The microclimate plays a crucial role in the conservation of historical cult buildings and their artifacts for future generations. In order to conserve these buildings and their artifacts, it is imperative to ensure that the microclimate is conserved. The norms and standards existing so far in Latvia do not stipulate thresholds for air parameters that would ensure a conserving microclimate for historical cult buildings. In order to identify these thresholds, the air parameters were measured simultaneously at nine measuring points within the Krimulda Church (LV) of the 13th century. The temperatures of the surfaces of the building envelope and potential condensation were calculated using the actual data of indoor and outside air. The indoor and outdoor air humidity ratio was calculated for each measurement. The conservation threshold of indoor microclimate parameters was determined by using intermittent heating on the basis of the air parameter fluctuations and calculations. The moisture vapours from the building structures were quantified in this research. The indoor humidity ratio during the warm season and the upper threshold during the heating season were determined.