ZEMCH 2015 - International Conference Proceedings | Page 733

Figure 14: Cross ventilation within 2 openings (Wood and Salib 2012)
Allard describes in his book (2002) the effect of the roof shape and how much it could effect on the
ventilation and the wind speed and direction. And this supports the idea of designing inclined
roofs which are directed according to the wind flow. The efficient case is inspired by the aerodynamics of the cars, and for that, roofs were inclined to decrease the amount of incident south solar
radiation, simultaneously, it facilitates the strategy for ventilation. When the wind is coming from
the North West pass smoothly, it makes a cross ventilation through windows and passes parallel
to the roof surface cooling down the temperatures outside, and refreshing the air inside.

Figure 15: Roof types and the characteristics of the building envelope that effect on the wind performance (Allard 2002)
Figures 15 illustrate the relation between the wind and the impact of the building roof shape on
the wind characteristics. When the building is elevated – and the roof is sloped towards the wind
side- it facilitates an easy movement of the wind, and enhances wind speed that cross over the
roof; as it will move from the positive pressure to the suction zone, and after that create a vortices behind the building; to cool it down. This is matching the idea applied on the efficient case
where the building platform was elevated, and the roof was designed with an inclination on the
windward. These factors as an overall help the building work as Allard (2002) mentioned in his
predictions methods related to the natural ventilation perf