The correct answer is: C. Both (A) and (B).
The external wind pressure acting on a roof depends on the degree of permeability of the roof and the slope of the roof.
The degree of permeability of the roof is the measure of how easily air can flow through the roof. A more permeable roof will allow more air to flow through it, which will reduce the amount of wind pressure acting on the roof. A less permeable roof will allow less air to flow through it, which will increase the amount of wind pressure acting on the roof.
The slope of the roof is the angle of the roof relative to the horizontal. A steeper roof will have more wind pressure acting on it than a less steep roof. This is because the wind will be able to flow more easily over a less steep roof, which will reduce the amount of wind pressure acting on the roof.
The following are some additional details about the factors that affect the external wind pressure acting on a roof:
- The height of the roof: The higher the roof, the more wind pressure will act on it. This is because the wind will have more time to build up speed as it travels up the roof, which will increase the amount of wind pressure acting on the roof.
- The shape of the roof: The shape of the roof can also affect the amount of wind pressure acting on it. A roof that is more streamlined will have less wind pressure acting on it than a roof that is more angular. This is because the wind will be able to flow more easily over a streamlined roof, which will reduce the amount of wind pressure acting on the roof.
- The location of the roof: The location of the roof can also affect the amount of wind pressure acting on it. A roof that is located in a windy area will have more wind pressure acting on it than a roof that is located in a less windy area. This is because the wind will be stronger in a windy area, which will increase the amount of wind pressure acting on the roof.
- The type of roof: The type of roof can also affect the amount of wind pressure acting on it. A roof that is made of a more rigid material will have less wind pressure acting on it than a roof that is made of a less rigid material. This is because the wind will be able to deform a less rigid roof more easily, which will increase the amount of wind pressure acting on the roof.