roof window

EN 16798-7:2017 considers that windows on roofs that have a pitch below 60° are not included on the windward side whatever their orientation. It means that roof windows are accounted for, but only on the leeward side when using the existing standard for calculation of air flows, EN 16798-7.

Therefore, in the specific case of a room only equipped with roof windows (e.g. an attic) and aeraulically independent from the rest of the building, whatever the orientation of the roof windows, only the simplified “singlesided” calculation method of EN 16798-7:2017 is applicable.

The effects of roof window on ventilation flow rates and reduction of cooling loads in densely populated areas were investigated by using building simulations. In May of the intermediate season, when utilizing roof window, the cumulative number of air exchanges increased by 9 % to 12 % compared to that when the windows at side walls remained open only during the daytime. When the building coverage ratio increased from 0 % to 20 %, the cumulative number of air exchanges decreased and the cumulative cooling loads increased.