a meditation on the boundary as an active zone, through an investigation of the vernacular architectural element ‘Mashrabiya’
“For physicists… the boundary is not a thing, but an action. Environments are understood as energy fields, and the boundary operates as a transitional zone between different states of an energy field. As such it is a place of change as an environment’s energy field transitions from a high-energy to low energy state or form one form of energy to another. Boundaries are therefore, by definition, active zones of mediation rather than of delineation.”(1)
Historical and Cultural significance of the Mashrabiya
The Mashrabiya can simply be understood as a two dimensional perforated screen. Mostly found in urban setting the mashrabiya appears across the Islamic world, holding cultural and spiritual significance. It is a sign of wealth and prosperity, due to its intense intricate craftsmanship. The patterning has both social and environmental functions; it prevents an occupant from being seen from the street level and it allows air to circulate. Take a virtual tour of Bayt Al-Suhaymi to see the beautiful effect of the mashrabiya.
Desert climate and why shading is important
Why does the desert experience extreem diurnal temperature variations?
High desert areas typically have the greatest diurnal temperature variations. Low lying, humid areas typically have the least. Biomes that are protected by their humidity (water vapour in the air) retain heat and energy that is experienced during daylight hours. At night the water re-radiates the heat absorbed back into the atmosphere. The more energy that is required to change the temperature of a highly dense material is said to have a high thermal mass.
To achieve thermal comfort in hot arid climates a combination of elements should be used. During the evening the effects of thermal mass should be present and during the day cooling should be introduced. A three tier design approach is a sustainable way in which spaces may be designed. The first tier consists of heat avoidance, by minimising heat gain through appropriate use of shading and orientation. The second tier response is to passively cool via a form of ventilation. When working with openings and perforated surfaces light and ventilation should be considered simultaneously.
The mashrabiya is a popular wind-catching feature in the Arabic Middle Eastern architecture which responds to the first 2 methods of cooling. First seen in the west districts of Saudi Arabia and afterwards in many regions with hot-arid and hot-humid climate; They were placed at the finish- ing of an opening, sometimes smaller (row- shans) and other times bigger, even at the finish- ing of a whole façade (mashrabiyas). It is a multifunctional element which, controls daylight, air flow, reduces temperature of air current, increases (indirectly) humidity of air current and ensures privacy. Indirect evaporative cooling cools the incoming air of the building without raising the indoor humidity as opposed to direct evaporative cooling where water is sprayed into the air entering a building, lowering the air temperature but raising its humidity.
Intelligent and Adaptive Façade System: The Impact of Intelligent and Adaptive Façade on The Performance and Energy Efficiency of Buildings
“Wind passing through the interstices of the porous- wooden mashrabiya will give up some of its humidity to the wooden balusters if they are cool at night. When the mashrabiya is directly heated by sunlight, this humidity is released into the air that may be flowing through the interstices…The balusters and interstices of the mashrabiya have optimal absolute and relative sizes that are based on the area of the surfaces exposed to the air and the rate at which the air passes through. Thus if the surface area is increased by increasing baluster size, the cooling and humidification are increased. Furthermore a larger baluster has not only more surface area to absorb water vapour and the serve as a surface for evaporation but also more volume, which means that is has more capacity and will therefore release the water for evaporation over a longer period of time.”(3)
varying thickness of the surface and diameter of inlet and outlet. The shape, a circle, has been arbitrarily chosen.
a) varying diameter of opening changes the velocity at which wind enters the spaceb) increasing thickness of screen will decrease amount of direct daylight and as an extension, heat
c) If inlets and outlets vary, the inlet should be smaller to maximise velocity
d) tapering surface provides advantageous self shading properties over inlets
Their sizes also depend on the size of the opening, which is mainly influenced by the type of climate. By modulating the size, thickness, density and overall organization of the pattern, different environmental effects can be achieved such as controlling the orientation of light or the movement of air.
“The volume of the balusters and the sizes of interstices directly affect the temperature as well as the level of humidity and glare within the room”
Interstices were required to be smaller at seating and standing height to reduce glare and retain privacy, the resulting reduction in airflow would be compensated for by larger interstices higher up in the latticework. Therefore interstices are directly proportional to airflow and amount of luminance. The effect is similar to Western clerestory windows employed in Western Architecture.
The characteristic shape of the lattice with its lines interrupted by the protruding sections of the balusters produces a silhouette which carries the eye from one baluster to the next across the interstices, vertically and horizontally. This design corrects the slashing effect caused by the flat slats of the brise- soleil, first introduced by Le Corbusier. The horizontal form of the brise-soleil results in a binary definition between light and dark, where as the intricate patterns created in the mashrabiya provide ample surface for light diffuse.
(1) M Addington and D Schodek, Smart Materials and Technologies for the Architecture and Design Professions, Architectural Press/Elsevier (Oxford), 2005, p 7.
(2) Lechner, Norbert. Heating, Cooling, Lighting: Sustainable Design Methods for Architects. Hoboken, NJ: John Wiley & Sons, 2009. Print.
(3) H Fathy, Natural Energy and Vernacular Architecture: Principles and Examples with Reference to Hot Arid Climates, University of Chicago Press 1986 pp48-49
Thomas Schielke. “Light Matters: Learning From Vernacular Windows” 09 Apr 2015. ArchDaily. Accessed 24 Feb 2016. <http://www.archdaily.com/617266/light-matters-learning-from-vernacular-windows/>