Climate change with more frequent and longer heat waves in the future will be a challenge for the cities in Sweden. With more frequent heat waves the demand for mechanical cooling will increase. This will lead to higher energy consumption with the consequence that the emissions of greenhouse gases increase and affect climate change even further. To avoid thermal discomfort during the summers the design and constructions in the building have central roles. Sun protecting measures like awnings and shadings as well as window airing can have a large impact on the indoor temperature. This study investigates how different climates affect the indoor temperature in buildings and the results illustrate the problems with thermal comfort that can arise. Additionally, long lasting technical solutions to mitigate high indoor temperatures during heat waves were evaluated. The results show how different prerequisites, as well as common solutions, for buildings affect the thermal comfort. They also identify the importance of a holistic system view of the building during the design so that the thermal comfort aspects are considered together with energy improvement measures.