by-product materials that are substituted for virgin raw materials. Furthermore, many wood materials and products are conventionally used in buildings for a long time before the awareness of climate change. Therefore, the use of harvested wood products is not considered to incur additional investment cost.

References

• Labbe S. (2010). Influence of Material Use in Green Building Policies (A Convenient Truth). Presentation at UNECE Timber Committee Market Discussions and Policy Forum. 11-14 Oct 2010.[Online]: [[1]]
• Lane T. (4 June 2010). Embodied energy: The next big carbon challenge. Building.co.uk. [Online]: [[2]]
• Lou Y.P., Li Y.X., Kathleen B., Giles H. & Zhou G. (2010). Bamboo and Climate Change Mitigation. Beijing: International Network for Bamboo and Rattan.
• Ritch E. (27, Oct. 2009). CalStar gives sneak peek of low-carbon brick factory. Cleantech Group LLC. [Online]: [[3]]
• Ruter S. (2010).Consideration of Wood Products in Climate Policies and its Linkage to Sustainable Building Assessment Schemes. In Proceedings of the International Convention of Society of Wood Science and Technology and United Nations Economic Commission for Europe – Timber Committee, October 11-14, 2010, Geneva, Switzerland.
• Stewart D.L., Daley J.C. & Stephens R.L. (Eds.) (2000). The Importance of Recycling to the Environmental Profile of Metal Products. Pittsburgh: The Mineral, Metals & Materials Society.