Pre-20th Century Construction Practices May Offer Clues to Tackling Climate Change

The common assumption about technological advancement is that it always moves forward, but sometimes, taking a few steps back is necessary for progress. This is a common theme conveyed by the most recent report by the United Nations Environment Program entitled “Building Materials and the Climate: Constructing a New Future.”

With a history of more than five decades, UNEP describes itself as “the leading global authority on the environment,” working closely with the public and private sectors—including the UN’s 193 member states—to promote solutions to the triple threat of global warming, pollution, and biodiversity loss. The organization is an excellent source of information about environmentally responsible building materials and construction practices, as evidenced by this report.

Released in September 2023, “Building Materials and the Climate” consolidates multiple sustainable material themes into one document with clear and assertive recommendations for how the built environment must address climate change. The report summarizes what many in the industry have been discussing—that although operational energy (HVAC, lighting) has been the primary focus, embodied energy (material design, fabrication, and installation) is equally, if not more, impactful—with robust new data to support this claim.

The publication offers three primary strategies to decarbonize buildings and infrastructure: avoid, shift, and improve—a more holistic update to the familiar “reduce, reuse, and recycle” wisdom. Each pathway offers an opportunity to reflect and recalibrate, articulating solutions based on an appreciation for pre-industrial approaches that were less ecologically destructive than contemporary ones. In this way, the report’s authors outline how progress must include resurrecting past knowledge in combination with today’s technological expertise.

The first method, avoid, advocates eliminating the extraction and generation of raw materials. Yes, you read that correctly: an argument against using virgin materials. This pathway is based on the environmentally advantageous practices of both preindustrial and informal communities, in which circular economy principles have delivered a significantly lighter resource footprint. Recommended strategies include extending buildings’ lives through reuse and designing structures for disassembly instead of demolition.

Notably, the authors denounce modern reinforced concrete. In a condemnation of the problematic properties of this ubiquitous material, whose untreated steel poses an imminent threat to durability and safety, the report’s authors charge developed economies with “repurposing the massive quantities of failing reinforced concrete from 20th-century infrastructure that is nearing the end of its first life, so that it can be transformed into material ‘banks’ for new construction to slow the pace of non-renewable material extraction.” This notion of treating existing structures as material stores for future building—a circular economy tactic seen more prevalently in pre-20th century societies—appears repeatedly in the publication.

The second strategy, shift, involves the deliberate transition from non-renewable to renewable resources. “The shift toward properly managed bio-based materials could lead to compounded emission savings in the sector of up to 40% by 2050 in many regions,” the authors write. This pathway promotes bioproducts, which—because they are renewable and absorb atmospheric carbon—offer measurable benefits compared to non-renewable resources. However, this is just a start. The report further envisions the architecture, engineering, and construction industry joining the forestry and agricultural sectors to “lead a revolution in the carbon cycle management of regional ecosystems.”

By directing the attention of world leaders, government agencies, businesses, and civil society to the problem of embodied carbon in building materials, UNEP is increasing public awareness of this issue and laying the groundwork for the highly coordinated and interdisciplinary efforts ahead.

The authors point out that pre-20th century construction was primarily bio- and earth-based and thus exhibited a much lower ecological footprint than today’s fossil fuel-driven, mineral-based construction palette, including concrete and steel. Surprisingly, many contemporary structures made from these non-renewable materials are less durable than their pre-20th century counterparts. By shifting the emphasis away from mineral resources to materials like timber, bamboo, and non-timber lignocellulosic materials (biomass), it will be possible to harness “technology to improve materials while recapturing the intelligence of the past,” according to the report. Such techniques include advancing green chemistry to develop non-toxic glues and binders for bio-based products.

The third tactic, improve, aims to enhance contemporary building materials and practices. It’s no surprise that cement, steel, and aluminum are the three most significant sources of embodied carbon in the construction industry—or that concrete, steel, and aluminum contribute 23% of total global emissions, according to the report. Therefore, process improvements that reduce the carbon footprint of these and other nonrenewable materials can make a measurable difference. According to the report, the use of concrete and steel has increased by factors of 10 and 3 in the past 65 years, respectively, compared with a negligible increase in the use of timber.

Electrifying the production process (replacing blast furnaces, for example), extending building lifespans (as mentioned above), and increasing material recycling rates are among the critical strategies for improving these materials’ environmental performance. The report emphasizes the pre-modern and informal practices of repurposing waste building materials in new applications as examples to emulate. “These methods are already widespread in informal and semi-formal housing throughout the world, and much could be learned from those practices for the formal sector as well,” the authors state.

Given its critiques of contemporary design, specification, and construction, “Building Materials and the Climate” might initially seem to be promoting a regressive narrative. But this is not the case. The authors are making an informed argument, supported by a robust set of recent scientific studies, that further societal progress will require a change in our current material practices, systems, and policies—a change that should include the consideration of pre-modern and informal approaches.

“Building Materials and the Climate” is not the typical polite sustainable design guideline with the “every little bit counts” message. The report pulls no punches, exposing the deep-rooted, intrinsic problems in today’s most common construction materials and methods. And yet, this is just the medicine we need, and it could direct new and welcome avenues of support. “The built environment sector is by far the largest emitter of greenhouse gases, responsible for at least 37% of the global emissions,” the authors write. “Yet it has received only a small fraction of climate-focused development funding, compared to other sectors.” By directing the attention of world leaders, government agencies, businesses, and civil society to the problem of embodied carbon in building materials, UNEP is increasing public awareness of this issue and laying the groundwork for the highly coordinated and interdisciplinary efforts ahead.

The views and conclusions from this author are not necessarily those of ARCHITECT magazine or of The American Institute of Architects.

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