Sustainable materials can be used in construction to decrease environmental pollution

Efforts to reduce emissions in the building sector typically focus on operational aspects like heating and lighting. Now the attention is shifting towards the environmental impact of materials themselves. Conventional materials, e.g. cement and steel, are primarily used in construction, contributing significantly to environmental degradation. However, there are alternative materials available, such as timber, clay, straw, or hemp, which offer renewing properties. Today, each option has its own strengths and weaknesses, and questions have been raised about their true sustainability.

The OECD (Organisation for Economic Co-operation and Development) anticipates that by 2050, emissions from construction materials will compete with operational emissions, underscoring the urgency of scrutinizing material choices. Cement, steel, and aluminum alone contribute a substantial portion to global emissions, while in Europe construction activities alone emit 250 million tons of CO₂ annually.

Despite the availability of more sustainable options, such as nature-based materials, their adoption is prevented by cost considerations and industry skepticism. Nevertheless, there is a growing trend among developers and architects to incorporate these alternatives into projects. Moreover, efforts to make traditional materials greener are underway. However, the most environmentally sound approach may lie in rethinking the necessity of new construction altogether. Maximizing the use of existing buildings, repurposing materials, and extending their lifespan could offer significant emissions reductions and resource conservation benefits.

Materials like timber, bamboo, straw, or hemp have the capacity to absorb carbon during their growth. Buildings such as schools, homes, and offices constructed with these materials could potentially sequester more carbon than was emitted during their construction, effectively turning them into carbon sinks over their lifespan, which typically spans several decades.

A spokesperson from Bauhaus Earth highlighted the importance of life span and carbon storage. If the carbon stored in a 100-year-old tree remains in a building for longer than a century, it delays its release, contributing positively to atmospheric health. Furthermore, according to a 2023 report by the UNEP, a transition to properly managed bio-based materials could result in emissions savings of up to 40 percent in many regions worldwide by 2050.

However, despite these potential benefits, there are challenges preventing widespread adoption. Kim Gundlach from the Natural Building Lab underscores the lack of strong economic incentives for working with bio-based materials, particularly in countries like Germany where complex building certification processes and warranty concerns pose significant barriers, especially for reused and non-standardized products.

Sustainable materials that could reshape the future of construction and reduce carbon emissions worldwide are presented in the following lines.

Mass timber, which includes engineered wood like cross-laminated timber, has emerged as a viable competitor to steel and reinforced concrete in building structures. This sustainable construction material holds significant promise and is already widely utilized in various projects. Timber stands out as a potential ally in society's efforts to achieve climate targets, as a cubic meter of wood typically contains around one ton of carbon.

The advantages of mass timber are diverse. It boasts high durability, fire resistance, and the ability to prefabricate building components off-site in a modular or serial fashion, thereby reducing construction waste and accelerating building processes. In addition, wood's lightweight nature makes it ideal for adding stories to existing buildings, expanding living spaces without consuming additional ground area. In all, timber serves as an effective insulator, diminishing the demand for heating and cooling.

However, the environmental friendliness of wood products hinges on sustainable forest management practices and responsible harvesting, along with broader social and ecological considerations. The slow growth rate of trees and the resilience of forests to climate change significantly influence their productivity.

Clay is a widely used construction material across various regions, while it is undergoing a revival as a sustainable alternative to traditional building resources. Clay structures offer eco-friendly attributes, e.g. sound insulation, fire resistance, and local availability.

In construction, clay finds application in ceilings, walls, roofs, and floors, as well as in drywall panels and clay plasters. When formed into bricks or molded, clay (or rammed earth) exhibits impressive load-bearing capabilities.

Furthermore, it is determined that clay blocks possess a dramatically lower CO₂ footprint compared to conventional building materials like sand-lime bricks or concrete blocks, ranging from 10 to 20 times lower. Clay also exhibits remarkable temperature and moisture regulation capabilities, along with positive effects on room acoustics and climate. However, the material is susceptible to weather conditions. For instance, construction during winter may pause due to the sensitivity of clay to frost, which could compromise its properties. This requirement for specific weather conditions during construction underscores the need for different construction techniques when working with clay.

Other natural materials, such as bamboo, grasses, straw, or hemp, are increasingly being utilized to fulfill buildings' envelope and insulation requirements. These materials not only outperform many conventional options in terms of sustainability but also have the potential to enhance residents' well-being, promoting better indoor air quality.

Straw, previously considered a waste product from grains, is now being recognized as a valuable material for insulation or panels. It offers excellent heat and sound insulation properties and exhibits high resistance to moisture and mold when processed correctly. Utilizing straw as a building material typically does not necessitate additional agricultural areas.

Hemp could be used as a building material because this plant grows rapidly and requires minimal pesticide use. It serves as a viable substitute for aluminum and steel panels and is notably recognized for its application in "hempcrete", a non-load-bearing wall and insulation material. A study commissioned by the European Industrial Hemp Association (EIHA) revealed that hemp varieties cultivated in Europe can sequester between 7 and 9.6 tonnes of CO₂ equivalent per year.

Fabian Hörmann, author and founder of the regenerative YR22, emphasizes that innovation doesn't always necessitate novelty. Classic materials like earth, straw, or hemp can effectively replace carbon-intensive counterparts in certain building components. The key lies in strategically placing each material to capitalize on its specific benefits.

Considering that the EU anticipates most of its building stock to endure until 2050, the selection of insulation materials to enhance the energy efficiency of existing structures becomes imperative for achieving climate neutrality. Natural insulation materials, such as cellulose or regionally sourced options like flax, cork, reed, and paludicultural crops, are not initially inferior to synthetic alternatives.

Low-carbon cements can stand as an alternative material as cement and concrete dominate Europe's building landscape, constituting approximately 70 percent of the total mass of buildings. Cement ranks as the second most used material globally, following water.

Despite its remarkable qualities, the production of cement, especially Portland cement, is intrinsically polluting. The conversion of limestone, its primary component comprising around 90 percent, into clinker releases significant carbon emissions (750-850 kg per tonne of cement). As a result, 6-8% of global emissions are attributed to the cement industry, surpassing the emissions from global aviation.

Regardless of these challenges, efforts to reduce the carbon footprint of cement are underway. Strategies include altering concrete production materials, redesigning structures to use less cement (such as a University of Stuttgart project that developed concrete with pores or cavities in low-load areas, saving up to 40 percent of material), and promoting the reuse of existing components.

However, challenges remain, including cost escalations (current production costs increase by 50% to 85%) and the lack of infrastructure for carbon transport and storage. The transition to more sustainable cements faces obstacles due to the considerable capital invested in existing infrastructure for traditional Portland cement production.

Madeline Rihner, a Sheffield University PhD researcher, emphasizes that there is no single solution to decarbonize the sector. Instead, a combination of strategies will be necessary, depending on the application. With global demand for cement and steel projected to rise as populations and urbanization increase, the focus is not on replacing cement and concrete but on making them more environmentally friendly and sustainable.