Mechanical Equipment Wind Pressure Calculator

Rooftop equipment?
Project in Miami-Dade or Broward (HVHZ)?
Equipment dimensions

Look up the wind speed on the ASCE Hazard Tool.

How to use it

Review the references and results to make sure this methodology aligns with your project’s requirements, then:

  1. Enter the equipment model number, if you want it on the printout.
  2. Choose whether the equipment is on a roof.
    • If yes: choose whether the project is in Miami-Dade or Broward County, Florida’s High-Velocity Hurricane Zone (HVHZ), where rooftop units installed on stands have minimum clearance requirements below the equipment for maintenance, then enter the clearance below the equipment or the curb height (in) and the roof height (ft).
    • If no: choose wall-mounted or slab-mounted at grade, and enter the height to the bottom of the equipment (ft); enter 0 for slab-mounted equipment.
  3. Enter the equipment length, depth and height (in), from the manufacturer’s data.
  4. Choose the risk category and the exposure category, and enter the ultimate wind speed (mph). The ASCE Hazard Tool gives the ASCE 7-22 wind speed for an address and risk category.
  5. The lateral and uplift pressures appear in the results and update as you type. Print the page for a record of the inputs and results.

Design wind pressures (ASD)

Enter the clearance below the equipment.

ASCE 7-22, Chapters 26 and 29. Results are not valid unless verified, signed and sealed by a registered engineer.

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This mechanical equipment wind pressure calculator calculates the lateral and uplift pressures on mechanical equipment installed on rooftops, on walls or on slabs. It uses the ASCE 7-22 wind pressure methodology and equations, and takes into account the building height, exposure category, equipment location and wind speed. Whether you are an engineer, architect or contractor, it can help you determine the wind loads on equipment.

Methodology

The calculator follows ASCE 7-22, Chapters 26 and 29 (Chapter 29: Wind Loads on Building Appurtenances and Other Structures), at allowable stress design (ASD) level.

Height of the equipment

  • Rooftop: z = roof height + (clearance + equipment height) / 12 [ft]
  • Slab or wall: z = height to bottom of equipment + equipment height / 12 [ft]

For rooftop equipment ASCE 7-22 evaluates the velocity pressure at the building's mean roof height. The top of the equipment is at or above it, so taking z there is conservative.

Velocity pressure exposure coefficient (Table 26.10-1), with z taken as no less than 15 ft:

Kz = 2.41 × (z / zg)2/α, where zg = 3,280, 2,460 or 1,935 ft and α = 7.5, 9.8 or 11.5 for exposure B, C or D (Table 26.11-1).

Velocity pressure (26.10.2):

qz = 0.00256 × Kz × Kzt × Ke × V² [psf], with Kzt = 1 (26.8.2) and Ke = 1 (26.9). In ASCE 7-22 the directionality factor Kd is no longer part of qz; it is applied in the force equations below.

Design pressures (29.4.1, Equations 29.4-2 and 29.4-3, with Kd = 0.85 from Table 26.6-1 and the 0.6 ASD load factor of 2.4.1):

  • Lateral wind pressure = ± qz × Kd × GCr × 0.6, with GCr = 1.9
  • Uplift wind pressure = qz × Kd × GCr × 0.6, with GCr = 1.5

These are the largest GCr values, for equipment that is small next to the building. Section 29.4.1 lets them fall linearly toward 1.0 as the equipment's area grows toward that of the building's face or roof; the calculator does not take that reduction, which is conservative.

HVHZ clearance. For rooftop equipment in the High-Velocity Hurricane Zone (Miami-Dade and Broward counties), the minimum clearance under the equipment depends on its width (2023 Florida Building Code, Building, Table 1522.3). The calculator uses the longer plan dimension as the width, the conservative reading: 14 in for equipment up to 24 in wide, 18 in for 25 to 36 in, 24 in for 37 to 48 in, 30 in for 49 to 60 in, and 48 in for 61 in and wider. A width that falls between two rows takes the higher clearance.

The calculator flags equipment that is two or more times as long as it is tall, a proportion outside the range this calculation was set up for; have your engineer check those results.

Slab- and wall-mounted equipment. Section 29.4.1 is written for rooftop equipment. The calculator applies the same GCr factors (1.9 lateral, 1.5 uplift) to equipment on a slab or a wall, which is conservative for equipment that is not on a roof.

Risk category. The risk category sets which wind speed map applies. It changes the result only through the wind speed you enter.

Tornado loads. ASCE 7-22 adds tornado loads (Chapter 32) for Risk Category III and IV buildings in the tornado-prone region. This calculator covers the ordinary wind loads of Chapters 26 and 29 only.

Compared with ASCE 7-16. Moving Kd out of qz does not change the pressures. The new Kz constants change them by: Exposure B, 0.3% to 5% lower (the most on tall buildings); Exposure C, within about 1%; Exposure D, 0.5% higher.

Florida Building Code note

Per the 2023 Florida Building Code, Section 1609.1.1, Determination of Wind Loads:

"Exposed mechanical equipment or appliances fastened to a roof or installed on the ground in compliance with the code using rated stands, platforms, curbs, slabs, walls, or other means are deemed to comply with the wind resistance requirements of the 2007 Florida Building Code, as amended. Further support or enclosure of such mechanical equipment or appliances is not required by a state or local official having authority to enforce the Florida Building Code."

Results are not valid unless verified, signed and sealed by a registered engineer. Adicot, Inc. makes no guarantees to the accuracy of these results.

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