Abstract: Energy consumption has become a major concern of global discussions among engineers, architects, scientists and planners. There are many ways to tackle this issue by saving energy in many sectors. Lighting is one way used to saving energy as it is used in many applications and it is one of the areas to be addressed for improving the energy efficiency in order to reducing the energy consumption. Natural daylight inside space considered one of the most important affairs because of its importance in caving energy consumption and its ability to provide a comfort environment inside space for occupants. Daylight in the residential building is a Major shareholder to save the energy consumption because it is the most significant natural resources available to engineers and architects to improve the visual comfort quality of interior spaces. A considerable reduction in artificial lighting and energy consumption can be achieved by maximize the use of natural day lighting. So, strategies are needed for more daylight optimization in the residential building spaces where electricity demand is very high. There are some design factors which architects should consider, namely: fenestration, climate conditions, orientations, and shading devices. As it is known that windows are the greatest resource to allow daylight into buildings, and proper window design also improves the thermal comfort and produces a significant energy savings in electric lighting. This paper aims to study the effect of Window-Wall Ratio (WWR) in Multi-Story Residential Building as one of the passive design strategies to optimize daylighting in residential buildings in Mansoura City, according to the framework of the Egyptian construction law which puts a lot of parameters which effect the daylighting of buildings, including buildings height and its relationship to the street width in addition to linking windows area of the residential spaces with the residential spaces area , thus to find a relationship between the percentage of housing openings and the elevation angle of the opposite buildings depending on the requirements of the global natural lighting and compare that Egyptian law. Rhino as a recommendation for building designers to use it at the early stages of design. This study was carried out by simulations on rhino software by using diva plugin in rhino program for calculation of daylighting during living hours. An investigation on the optimum amount of window size has been done by studying a living room model with 5.4m 3.6 m 2.7 m dimension expanding in vertical and horizontal level.

Keywords: Daylight, Window Wall Ratio (WWR), Residential Building, Diva for rhino simulation software, Daylight Autonomy.