As the city prepares for London Climate Action Week 2026, the conversation must increasingly focus not only on cutting emissions, but on adapting to the risks already being felt by communities, businesses and infrastructure. Flooding is one of the clearest examples of why this matters. More intense rainfall, growing pressure on drainage systems and a housing shortage means surface water flood risk is becoming a practical challenge for development, investment and long-term resilience.

The latest research from Public First, which we commissioned alongside Aviva and Flood Re, speaks directly to that agenda. The Environment Agency’s national assessment found that around 4.6 million properties in England are in areas at risk of surface water flooding, a 43% increase on its previous study. In new developments, heavier rainfall, the current approach of site-based measures are not always enough, and more property-level resilience measures are needed. Without this, it can affect homes, construction sites, sales activity, insurer and lending confidence and the viability of future development.

Much of the debate on flooding has rightly focused on households and public services. But Public First’s analysis highlights another important part of the picture: the commercial exposure developers face when flooding happens during construction and active sales periods. A flood event before a site is fully built out can create remediation costs, delays, financing pressures, disruption to buyer confidence and potential reductions in the value of unsold homes.

Property flood resilience measures can be integrated at dwelling level to help resist flooding and reduce its impact where water does enter homes or affects a development during construction. Examples can include raised electrics, additional waterproof membranes, resilient materials, self-closing air-bricks and non-return valves designed to reduce damage and speed up recovery. These measures eliminate water ingress points into a home, using resilience materials that both resist water and recover from contact with water, and do not need to be replaced. Importantly, they are also generally low-cost when incorporated during construction, with evidence suggesting a reasonable package costs around £1,000 per dwelling. ¹

The new modelling, summarised here by Public First suggests that relatively modest property-level flood resilience measures, installed during construction, can help reduce these risks. Across the scenarios tested, for every £1 spent on these resilience measures, developers could save around £2.27 by avoiding delays due to flooding during construction and completions, remediation works, disruption to active sales periods and impacts on pricing assumptions for unsold homes.

The strongest relative return was found in the London scenario, where a smaller, dense urban development in Lewisham produced a benefit-cost ratio of 2.57. That finding is especially relevant during London Climate Action Week because it shows that adaptation is not only a public policy issue; it is also a commercial and investment issue.

London Climate Action Week brings together policymakers, businesses, investors, civil society and communities to accelerate practical climate action. Flood resilience should be part of that conversation because it sits at the intersection of housing, infrastructure, insurance, finance and public confidence. If we are to keep building the homes we need, resilience must be designed in from the start, and this research demonstrates the economic benefits of doing so.

The message from this research is straightforward: better flood resilience can support more reliable housing delivery, protect households, reduce disruption and strengthen confidence in new development. During London Climate Action Week, that is exactly the kind of practical, evidence-led climate action that deserves attention.