An EPFL study measured the carbon footprint of 20'000 residential buildings in Vaud Canton. The authors' findings show that a targeted approach will be key to lowering the emissions associated with residential real estate.
Decarbonizing the real-estate sector is a huge challenge, and one that Ankita Singhvi has set out to tackle with her PhD research at EPFL. "I want to help policymakers and property developers with large portfolios determine what their priorities should be in terms of renovation projects," she says.
Singhvi, who holds degrees in architecture and industrial ecology, is currently a PhD student at EPFL's Human-Environment Relations in Urban Systems (HERUS) Laboratory. Part of her research has just been published in Resources, Conservation & Recycling. Looking specifically at Vaud Canton, she used data from buildings' energy audits to calculate their carbon emissions, including both their operational emissions (from heating and electricity, for example) and embodied emissions (from the entire construction process). She also factored in the number of people living in each house or apartment in order to calculate the average annual carbon emissions per resident.
Given the aging population, we can expect to see more and more rural households with just one or two retired people in homes in need of energy.
Differences between urban and rural areas
The study, which covered 15% of all residential buildings in the canton (20'000 buildings in total), found that urban households have lower embodied emissions than households in rural areas: the area per capita is often larger outside cities and there are more diverse mixes of old and new buildings. In cities, 70% of housing was built before 1980.
But operational emissions are generally higher in urban areas, ranging from 1,500 to 1,900 kg of CO₂ per resident per year, owing to outdated fossil-fuel based heating systems. Rural households showed greater overall variation in their annual carbon emissions, which ranged from 1,200 to 2,200 kg of CO₂ per resident. The researchers attribute this to the relatively higher per capita surface area, more variability in construction periods (22 % modern buildings constructed post-2000, and 34% very old pre-1920 buildings) and the higher adoption of technologies such as photovoltaic panels (compared to urban areas) for energy generation which reduces the CO2 emissions per resident.
The studies show that the carbon footprint of rural areas could increase in the future, says Singhvi: "Given the aging population, we can expect to see more and more rural households with just one or two retired people in homes in need of energy efficient renovations, like low-carbon heating systems and better insulation," says Singhvi.
The study also showed that mixed-ownership buildings had the highest embodied energy, the largest stock of materials and the most modern buildings, while community-owned buildings showed the widest variation in annual operational emissions, ranging from 1,500 to 2,300 kg of CO₂ per resident.
Case-by-case approach
"Our study identified the diversity of measures needed to improve the environmental performance of Vaud's building stock," says Singhvi. She and her colleagues hope their findings will discourage the use of one-size-fits-all strategies that miss the target. Singhvi points out that one way to shrink the sector's carbon footprint is to select the right renovation materials. She gives the example of reuse: every time a building is demolished, that can be an opportunity to source materials for renovation work on neighboring buildings. This extends the life of construction materials by giving them new functions.
In their conclusion, the researchers stress that not all renovation projects lead to reductions in operational and embodied emissions. Projects designed to improve a building's envelope or update its heating and cooling system, for example, may result in lower operational emissions, but they could also encourage residents' energy-consuming habits. Hence the authors suggest analyzing properties on a case-by-case basis, and taking household practices into account as well as the technical specifications of the building.
There are still a number of legal and administrative hurdles preventing people from exploring different types of living arrangements.
More creative solutions
When it comes to lowering the carbon emissions of buildings in Vaud while addressing growing housing needs, one option could be to set up temporary arrangements, such as by offering student rooms to rent in large homes where only one or two people currently live. "There are still a number of legal and administrative hurdles preventing people from exploring different types of living arrangements," says Singhvi. "I hope our research will help policymakers and property developers become more creative."
Singhvi's research will be taken further with data from the Lake Geneva Sustainability Monitoring Panel, a five-year study being carried out by EPFL's School of Architecture, Civil and Environmental Engineering (ENAC). Researchers will survey a representative sample of Lake Geneva residents on their attitudes and behaviors towards the environment, with a view to proposing concrete measures aimed at limiting people's environmental impact. Data on Vaud residents' commuting habits collected in the survey will be factored into the overall carbon emission calculation in order to obtain a more complete picture.
As a point of comparison, the '2000W-society' envisions an average annual housing-related energy use of 3900 kWh per resident. Single-person households are the fastest-growing demographic in Switzerland. For researcher Ankita Singhvi, these households therefore present a key opportunity for technical and social housing innovations in order to achieve the climate goals set for 2050.
