## 4 Discussion
For elderly people who are cared for in the residential living spaces, this maximum value is reduced to 30 \({}^{\circ}\)C [28]. The new building has the lowest degree hours above 32 \({}^{\circ}\)C with 1 Kh in the current climate and 39 Kh in the future climate. These degree hours will reach more than 1000 Kh in both building types during heatwave summers of 2018 and 2050. This overheating may cause serious health problems for the occupants. A study in Finland showed that the heatwaves in recent decades have caused about 200 to 400 excess deaths in Finland [6]. Thus, Solar protection windows, openable windows, split cooling units, and ventilation cooling and ventilation boost can effectively reduce the degree hours above 32 \({}^{\circ}\)C in both buildingtypes in the current and future climate. Hence, to avoid the health risks of overheating, the building stock needs to change in design and renovation phases to cope with the future extreme and average climate conditions. Orientation, blinds, and site shadings are not significantly effective on overheating risk and energy demand. Other passive strategies like solar protection windows improve indoor temperature conditions but cannot alone fulfill the temperature requirements. Openable windows are the most effective studied passive strategy in the new building, being able to reduce the degree hours above 27 \({}^{\circ}\)C to the acceptable range in the current and future climate. However, they are not effective enough for the fulfillment of the temperature requirements in the old buildings. It is also important to note that based on the regulations, openable windows are not allowed to be used for the fulfillment of indoor temperature requirements in the design phase of new buildings [29]. Although opening the windows can bring fresh air inside and reduce the overheating risk, it should be considered that by opening the window, indoor air quality and indoor acoustic conditions will be affected by the outdoor conditions. Moreover, there are security issues with opening the windows. Overall, building measures may improve the indoor temperature conditions under changing climate but they seem not to be sufficiently effective. The maximum indoor air temperatures are significantly higher during the heat-wave summer of 2018 than during the average present and future climates (TRY2020 and TRY2050). The increase in the indoor air temperature is even a more serious issue in the heatwave summer of 2050. The results show the high risk of overheating in the residential buildings in the current and future climate of Finland. To decrease the indoor temperature during the heatwaves, mechanical cooling systems should be implemented. Based on our simulations, the space cooling electricity consumption increased during the heatwave summer 2018 in a way that it was higher than the amount in the current and future average climate in both building types, and in the heatwave summer of 2050, the increase would be even higher. Mechanical cooling systems, like split cooling units or cooling of ventilation supply air, are required to reduce the indoor air temperature effectively in the future climate. According to the present results, the energy consumption of split cooling units is below 3 kWh/m\({}^{2}\) in the current climate and will reach 4 kWh/m\({}^{2}\) in future climate. Typically, in Finland, the cost of a split unit is about 2000 euro for the equipment and installation. However, this cost level is reasonable for reaching the indoor temperature target values. Since the benefits of acceptable indoor temperature on the well-being and comfort of the occupants are not questionable. Moreover, the energy needed for cooling can be partly provided by free cooling from outdoor air or ground-coupled systems. However, the efficiency loss of these free sources due to the high outdoor air temperature during the heatwaves should be considered.