While many cities are pursuing urban densification strategies in an effort to lower urban emissions, a new study finds that cities will have a greater impact in the fight against climate change if they focus on energy-efficient construction.

“You can do a lot of things at the local level to affect housing stock that are basically equivalent or even more aggressive than the Clean Power Plan,” said David Hsu from MIT, one of the three co-authors of a new paper detailing the study’s findings. The Obama administration introduced the Clean Power Plan in 2015, but the Trump administration has announced that it intends to repeal it.

Some residential energy use strategies will have a great impact over others, finds the study. For instance, requiring newly built homes to be more energy efficient would reduce residential emissions by an average of 6 per cent by 2030. But requiring existing homes to be retrofitted would yield a further 19 per cent reduction of residential emission, on average, across the 11 cities analysed in the study.

Perhaps surprisingly, there was relatively less benefit in reducing the number of newly built single-family homes and replacing them with multi-family buildings. 

“Shifting people to multifamily buildings is what planners have always wanted to do, but that’s actually not as effective as most advocates would have thought,” Hsu said. 

The main reason is that as new homes become more energy-efficient, the energy-use differences between larger single-family homes and homes in multi-family dwellings will shrink, thus “reducing the energy and emissions benefits of any substituting attached homes for detached ones”.