The map shown here provides Ultimate Design Wind Speeds for risk category 2 buildings. RC 2 covers what are generally regarded as “ordinary” structures. Risk Category takes into account occupancy and use-we’ll discuss that more in a bit. IBC 2015 considers four risk categories (RC) ranging from lowest to highest hazard to human health.

Figure 1 shows a map taken from IBC 2015. The location of a building determines the wind speed that is used to determine the uplift loads. Let’s discuss each of the six factors in more detail And who says complying with the bare minimum is the correct choice? However, some of these factors can be “in the eye of the beholder,” and a designer’s level of conservatism may come into play. Exposure should be easily determinable because it is based on a building’s relative location to adjacent surroundings. Location and applicable code are fixed, as are the buildings dimensions-length, width, and height.

It would appear that the factors for wind design are all fixed and not debatable, but there are presumptions made during the wind design of every roof. The uplift loads acting on a roof are influenced by a number of factors-geographic location, the local building code, dimensions, exposure, use and occupancy (aka risk factor), and type. Roofs need to resist the uplift loads acting on the roof. In the roofing industry, one of the most important aspects of roof system design is wind resistance.

Nscp 2015 wind load map