<p>Housing retrofits constitute an important pathway for reducing residential energy consumption and advancing decarbonization in rural China. However, uptake remains limited due to information asymmetry, technical uncertainty, and relatively weak formal institutional support. Drawing on micro-survey data from 855 rural households in Hainan Province, this study examines how social capital and low-carbon cognition are associated with residents’ willingness to undertake decarbonization-oriented housing improvements. Logit, mediation, and heterogeneity analyses yield three main findings. First, social capital—operationalized through social trust, social norms, and social networks—is positively associated with retrofit willingness and can be understood as an informal social resource in rural contexts. Second, low-carbon cognition is also positively associated with retrofit intention and is related to the relationship between social capital and willingness through an indirect pathway. Third, these relationships vary across household characteristics. This study contributes to the housing retrofit literature by highlighting that retrofit decisions in rural China are closely linked to socially embedded processes and cognitive factors shaped by community interactions, complementing explanations based on formal institutional arrangements.</p>