Figure 17: roof form

climate as they can be used for sleeping at night in summer as well as for daytime activities in winter. The material of the roof should be massive; a reinforced cement concrete (RCC) slab is preferred to asbestos cement (AC) sheet roof. External insulation in the form of mud phuska with inverted earthen pots is also suitable. A false ceiling in rooms having exposed roofs can help in reducing the discomfort level. Sodha et al. have reported that the provision of roof insulation yields greater lifecycle savings compared to walls in this climate. Evaporative cooling of the roof surface and night-time radiative cooling can also be employed. In case the former is used, it is better to use a roof having high thermal transmittance (a high U-value roof rather than one with lower U-value). The larger the roof area, the better is the cooling effect. The maximum requirement of water per day for a place like Jodhpur is about 14.0 kg per square meter of roof area cooled. Spraying of water is preferable to an open roof pond system. One may also consider of using a vaulted roof since it provides a larger surface area for heat loss compared to a flat roof.

b) Walls: In multi-storied buildings, walls and glazing account for most of the heat gain. It is estimated that they contribute to about 80% of the annual cooling load of such buildings. So, the control of heat gain through the walls by shading is an important consideration in building design. One can also use a wall with low U-value to reduce the heat gain. However, the effectiveness of such walls depends on the building type. For example, in a non-conditioned building, autoclaved cellular concrete block wall is not recommended; whereas it is desirable in a conditioned building.

c) Fenestration: In hot and dry climates, minimizing the window area (in terms of glazing) can definitely lead to lower indoor temperatures. It is found that providing a glazing size of 10% of the floor area gives better performance than that of 20%. More windows should be provided in the north facade of the building as compared to the east, west and south as it receives lesser radiation during the year. All openings should be protected from the sun by using external shading devices such as chajjas and fins. Moveable shading

FIGURE 17: ROOF FORM