Does modern construction mean more or less emissions?

In recent years, modern methods of construction (MMC) have been hailed as a solution to a variety of issues facing the sector, including but not limited to housing shortages, skills gaps and climate change.

MMC, due to its reputation for efficiency and reduced waste, is often assumed to have a lower carbon footprint by default. But is this actually the case in practice?

Last year my colleagues and I published a study entitled Understanding the embodied carbon credentials of modern methods of construction, which attempted to establish whether adopting MMC resulted in embodied carbon reductions.

The research was intended to test an increasingly dogmatic perception in the construction industry that this was indeed the case, upheld by a shaky and fragmented evidence base with a range of conclusions.

After completing the review and analysis of the existing literature, the answer was ultimately unclear.

While we concluded that the evidence of embodied carbon savings simply by adopting MMC was not robust, the research nonetheless raised a number of important and interesting follow up questions.  

After eliminating irrelevant papers – for example, articles that used MMC to refer to a different process or field – the remaining studies were filtered for data quality before a third stage captured articles missing from the first search.

The final result was a sample of 41 articles that compared traditional construction methods with MMC, or 82 case study comparisons.

Examining these 41 papers, we quickly found that there was no consistency in methodology or language used from paper to paper, region to region, or method to method.

Because of the differences in the methods used by each research team conducting the studies, we couldn't compare absolute figures across papers, but we could compare the differences within studies.

We found that the construction methods being compared were so wide-ranging that the individual conclusions from any one study could not robustly scale to signify broad conclusions either for or against MMC (Figure 1). Rather, all buildings and options need to be assessed on a case-by-case basis.

Instead of then viewing MMC as a specific process, we conceptualised it as a spectrum, with vernacular and other labour-intensive architecture on one end and fully fitted modular on the other end (Figure 2).

In an attempt to make a precise comparison, some researchers assessed in the study sought to quantify the percentage of MMC adopted.

Our findings reiterated that buildings do not fit into a simple binary of MMC or not MMC. They are a mix of materials and components that derive from various methods.

In one example, a study compared a very country-specific construction methodology with that of something more traditional. The researchers reported a significant result in the local context and concluded that this finding had global relevance for prefabricated construction generally.

The speculation present in many of these papers is perhaps the most important observation in our analysis. 

It creates a risk that a peer-reviewed study with poorly thought out conclusions could be cited in policy recommendations to justify something that is neither rigorous nor representative.

This becomes increasingly problematic with the increased use of AI and its current inability to discern credibility in research. 

The job of a researcher has evolved and now requires a particularly sharp detective lens when reading.

For example, one study found that modular timber construction uses more material, a perfectly fine conclusion to make that was based on a transparent methodology.

However, the researchers then erroneously concluded that because more timber material was used – and because timber stores carbon – the modular solution represented a more positive environmental outcome in all cases, despite a lack of evidence to support this.

Another study comparing on-site with off-site methods assumed zero waste in the off-site scenario which, if even possible, would be very rare.

In a different study, we found on interrogation that in the two scenarios being compared, a favourable assumption was made for the modern steel case and an unfavourable assumption was made for the 'traditional' concrete base case.

However, it is also possible to reduce waste through better quality control that factories can achieve compared to on-site construction.

In summary, there are benefits to both construction typologies, so designers and specifiers should consider both solutions and evaluate their credentials on a case-by-case basis.

Additionally, embodied carbon measurement is only one factor that we need to consider when striving for a sustainable long-lasting built environment.

There are many other, much more difficult-to-measure variables to consider such as the building's structural robustness, its perceived value to the public, and its ability to adapt to the fast-moving needs of the location where it has been placed.