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Residential Design Pressure

Frequently Asked Questions

Exposure

Exposure B

For buildings with a mean roof height of less than or equal to 30 feet (9144 mm), Exposure B shall apply where the ground surface roughness, as defined by Surface Roughness B, prevails in the upwind direction for a distance of at least 1,500 feet (457 m). For buildings with a mean roof height greater than 30 feet (9144 mm), Exposure B shall apply where Surface Roughness B prevails in the upwind direction for a distance of at least 2,600 feet (792 m) or 20 times the height of the building, whichever is greater.

Exposure C

Exposure C shall apply for all cases where Exposure B or D does not apply.

Exposure D

Exposure D shall apply where the ground surface roughness, as defined by Surface Roughness D, prevails in the upwind direction for a distance of at least 5,000 feet (1524 m) or 20 times the height of the building, whichever is greater. Exposure D shall also apply where the ground surface roughness immediately upwind of the site is B or C, and the site is within a distance of 600 feet (183 m) or 20 times the building height, whichever is greater, from an Exposure D condition as defined in the previous sentence.

Risk Category

This is the risk associated with the use of the building.

RISK CATEGORY
NATURE OF OCCUPANCY
I
 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.
  • Screen enclosures.
II
 Buildings and other structures except those listed in Risk Categories I, III and IV.
III
 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 whose primary occupancy is public assembly with an occupant load greater than 300.
  • Buildings and other structures containing Group E occupancies with an occupant load greater than 250.
  • Buildings and other structures containing educational occupancies for students above the 12th grade with an occupant load greater than 500.
  • Group I-2 occupancies with an occupant load of 50 or more resident care recipients but not having surgery or emergency treatment facilities.
  • Group I-3 occupancies.
  • Any other occupancy with an occupant load greater than 5,000.a
  • Power-generating stations, water treatment facilities for potable water, wastewater treatment facilities and other public utility facilities not included in Risk Category IV.
  • Buildings and other structures not included in Risk Category IV containing quantities of toxic or explosive materials that:
    • Exceed maximum allowable quantities per control area as given in Table 307.1(1) or 307.1(2) or per outdoor control area in accordance with the Florida Fire Prevention Code; and
    • Are sufficient to pose a threat to the public if released.b
IV
 Buildings and other structures designated as essential facilities, including but not limited to:
  • Group I-2 occupancies 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, communications and operations centers and other facilities required for emergency response.
  • Power-generating stations and other public utility facilities required as emergency backup facilities for Risk Category IV structures.
  • Buildings and other structures containing quantities of highly toxic materials that:
    • Exceed maximum allowable quantities per control area as given in Table 307.1(2) or per outdoor control area in accordance with the Florida Fire Prevention Code; and
    • Are sufficient to pose a threat to the public if released.b
  • Aviation control towers, air traffic control centers and emergency aircraft hangars.
  • Buildings and other structures having critical national defense functions.
  • Water storage facilities and pump structures required to maintain water pressure for fire suppression.
How to Determine the Zone 4 or 5 and Explanation for End Wall

               To determine the design pressures, you will need to enter the opening size and determine if the opening is in zone 4 or zone 5. The diagram below shows each zone, the dimension “a” is the end wall displayed below, so from the corner and form a distance of “a” it falls under zone 5.
If only a portion of the opening is within this area, assume zone 5.

Determine zone 4 or 5
Height above the ground

             Height from ground level to the middle of the roof height.

Height above the ground for a house
Wind load

            Ultimate wind speed, this is the speed design, it is determined by the building code.

wind speed wind load florida
icon About
Exposure represents the adjustments due the characteristics of the terrain surrounding the building.

Exposure B.For buildings with a mean roof height of less than or equal to 30 feet (9144 mm), Exposure B shall apply where the ground surface roughness, as defined by Surface Roughness B, prevails in the upwind direction for a distance of at least 1,500 feet (457 m). For buildings with a mean roof height greater than 30 feet (9144 mm), Exposure B shall apply where Surface Roughness B prevails in the upwind direction for a distance of at least 2,600 feet (792 m) or 20 times the height of the building, whichever is greater.

Exposure C.Exposure C shall apply for all cases where Exposure B or D does not apply.

Exposure D.Exposure D shall apply where the ground surface roughness, as defined by Surface Roughness D, prevails in the upwind direction for a distance of at least 5,000 feet (1524 m) or 20 times the height of the building, whichever is greater. Exposure D shall also apply where the ground surface roughness immediately upwind of the site is B or C, and the site is within a distance of 600 feet (183 m) or 20 times the building height, whichever is greater, from an Exposure D condition as defined in the previous sentence.

 

 
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