From Vernacular Environmental Functions to Climate-Ready Circular Rehabilitation: An Integrative Evidence Synthesis with a Spanish Climate-Zone Application

Vernacular architecture is widely invoked as a source of low-carbon and climate-responsive design knowledge, yet the climatic regimes, occupancy practices and maintenance systems that generated this knowledge are becoming non-stationary. This study develops a structured integrative evidence synthesis for the climate-ready circular rehabilitation of vernacular buildings and applies the resulting framework to a previously published municipal climate-zone dataset for Spain. The review is organised around four research questions addressing passive environmental functions, material and assembly compatibility, maladaptation pathways and future-climate decision priorities. Evidence is coded through a causal chain linking climatic exposure, physical mechanism, performance variable, boundary condition, failure mode and monitoring indicator, and is appraised at claim level according to methodological strength, climatic relevance, mechanism clarity, observation scale and reporting of adverse effects. The synthesis demonstrates that transferability depends less on reproducing vernacular forms than on preserving the environmental source, heat or moisture sink, and operating window that make a strategy effective. Retention and repair provide the highest circular value, whereas earth-, lime-, timber-, cork-, plant-fibre- and reclaimed-mineral systems deliver robust benefits only when moisture transport, junctions, fire, biological durability, workmanship, service life and end-of-life are evaluated at assembly scale. The Spanish application reuses 7966 municipal classifications for present conditions and Representative Concentration Pathway (RCP) 4.5 and RCP 8.5 horizons in 2055 and 2085. Complete climate-zone labels change in 84.2–85.0% of municipalities under RCP 4.5 and in 93.2% under RCP 8.5; by 2085 under RCP 8.5, 88.9% move toward lower winter severity, 66.1% toward higher summer severity and 85.4% are assigned to summer class 4. These data are not claimed as a new climate dataset; they are used to test the decision implications of climate non-stationarity for vernacular rehabilitation. The principal contribution is the Function–Compatibility–Adaptability framework, which converts heterogeneous evidence into sequential and falsifiable decision gates: recover passive function, verify coupled compatibility, minimise irreversible material addition and define monitoring triggers before intervention. The framework is further operationalised through a practical decision workflow to support climate-ready rehabilitation of vernacular buildings. The framework provides a scientifically explicit bridge between vernacular knowledge, conservation science, building physics, circular construction and future-climate adaptation.