While one of the most important roles of roofing is to fight the weather, they also have significant effects on the aesthetic, cost and durability of a building. In Roof Cladding, factors such as rainfall, wind speed, height of building and walking weight on roofs (arising out of maintenance) have considerable effect on design of roof slope, supporting structures and spacing between Purlins  (Figure-1) . Design parameters for Wall Cladding is simple and straightforward compared to Roof Cladding. The main consideration in the design is spacing between the supports, known as “Side Girt” (equivalent of
Purlins used in Roof Cladding). Wind speed and thickness of sheets play major role in arriving at the spacing between Side Girt.

 Slope :

Slope is a major component of roof design. In absence of adequate roof slope, there is danger of water accumulation, which can lead to leakage and reduced sheet life. Most commonly used roof slopes in India are 1 in 4 (14º) and 1 in 3 (18º)  (Figure 2 & 3). However, various other slopes can be used depending upon the intensity of rainfall and wind force. In case of sinusoidal profiles, it is recommended that one should not go below slope of 1 in 12 (5º). It is important to use sealants at the end lap of sheets in case roof slope is below 5º.

 Overhang :

Overhang in Roof Cladding is important from the angle of complete weather-proofing of the building. While “End Overhang” maintained at the “Eave End” (Gutter end) of the roof facilitates proper drainage of water without drenching the inside of building from its front, the “Side Overhang” makes sure the rain water does not enter the building from sides  (Figure-4) . Overhangs are recommended below as per good engineering practice.

 Joints on the sheets :

Joints on the roofing sheets, also known as 'Laps', are critical in fabrication of leakage proof roofs. Joints on the side of the roofing sheet (along sheet length) are known as “Side Lap”  (Figure-5)  while joint at the end of the sheet (along sheet width) is known as “End Lap”  (Figure-6).  Slope of the roof plays a major role in deciding the area of laps.