The history of Mashrabiya is an important fact, but it cannot alone explain why the Mashrabiya became so widespread. Therefore it is necessary to know and study the role and functions of Mashrabiya within buildings. 

Fathy asserted (in 1986) that Mashrabiya has, in general, five functions, and many models of these have been developed to describe ways of coping with the different conditions affecting one or more of these functions. The main functions are :

Fathy accepted wooden lattice as Mashrabiya, if it was able to provide some or all of these functions. He also suggested that to achieve any function, there are terms of design concerning the choice of the distances between adjacent balusters and the radius of each of them. According to the different designs, there are many models of Mashrabiya that are known by different names.

Natural light is one of the  most important matters in architecture, as Louis Kahn described a room is not a room without natural light. But it is not only advantageous; there are three issues that need to be controlled:

• The heating caused by direct solar gain.

• The internal daylighting requirements.

• The visual qualities of light, such as glare.

There are three types of daylight:

1. - Direct light

2. - Diffuse skylight

3. - Reflected glare

Mashrabiya can effectively deal with these three kinds and solve the problems by changing the light from something harsh and undesirable to a highly favorable and lovely feature of internal space. And it should be mentioned that the effect of internal daylight varies depending on the direction, for example it is preferable to block direct light entering from the southern openings, because it causes the surfaces to heat up inside the room, even though the glare from this direction does not cause any heat, it can cause an optical inconvenience (Figure 3.2). 

Openings from the north do not cause any problems. Accordingly, the design of Mashrabiya with a south façade differs noticeably from the design in a northerly one. A Mashrabiya with a carefully calculated design is able to adjust exactly to what type of light should enter the building (Figure 3.3).

Direct light is intensified light, which has an acute angle falling on the surface of the aperture level (Fathy, 1986). Mashrabiya is able to control when and how much direct daylight could enter the building during summer or winter according to the parameters of Mashrabiya design which the architect determines. It blocks the troublesome sun, decreases internal heat gain during summer and allows for a small amount of light to enter during winter (Figure 3.4).

According to Fathy’s principles (1986), this requires a lattice with small interval distances between the balusters at eye level, in order to prevent direct light in summer. While in winter it works in the opposite way, when the sun’s angle is lower in the sky and can pass through the interstices of the same Mashrabiya, and provide some warmth to the room . To compensate for the decrease in the amount of lighting in this design, it is preferable that the spaces between the balusters are made much wider in the upper parts of the façade, as shown in the example which is taken from Jamal al-Din alZahabi’s house in Cairo, Egypt Figure (3.5).

It is possible to install a small sunshade above the aperture to prevent direct sunlight from entering (Figure 3.6)

In north interfaces, where direct sunlight does not cause any problems, Fathy always preferred to make the separation distances between balusters wider, to provide adequate light for rooms.

It is the required adequate daylighting which the internal spaces need to allow for regular activities, and it is essential in hot climates to create good internal situations without being bothered by excessive heat gain.

Even if we need to block direct sunlight in the troublesome times, we still need enough natural internal light for regular, daily activities. Mashrabiya is an important element that allows ambient light to pass into spaces without letting in direct sunlight. The quantity of diffuse skylight that goes into a room relies primarily on the important parameters that control how much ambient light can enter the building. These parameters, according to Samuels (2011) are: the size and porosity of the Mashrabiya, along with the reflectivity and materiality of the balusters.

It is less intense light and enters almost perpendicularly on the surface of aperture level (Fathy, 1986). Glare doesn’t raise the temperature of the room, but it causes an optical inconvenience. To solve this problem Mashrabiya is one of the best effective choices. In this case the architect have to choose a Mashrabiya with a circular section for the balusters as a main condition. 

That means the gradual shadow which is created by rounded blusters, reduces any contrast, unlike the square sectional balusters, or any other similar shading devices. This is a common mistake, which is repeated in some modern projects which use the Mashrabiya without taking into account this important condition, especially when using steel material in the construction of Mashrabiya (Figure 3.7).

Figure 3.8 shows the impact of Mashrabiya if there is a bright light, and how it produces a shaded image which moves the eye between the rods through spacing, horizontally and vertically, thereby invalidating the slashing effect which is caused by the flat slats used in brise-soleil Figure (3.9). Fathy (1986) also saw that Mashrabiya excelled in other types of window by working on matching the external views harmoniously through the full aperture, above the decorative pattern to the Mashrabiya, so Mashrabiya becomes like a piece of dark glass which is woven by ‘threads’ (Figure 3.10). In this way the view beyond is exposed, while maintaining privacy without any of the heat gain problems previously discussed.

Evaporation is one of the most important techniques used to cool buildings in hot climates, and to make this process continuous and effective, the airflow needs to be strong enough to carry the released water vapor away, and thus provide heat transfer.

On this point it is important that buildings in harsh climates have a steady and uninterrupted internal airflow, so it is necessary to fully understand the effect of the design and the size of Mashrabiya. Further points concerning ventilation; Mashrabiya is used to ensure air circulation inside the building, air is pulled into the room through the small interstices of the Mashrabiya in the lower part and hot air is ejected out through the large interstices of the upper part. This technique not only enhances the air circulation but also speeds it into other indoor rooms.

When the temperature of the air diminishes, its size decreases, per contra the weight and density of it increase. The output rise in the air pressure drives the air to blow into the internal spaces through the small interstices. As the air temperature increases, the size of air increases also, while its weight and density decrease, therefore low pressure makes the air move upwards and out of through the large interstices in the upper part of the Mashrabiya. It is worth mentioning that the rounded surfaces of the latticework of Mashrabiya provide a smooth airflow. For the winter and in cold climates, the Mashrabiya can be prepared with glass shutters and solid wood (Lane, 1977). 

To get more airflow, different pressures may be created between the inside and outside of the building, by openings on opposite walls of the room. The size of these openings and the porosity of the Mashrabiyas which enclose them are the decisive factors in the flow rate between the two. If the interstices constitute 80% of the total Mashrabiya area (Porosity Factor [PF or φ] = 0.8) then the airflow through the opening will be at 80% of what it would have been with no Mashrabiya in place (Gandemer and Alain, 1981).

A Mashrabiya with large interstices provides adequate airflow, when considerations relating to the light require narrow interstices and thus impedes sufficient air flow, in this case the architect can use the large open interstices pattern of Mashrabiya in the upper part, near the overhang, or increase the size of Mashrabiya, even to the point of covering the entire elevation of the room (Figure 3.11).

Sometimes the Mashrabiya was used by Fathy in interior design, between rooms, to supply the ventilation from more than one side of the building.

The air which passes through the wooden Mashrabiya, loses some of its humidity by the absorption property of the wooden balusters; if they are cold, as usual at night, and when the Mashrabiya is heated by direct sunlight, this humidity is absorbed by the air which flows through the porous wooden Mashrabiya (Figure 3.12). This technique is efficient in making dry air more moist in the heat of the day, humidifying and cooling it at a time when most needed.

With regard to the foregoing, it should shed light on the importance of the wood chosen for the construction of Mashrabiya, and take into account that new alternative materials should have properties which are more or less similar to wood, in relation to absorption and evaporation matters. 

For additional cooling by evaporation, the water jar can be used, placed behind the lattice of Mashrabiya, where the air flow gets cooled due to the evaporation of water from the jars, this process is known as evaporative cooling (Briggs, 1974) (Figure 3.13).

There are many recognized ways to adjust the temperature of buildings, like using walls with large sections and a high thermal inertia, shading the interiors, designing small apertures, and a smart combination of architectural elements that work together to reduce heat gains and create a perfect internal environment (Dayyoub, 2001). 

We are all aware that direct sunlight is the reason for high temperatures, and the Mashrabiya limits the solar gain by shading the inner spaces during the hot summer months, but is able to supply some heat in the cooler months of the year, by allowing direct daylight to enter the building during winter. The cooling and heating processes rely on specific features of the lattice in terms of its sizing and porosity; a more porous lattice will allow for more direct light in the cold days but also raise the airflow through the space, and change the capacity of the evaporative cooling systems.

So it is important to fully understand each function separately, to determine the effects each have on the others, and how all of them work together to create comfortable thermal and visual conditions for internal spaces.

As mentioned in chapter two, the widespread popularity of Mashrabiya in Islamic countries could be attributed to the visual privacy factor. Mashrabiya provides privacy for occupants from the outside, while allowing them, at the same time, to look out through the lattice. If the Mashrabiya is overlooking the street the distances between the balusters are preferably small at eye level, except for the upper part above eye level.

Figures 3.14 and 3.15 show an excellent example of how Mashrabiya can provide a view to the outside without losing the privacy factor which gives the resident a feeling of reassurance, as Fathy (1986) showed by focusing on the lattice, the Mashrabiya seems like a lighted wall, conversely, with the focus beyond the lattice, the external view is fully obvious, and only slightly obscured. 

This is an important feature of the Mashrabiya, but it is no longer possible when glazed windows are used, as they block the connection between internal spaces and outdoors.

The different patterns of Mashrabiya imbued life and vibrancy to the façades of traditional buildings which were previously extremely bare and gave a solid and harsh impression due to the heavy walls (Figure 3.16).

The more complicated and detailed the Mashrabiya is, the more expensive it is; that is why it became highly desirable as a symbol of wealth. In this way the decorative features of the Mashrabiya became something of a social statement. Additionally, it should not be ignored that the Mashrabiya is an important expression of Eastern identity.

The traditional Mashrabiya provides an important property of being directional or maintaining a configuration, conformation, contour, form, shape and any spatial attributes (especially as defined by outline) to create a space which can be used for many functions as mentioned before, like a seat for the ladies to overlook outside , or to put a jar of water to get cool.