How can we protect our homes from extreme rainfall?

In September 2023, a new research project was launched to identify the most economically and environmentally sustainable measures for climate-proofing homes. The project was led by CICERO (Center for International Climate Research) in collaboration with IVL (Swedish Environmental Research Institute), and was funded by If and SIVL (Swedish Institute for Water and Air Pollution Research). In addition to funding, If contributed with claims data and insights into how flooding and leakage most commonly occur.  

The goal has been to identify concrete climate adaptation measures that are feasible for individuals and housing associations while also being sustainable from a climate perspective.  

• Installing a backflow valve to prevent sewage water from backing up into the home. 
• Early replacement of drainage systems to reduce the risk of water intrusion. 
• Redirecting downspouts to a rain garden via a shallow trench. 
• Redirecting downspouts to stormwater infiltration crates via underground pipes.  

Using life cycle analyses (LCA) and cost-benefit analyses (CBA), researchers have examined both the climate impact and the economic consequences of each measure. The results show that several of the measures can be highly effective, particularly in areas where extreme rainfall is recurrent.  

For example, a backflow valve can significantly reduce the emissions associated with a property compared to the emissions generated by remediation after water damage. Other measures, such as redirecting water to a rain garden, provide benefits not only for the homeowner but also for surrounding properties, which raises questions about how to create incentives for property owners. The results vary depending on how frequently damage occurs, which highlights the importance of adapting measures to local conditions and risk levels. 

“Our analysis shows that the backflow valve is the measure that is most likely to reduce both costs and emissions. Rain gardens stand out as a sustainable measure for preventing water intrusion, and with conservative estimates of carbon sequestration, rain gardens perform even better in life cycle analyses. At the same time, we see that stormwater infiltration crates perform less well, as they are both more expensive and more emission-intensive than rain gardens. Accelerating investments in new drainage systems is costly and emission-intensive, and can therefore hardly be considered a sustainable measure”, explains Sofie Skjeflo, who is a senior researcher at CICERO.  

In the research, sustainable measures are defined as those that do not increase greenhouse gas emissions over their lifetime compared to simply repairing damage. At the same time, they must be economically viable.  

“We are continuously working to develop our damage prevention efforts to better support our customers. Preventive measures can reduce the risk of damage and result in both lower financial costs and reduced environmental impact. The results of this research project are valuable for increasing knowledge about the climate adaptation of buildings. They help us to further develop our preventive work while also strengthening society’s resilience”, explains Philip Thörn, who is Head of Sustainability at If. 

The study highlights that preventing damage from extreme rainfall and stormwater must be assessed beyond the boundaries of an individual property, according to CICERO.  

“Nature-based solutions such as rain gardens can provide benefits for the surrounding environment, including reduced water pollution, increased biodiversity and aesthetic value. These results underscore the need for incentives that can promote investments in sustainable preventive measures, both for households and at the municipal level”, says Sofie Skjeflo.  

As part of the project, If provided claims data from real events, which made it possible to link the results to actual costs and climate impact. This research is an example of how If actively works to contribute to a more climate-resilient society. By identifying effective measures and spreading knowledge, we help to protect society from the increasing risks posed by climate change. 

The full report is available here.