What does category mean and how do I determine it?
Category refers to the occupancy category which designates how the structure is intended to be used and affects the required design loads for the building. These loads include flood, wind, snow, earthquake and ice.
Category 1: Low Hazard to Human Life
Buildings and other structures that represent a low hazard to human life in the event of failure including, but not limited to:
- Agricultural facilities
- Certain temporary facilities
- Minor storage facilities
Category 2: Other
All buildings and other structures except those listed in Categories 1, 3, and 4.
Category 3: Substantial Hazard to Human Life
Buildings and other structures that represent a substantial hazard to human life in the event of failure including, but not limited to:
- Buildings and other structures where more than 300 people congregate in one area
- Buildings and other structures with day care facilities with capacity greater than 150
- Buildings and other structures with elementary school or secondary school facilities with capacity greater than 250
- Buildings and other structures with a capacity greater than 500 for colleges or adult education facilities
- Health care facilities with a capacity of 50 or more resident patients but not having surgery or emergency treatment facilities
- Jails and detention facilities
- Power generating stations and other public utility facilities not included in Category 4
- Buildings and other structures not included in Category 4 (including, but not limited to, facilities that manufacture, process, handle, store, use, or dispose of such substances as hazardous fuels, hazardous chemicals, hazardous waste, or explosives) containing sufficient quantities of hazardous materials to be dangerous to the public if released.
- Buildings and other structures containing hazardous materials shall be eligible for classification as Category 2 structures if it can be demonstrated to the satisfaction of the authority having jurisdiction by a hazard assessment as described in Section 1.5.2 that a release of the hazardous material does not pose a threat to the public.
Category 4: Facility Essential in Emergencies
Buildings and other structures designated as essential facilities including, but not limited to:
- Hospitals and other health care facilities having surgery or emergency treatment facilities
- Fire, rescue, ambulance, and police stations and emergency vehicle garages
- Designated earthquake, hurricane, or other emergency shelters
- Designated emergency preparedness, communication, and operation centers and other facilities required for emergency response
- Power generating stations and other public utility facilities required in an emergency
- Ancillary structures (including, but not limited to, communication towers, fuel storage tanks, cooling towers, electrical substation structures, fire water storage tanks or other structures housing or supporting water, or other fire-suppression material or equipment) required for operation of Category 4 structures during an emergency
- Aviation control towers, air traffic control centers, and emergency aircraft hangars
- Water storage facilities and pump structures required to maintain water pressure for fire suppression
- Buildings and other structures having critical national defense functions
- Buildings and other structures (including, but not limited to, facilities that manufacture, process, handle, store, use, or dispose of such substances as hazardous fuels, hazardous chemicals, hazardous waste, or explosives) containing extremely hazardous materials where the quantity of the material exceeds a threshold quantity established by the authority having jurisdiction.
- Buildings and other structures containing extremely hazardous materials shall be eligible for classification as Category 2 structures if it can be demonstrated to the satisfaction of the authority having jurisdiction by a hazard assessment as described in Section 1.5.2 that a release of the extremely hazardous material does not pose a threat to the public. This reduced classification shall not be permitted if the buildings or other structures also function as essential facilities.
How do you determine the exposure types?
Exposure category is available from ASCE 7-16 which is produced by The American Society of Civil Engineers and is also available in Chapter 16 of the International Building Code. The exposure category is based upon ground surface roughness, which is determined from the topography, vegetation, and existing structures.
B: Urban or Suburban
Area with numerous closely-spaced obstructions having the size of single-family dwellings or larger. For all structures shown, terrain representative or surface roughness Category B extends more than ten times the height of the structure or 800 meters, whichever is greater, in the upwind direction.
C: Scattered Obstruction
Open terrain with scattered obstructions having heights generally less than 30 feet for most wind directions. All one-story structures with a mean roof height less than 30 feet in the photograph are less than 1500 feet or ten times the height of the structure, whichever is greater, from an open field which prevents the use of Exposure B. Also includes shoreline in hurricane-prone regions.
D: Open Water for One Mile or More
A building at the shoreline (excluding shorelines in hurricane-prone regions) with wind flowing over open water for a distance of at least one mile. Shorelines in Exposure D include inland waterways, the Great Lakes, and coastal areas of California, Oregon, Washington and Alaska.
Source: https://www.spri.org/faq/ and https://www.pieglobal.com/press/determining-wind-loads-in-relation-to-building-design-and-construction/
What are horizontal and vertical design pressures?
Horizontal: Acting outward from the building edge
Vertical: Acting upward at the building edge
Edge System Resistance
Roof edge systems may be selected from manufacturers who certify certain minimum performance to meet design requirements, based upon testing. Any roof edge system may be used provided that it is tested and certified by an independent testing laboratory to meet the wind design requirements.
The vertical face of an edge flashing (gravel stop) shall be tested according to Test RE-2 and provide a strength that meets or exceeds the required horizontal design pressure. The test shall be applicable to systems with exposed horizontal components less than 4 in (100 mm) as detailed in the RE-2 Test Method; otherwise Test RE-3 is applicable.
The vertical and horizontal faces of copings (and like roof edge systems) shall be tested according to Test RE-3 and provide a strength that meets or exceeds the horizontal and vertical pressures required.
The roof edge system, when used for securing dependently terminated roofing systems, shall be tested according to Test RE-1 to provide a strength that meets ANSI/SPRI/FM 4435/ES-1.