Column | The tricky business of sustainable materials

Building stones. Photo: Ann Rochyne Thomas

The inefficient production and unsustainable consumption patterns of contemporary society necessitate radical changes in the way we design, construct, and de-construct our built environments. The construction industry is responsible for nearly 60% of natural resource extraction and 38% of total global carbon emissions.

Until recently, the deciding factors in construction material selection were cost and aesthetics; environmental impacts were more of an afterthought. The knowledge of environmental issues has increased people's awareness of the linkage between building materials, energy requirements and environmental impacts. However, the widespread adoption of sustainable building materials and techniques has been hampered by the misconception that energy-efficient buildings are cost-intensive.

Assessing a material’s ‘fit’ in the sustainability puzzle

In sustainable construction, resource efficiency, ecosystem integrity and adequate thermal comfort do not come at the expense of cost-effectiveness and aesthetics. Operational energy, or the energy required over a structure's entire service life, can make up a sizable fraction of the total energy utilised by it. The embodied energy of a material, which is the energy used in operations from extraction to installation and maintenance, may range from 4% to 52% for those used in conventional buildings, while it can range from 18% to 77% for those used in passive buildings. Often, a reduction in the operational energy demand of a building is at the cost of using energy-intensive walling materials for the building envelope, that possess high insulating capacity as well as high embodied energy. Buildings with low embodied energy materials may require more operational energy to run it. Focusing solely on energy efficiency and carbon footprint may cause people to overlook other factors such as habitat destruction, biodiversity loss and multiple types of environmental pollution from mining and processing.

To prevent such counterbalances, materials must be chosen with consideration for both their structural performance, resource efficiency and environmental impact. Responsible sourcing and lifecycle analysis (LCA) can determine the potential cradle-to-grave environmental impact of building materials. A material that is fit to accommodate future climate change impacts, can prolong its service life and significantly reduce the need for upgrades. The end-of-life management of materials can also have a significant effect on the overall environmental impact of a structure. Designing for de-construction or disassembly with a cradle-to-cradle approach can transform the building process, to enable material re-usability in its original form or recyclability with minimal waste to help recover embodied energy.

How sustainable are laterite bricks as a building material?

Tropical regions in Asia have historically used traditional walling materials like laterite, a residual ferruginous rock formed under intense and long-term humid tropical weathering. Laterite walls have a distinctive appearance due to the earthy red and yellow ochre hues of the iron-rich laterites and the rough texture with pores and cavities resulting from leaching. Laterite may be easily cut in-situ into homogeneous blocks when newly quarried. The bricks progressively harden upon exposure to air. Laterite can also be used to produce high-density interlocking bricks without cement mortar. Due to their larger size than conventional bricks, fewer of them are required for building walls, decreasing installation time. Laterite walls have high fire resistance capacity, provide thermal comfort and sound insulation, and offer a rustic appearance, making plastering and painting optional. Additionally, laterite beautifully complements ‘Parambu’ – Kerala’s traditional homestead forests. All these factors, together with the availability of a skilled labour force competent to work with these locally abundant laterite rocks, resulted in it becoming a popular building material in several regions of Kerala. As it requires less energy for its extraction and processing and has high thermal efficiency, this non-renewable resource is considered as a sustainable building material.

The location of the quarry, the depth of the laterite, the type of weathered rock bedding, and the amount of iron present, all affect the laterite rock's properties. Compressive strength of laterite rocks has been observed to decrease with depth in a quarry, while water absorption capacity has been found to increase.

Laterite rock was first documented in 1807 by Dr. Francis Buchanan-Hamilton in Angadipuram in the Malappuram district of Kerala. ‘Angadipuram Laterite’ is a national geo-heritage monument that celebrates this rock that has been used as a building stone for over 1000 years. Laterite bricks are less popular among contemporary architects and homeowners because they are incompatible with many modern building practices. Laterite bricks are five to ten times weaker than concrete bricks, limiting laterite masonry load-bearing structures to double or triple storeys. Laterite structures cannot be reinforced with steel and are therefore less earthquake-resistant than concrete structures. Because of their moisture retention capability, they are less ideal for regions with heavy rainfall. For usage as building stones, they must have high compressive strength and low water absorption capacity. Such good-quality rocks can be found near the top of laterite profiles. In recent years, the removal of topsoil and quarrying of laterite hills, and its devastating effects on biodiversity, have pushed many to question laterite's status as a sustainable material. Rotala malabarica (Malabar rotala) is a short-lived annual plant found in a single location on the Madayippara Laterite Hills in the district of Kannur in Kerala. This endemic species has a restricted range of approximately 10 square kilometres and is critically endangered. They inhabit what is locally called ‘pallam’ - seasonal pools on laterite substrates, with rich humus deposits. For the region's water supply and quality to remain stable, these laterite hill ecosystems are essential. Biodiversity reduction and loss of integrity of water resources caused by laterite mining, such as in Madayippara, are rarely discussed, let alone addressed.

Only through responsible sourcing and efficient utilization can laterite be a viable alternative to meeting the growing need for new infrastructure in regions of tropical Asia. The demand for construction materials can be reduced only by shifting away from enormous residences and multiple dwellings that are infrequently occupied. Furthermore, open floor plans will reduce the need for materials for interior walls. The demand for raw materials will also decline if boundary walls are replaced with living walls and pavements with exposed soil and vegetation.

A delicate balance

Sustainable construction necessitates efficient designs that utilise fewer finite resources, the utilisation of a diverse variety of local building materials, and the incorporation of a closed-loop material cycle (CLMC). Building energy efficiency solutions have the potential to significantly cut greenhouse gas (GHG) emissions in the short and long run. For true environmental stewardship, it is critical to avoid a carbon tunnel vision and instead focus on the larger picture. Sustainable construction policies must ensure that the rise of net-zero buildings does not come at the price of irreversible damage to ecosystems. A worldwide sustainable materials database with environmental profiles and standardised testing methodologies, accessible to a wide variety of stakeholders, would help in the informed use of laterite and other construction materials.

(Ann Rochyne Thomas is a bio-climatic spatial planner and founder of Centre for Climate Resilience - a sustainability and climate change advisory.)

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