Climate change is projected to intensify indoor humidity, dampness, and mould growth, but its impacts on indoor environments are not sufficiently addressed. This study investigates how future climate scenarios will influence indoor relative humidity and mould risk in a timber-framed building case study, where moisture sensitivity is high. A representative community office building in Auckland was modelled using EnergyPlus to simulate current and future (2050 and 2070) indoor hygrothermal conditions. Hygrothermal risk indicators, including relative humidity and temperature factors, were assessed against recommended thresholds to identify conditions conducive to mould growth. Thresholds followed conservative guidance for mould prevention, focusing on hours above critical relative humidity (RH) bands and air temperature in occupied spaces. Results show a significant rise in indoor humidity and the total hours exceeding low risk thresholds, particularly in July, the coldest and most moisture-prone month of the year in Auckland. The increase is most pronounced under 2050 and 2070, indicating a shift from intermittent to more persistent high RH and temperature exposure during winter. This work provides evidence-based guidance informed by robust datasets and reproducible analyses for updating building codes and designing climate-resilient, healthy indoor environments across New Zealand.