Traditional cost-benefit analyses (CBAs) of flood risk reduction measures usually ignore distributions of damages over populations, which disadvantages the poor. Instead, a CBA based on social welfare includes individual social vulnerability through relative impacts on consumption. If vulnerabilities are high, floods are catastrophic and cause poverty, migration or indirect deaths, and risk reductions have high social welfare values. For non-catastrophic risks, social welfare values of risks are relatively higher for vulnerable low-income households. We present a framework to integrate social vulnerability into CBAs, and show how financial protection reduces social flood vulnerability and provides welfare benefits. A case study illustrates that traditional CBAs underestimate the social welfare value of flood risk reduction measures, up to a factor of 30. Data on financial protection is however scarce, which hampers estimation of the social welfare value in practice. A solution is to increase financial protection of individuals, in addition to offering physical flood protection.