To what extent can outdoor heat adaptation measures in urban districts help to reduce high indoor temperatures in buildings and thus enhance indoor thermal conditions? To answer this question microscale meteorological simulation (MMS) and building performance simulation (BPS) are combined in a model chain approach. Two existing residential German districts with different urban designs are modelled in the MMS tool ENVI-met. For both districts, a representative residential building (one from the Wilhelminian period and one large panel construction type) is modelled using the BPS tool IDA-ICE. Different scenarios of heat adaptation measures are applied to analyse how changes in urban and building design (e.g. white (cool) roofs (high albedo), white traffic areas (high albedo), intensive green roofs, urban trees, facade insulation or facade greening) affect outdoor and indoor temperatures. The MMS results highlight that the district from the Wilhelminian period is less heat resilient and that the efficacy of heat adaptation measures on heat reduction in open space depends on the urban design and the daytime. Regarding the efficacy of heat adaptation measures on indoor thermal conditions, our findings indicate that the larger share of the indoor cooling effect is not caused by the outdoor air temperature reduction by the outdoor heat adaptation measures but by the change of the building physics in the BPS model (e.g. changing the surface reflectance of the white roofs). White roofs and intensive green roofs show the largest cooling effect by reducing the operative room temperature by more than 1 Kelvin. Our findings also demonstrate that facade insulation can act as both, climate adaptation and mitigation measures.