Building Sustainable Skyscrapers

The population of urban areas worldwide is projected to increase by more than 2 billion in the next thirty years. Many of these individuals will require new housing. However, constructing homes using traditional materials would result in a significant release of carbon dioxide. Research conducted by the United Nations indicates that concrete, steel, glass, and bricks, commonly used in construction, contribute to approximately 9% of global CO2 emissions.

Construction professionals and architects globally are diligently seeking sustainable residential solutions that have minimal environmental impact. Mass timber has emerged as an apparent solution, leading to a notable trend in architectural practices. Mass timber, also referred to as engineered wood, is transforming the approach to building design and construction. It differs from the conventional lumber typically used in single-family homes in North America. The strength of mass timber components allows for constructing office towers or apartment blocks while emitting considerably less CO2 than standard materials. Moreover, since wood comprises about 50% carbon, the material stores a portion of it, further contributing to its environmental benefits.

This is why many companies are adopting mass timber to reduce their carbon footprints and showcase their commitment to environmental sustainability. Some notable companies such as Walmart Inc., Microsoft Corp., and Alphabet Inc.'s Google are embracing mass timber. In November, YouTube unveiled two new buildings at its San Bruno, California, headquarters constructed with timber structures, claiming that they cut emissions by half compared to a concrete-and-steel design.

However, accurately determining the amount of carbon saved by using timber in construction is not straightforward. There are significant unanswered questions, such as whether mass timber is beneficial for the climate regardless of its source and what the collective impact would be if many well-sourced wooden buildings were constructed.

Architects and engineers utilise tools to estimate the carbon footprint of timber throughout a building's entire lifespan. Specialised software enables users to conduct life-cycle assessments (LCAs) to estimate the carbon footprint of various design proposals, including the harvest, manufacturing of components, construction, and disposal stages. Designers often develop two models — one using timber and the other using concrete or steel — to compare the carbon costs better.

According to Stephanie Carlisle, a senior researcher at the University of Washington's Carbon Leadership Forum, both corporate clients and designers are apprehensive about overstating the climate benefits of mass timber. They are seeking robust systems to support their claims. Carlisle contributed to developing tallyLCA, a software tool managed by the nonprofit organisation Building Transparency, which estimates the environmental impact of building designs.

Life-cycle assessments delve into the carbon emissions generated throughout various stages of moving logs from forests to mills and further processing them into mass-timber products like cross-laminated timber (CLT) and glued laminated timber (glulam). This analysis includes the energy consumption during milling and manufacturing processes. Moreover, it considers the carbon footprint stemming from the fuel burned by construction cranes, tractors, and other machinery involved in the construction process and the emissions from renovations and routine maintenance activities spanning over decades.

The management practices employed in the forests where the wood originated play a crucial role. However, life-cycle analyses often fail to capture the advantages of sustainable forestry practices fully. To explain, let's draw an analogy. The increasing popularity of electric vehicles (EVs) has shed light on a rather obscure aspect: the environmental friendliness of an EV is influenced by the source of its electricity. For instance, a charging station powered by a coal plant contributes to emissions that renewable sources like solar energy do not. Fortunately, the power grid is gradually becoming cleaner, which, over time, will also reduce emissions from the transportation sector as EVs become more mainstream.