Solar Insolation Requirement the Reason for Overheating in Nearly Zero Energy Apartment Buildings

Estonian Governmental Regulation „Minimum Requirements for energy performance“ that regulates the construction of Nearly Zero Energy Buildings (nZEB) states that the requirement for summertime indoor temperature is regarded as complied with if, during the period from 1 June to 31 August, the indoor temperature does not exceed the limit temperature (the cooling setting) of 27°C by more than 150 degree hours (°Ch) in residential buildings. At the same time Estonian standard “Daylight in dwellings and Office“ states that all the new apartments have to have at least three hour lasting constant direct solar access from 22.April until 22.August including June 22 nd. The requirement means that it is challenging to design balconies to block the direct solar access during the warmest period of the year. As a consequence overheating problems in new apartment buildings exists. This paper gives recommendation how to modify the solar insolation requirements for apartment buildings in a way that there will still be solar exposure in the apartments but without overheating the rooms.