## 4 Discussion  
Several factors should be considered when interpreting the quantitative results. One of them is that there is uncertainty in the scenarios for climate change, and only one of the available alternative RCP greenhouse gas emission scenarios is used in this study. However, the impact of the choice of RCP4.5 on the results is relatively small. Moreover, there are other sources of uncertainty in TRY2050, arising from internal climate variability and climate modeling. In our study, the climate change scenarios for the future are derived from a large sample of climate models [35] which increases confidence in the scenarios in comparison to using just a single model. Furthermore, technical development, improvements in building practices, and socio-economic changes are hard to be considered for the future. Another factor in the building simulation model is occupancy profiles which affect the accuracy of the results. In this study, the presence of occupants has been assumed in a way that is as close as possible to the modern lifestyle of families. Using the fixed and continuous heat gains may cause different results. Regarding the overheating risk, Finnish regulations for the temperature limits are used in this paper, and in other Nordic countries, the temperature limits may differ. For example, in Denmark, the degree hours above 26 \({}^{\circ}\)C are recommended to be less than 100 Kh [48]. These limitations must be taken into account when the results are interpreted internationally. Despite these limitations, the severity of the effects of climate change on the health and thermal comfort of residential buildings occupants are not questionable, especially in the Nordic countries where most of the residential buildings are not typically equipped with mechanical cooling systems. According to the present simulations, the degree hours above 27 \({}^{\circ}\)C will increase in the future climate by more than 50% in both the old and new buildings. During the current and future heatwaves, the degree hours above 27 \({}^{\circ}\)C increase up to 10,000 Kh and 14,000 Kh, respectively, in both old and new buildings. In almost all the cases without mechanical cooling in the new building under the current and future climate, the degree hours above 27 \({}^{\circ}\)C are significantly higher than the required number of 150 Kh in the Finnish building code [27]. This shows that except for the openable windows, other building measures are not able to guarantee to fulfill the building code requirement, and only with the usage of the split cooling unit, the new building may fulfill the 150 Kh requirement. Although the national requirements do not apply to existing buildings, exemplified here by the old building, results for it are worth to be considered. The degree hours above 27 \({}^{\circ}\)C in the cases without mechanical cooling in the old building are significantly higher than 150 Kh in the current and future climate. Moreover, none of the building measures introduced a guarantee that the old building can fulfill the requirements. Thus, this indicates a high risk of overheating in the old building. In the future climate and during extreme weather conditions, the situation will be even worse in both old and new buildings. Thus, it seems to be important to revise the regulations of building stock renovation and design practice considering climate change and its effects on the health and comfort of occupants. Moreover, providing common requirements for residential buildings in Nordic countries or the whole of Europe would be worth considering while there are globally common standards and design practices for commercial buildings [49; 50]. In most cases, the maximum indoor temperatures exceed 32 \({}^{\circ}\)C without mechanical cooling. The threshold value of 32 \({}^{\circ}\)C is the upper limit for the health of occupants in all the living spaces for both existing and new buildings in Finland [28].