The Triple-Bottom-Line Impacts of Choosing Modular, Part 4: Environmental Impact

Geared to the needs of nonprofit owners and developers of affordable multifamily housing, this is the fourth in a series of posts addressing the financial, social, and environmental impacts of making the shift from onsite to off-site construction.

How green is modular construction, when it comes to multifamily housing?

Usually, when we talk about green building, we focus on the physical properties of the end product—its sustainably harvested lumber, triple-pane windows, low-flow water fixtures, LED lights, and solar panels. In short, we look at a building’s materials, systems, and design features and ask how they impact the building’s carbon footprint and resource use throughout its life.

From this perspective, there are few inherent differences between modular and conventional buildings. With both models, some builders are greener than others, and most can deliver buildings to a wide variety of green standards based on the needs of their clients. Still, modular buildings do outperform conventional buildings by one green-design metric: they tend to be more stoutly built and therefore are more durable than their site-built counterparts. (See Part 3 of this series for more information on how the quality and longevity of modular buildings compares to that of stick buildings.)

With modular construction, simple, repetitive designs contribute to significant reductions in construction waste.

To more fully compare the environmental impacts of modular and onsite construction, though, you’d want to look at the manufacturing process, too. In other words, you’d ask which process is more efficient when all the energy used to produce an average building is considered.

That’s an important question, because the two manufacturing processes differ profoundly in one respect: one is centralized, the other decentralized. This difference creates distinct energy-use patterns related to the transport of materials, equipment, workers, and (in the case of modular construction) completed modules to and from construction sites and/or plants. Unfortunately, how these transport patterns impact energy use in the production of a given unit of housing remains unclear; research I’ve found on this topic is limited and inconclusive.

Still, a critical literature review published by University of British Columbia researchers in 2016 found that modular building measured higher for life-cycle sustainability, inclusive of the manufacturing process, compared to conventional building—a finding tied in part to another significant area of environmental impact: production of material waste.

Modular construction’s relatively efficient production process results in less scrap material compared to conventional construction. What scrap there is can be kept and reused on subsequent projects. The waste differential is substantial: using modular construction to produce high-rise structures cut construction waste on those projects by at least half, more than offsetting the extra materials required to beef up the buildings’ modules for transport, according to a 2012 study.

Conclusion: Owing to a lack of data it’s not clear that either model, modular or conventional, is greener than the other. But going by standard metrics and available evidence, modular construction racks up more green points, based on its lower rate of manufacturing waste and the superior durability of its finished product.