This article analyzes the indoor climate that creates risk of damages in naturally ventilated churches in the cold climate of Estonia. Indoor temperature and humidity were measured over a one-year period and the results were analyzed on the basis of damage functions: mold growth, risk of cracking and fracturing of wooden objects, and delamination of the gesso layer of panel paintings. In unheated churches, one of the most dominant problems was very high relative humidity throughout the year, creating a high risk for mold and algae growth. Churches may need background heating to avoid freezing during a long cold winter that causes low surface temperatures of massive walls during the spring–summer period. It was found that mold risk was significantly lower in heated churches than in unheated or intermittently heated churches. The risk of mold growth was not decreased by the use of intermittent heating. In heated churches, overheating (room temperature >+10ºC) causes a RH below 50% during cold periods, and the favorable period for irreversible response of panel paintings was significantly longer, so there is a higher risk that the gesso may crack or delaminate. From the point of view of the cracking and fracturing of wood, indoor climate conditions are in the safe range for most of the year.

Estonian cost optimal and nearly zero energy building (nZEB) energy performance levels were determined for the reference detached house, apartment and office building. Cost optimal energy performance levels, i.e. the energy performance leading to the lowest life cycle cost according to defined methodology, are implemented into new Estonian energy performance regulation as minimum requirements for new buildings. The regulation that came into force since 9 January 2013 includes requirements for nZEB buildings, but they are not mandatory. Compared to previous requirements, cost optimal requirements improve energy performance by 20%–40% depending on the building type and energy sources used. The results of the reference office and apartment building are reported. The results of the reference detached house, being previously reported, have been recalculated with new energy carrier factor for electricity, which was one major change in the regulation in addition to new requirements. When the detached house showed global cost curves with well-established cost optimal points, global cost curves were much more flat for the apartment and office building. This indicates that the results are sensitive to input data and relatively small changes in input data can significantly shift the cost optimal points. As uncertainties related to nZEB performance level and cost calculation are generally much higher due to high performance technical solutions not commonly used and costs not well established, it is recommended to repeat nZEB calculations with possibly refined input data before setting mandatory nZEB requirements.

Full-scale laboratory measurements were taken and 2D simulations were performed to determine the moisture convection performance of the joint of an external wall and an attic floor. Both the measured and simulated results showed that the building fabric is locally sensitive to exfiltration airflow as moisture convection could cause a remarkable increase in the moisture accumulation rate on the inner surface of the sheathing. The results prove that in modern houses with balanced ventilation, where the positive pressure caused by the stack effect cannot be easily controlled, it is essential to control moisture convection by good airtightness and the use of assembly solutions with improved hygrothermal performance, such as the case with mineral wool sheathing that was tested. The simulated results showed that the use of a constant moisture excess value instead of the profile did not cause any inaccuracy in the moisture content. At the same time, the use of the constant outdoor temperature over a long time period did change the hygrothermal performance, which became significantly more critical when simulated with variable outdoor temperatures. The laboratory measurement and simulation results show that in a cold climate, for the assemblies being studied with mineral wool sheathing, leakage rates of 0.1—0.2 L/(s·m) at a 10 Pa pressure difference may be used as performance criteria for moisture convection in a two-storey house with dimensioning moisture excess 4 g/m ³ and a cold outdoor climate. Previous studies on the leakage characteristics show that these leakage rates are easily achievable in practice with careful workmanship.