SpecTopics: Adjustments Between ASCE 7-16 and ASCE 7-22

As the building code evolves, so does the ASCE 7. Developed by American Society of Civil Engineers, the most commonly used ASCE 7 version in the U.S. at this time is the ASCE 7-2016. This version introduced an elevation of sea level factor, increased the internal pressure coefficient, breaking up Risk Category III and IV into a total of four sets of ultimate wind maps, and adjusted the roof areas to four zones for buildings that are 60 feet or less with slopes 7° or less.

ASCE 7-2016

(ASD) Velocity Pressure qz = (0.00256)(Kz)(Kzt) (Ke) (Kd)(V²)(0.6)

Kz = Velocity Pressure Coefficient = (based on roof height and ground exposure)
Kzt = Velocity Pressure Coefficient (wind speed-up over hills and escarpments) = 1
Ke = Ground Elevation Factor
Kd = Wind Directionality = 0.85
V = Vult Basic Wind Speed = (from ASCE 7-16 Risk Category I, II, III, and IV Map Sets)
0.6 = Allowable Stress Factor

Design Pressures of Zone 1’, Zone 1, Zone 2, and Zone 3 (Effective Area 10 square feet)

Roof Zones	Zone 1’	Zone 1	Zone 2	Zone 3
Roof Zones (-psf)	(qz)[(GCp)-(GCpi)]	(qz)[(GCp)-(GCpi)]	(qz)[(GCp)-(GCpi)]	(qz)[(GCp)-(GCpi)]
GCp (60‑ft or less in height with a slope of 7° or less)	-0.9	-1.7	-2.3	-3.2
GCpi (Enclosed)	0.18	0.18	0.18	0.18
GCpi (Partially Enclosed)	0.55	0.55	0.55	0.55

qz = (ASD) Velocity Pressure
GCp = External Pressure Coefficient
GCpi = Internal Pressure Coefficient

With the publication of the 2024 International Building Code (IBC), the ASCE 7-2022 was adopted with its adjustments. Some changes will eventually be required after governing bodies ratify and accept this document. The adjustments that have been made are as follows:

• Kd factor (Wind Directionality) has been removed from the Velocity Pressure calculations to the Design Pressure calculation for the Roof Zones
• Added a Chapter 32 for Tornado Loads

ASCE 7-2022: Wind Loads

(ASD) Velocity Pressure qz = (0.00256)(Kz)(Kzt)(Ke)(Kd) (V²)(0.6)

Kz = Velocity Pressure Coefficient = (based on roof height and ground exposure)
Kzt = Velocity Pressure Coefficient (wind speed-up over hills and escarpments) = 1
Ke = Ground Elevation Factor
V = Vult Wind Speed = (from ASCE 7-22 Risk Category Maps)
0.6 = Allowable Stress Factor

Design Pressures of Zone 1’, Zone 1, Zone 2, and Zone 3 (Effective Area 10 square feet)

Roof Zones	Zone 1’	Zone 1	Zone 2	Zone 3
Roof Zones (-psf)	(qz) x Kd x [(GCp)-(GCpi)]	(qz) x Kd x [(GCp)-(GCpi)]	(qz) x Kd x [(GCp)-(GCpi)]	(qz) x Kd x [(GCp)-(GCpi)]
GCp (60‑ft or less in height with a slope of 7° or less)	-0.9	-1.7	-2.3	-3.2
GCpi (Enclosed)	0.18	0.18	0.18	0.18
GCpi (Partially Enclosed)	0.55	0.55	0.55	0.55

qz = (ASD) Velocity Pressure
Kd = Wind Directionality = 0.85
GCp = External Pressure Coefficient
GCpi = External Pressure Coefficient

ASCE 7-2022: Chapter 32 Tornado Loads

The following calculations are limited to Risk Category III or IV type buildings, must be in a tornado-prone region, tornado local ultimate winds are greater than 60-mph, tornado local ultimate winds are greater than based on the following formula’s exposure categories.

 

Exposure	Formula
B	Vt ≥ 0.5 x V
C	Vt ≥ 0.6 x V
D	Vt ≥ 0.67 x V

Example

Tornado Load Calculations

(ASD) Velocity Pressure qztor = (0.00256)(Kztor)(Ke)(Vt²)(0.6)

Kztor = Velocity Pressure Coefficient (Tornado) = (based on roof height)
Ke = Ground Elevation Factor
Vt = Vult Tornado Wind Speed = (from ASCE 7-22 Tornado Maps – based on Risk Category III or IV and effective plan area)
0.6 = Allowable Stress Factor

Design Pressures of Zone 1’, Zone 1, Zone 2, and Zone 3 (Effective Area 10 square feet)

Roof Zones	Zone 1’	Zone 1	Zone 2	Zone 3
Roof Zones (-psf)	(qz) x [(Kdt x Kvt x GCp)-(GCpiT)]	(qz) x [(Kdt x Kvt x GCp)-(GCpiT)]	(qz) x [(Kdt x Kvt x GCp)-(GCpiT)]	(qz) x [(Kdt x Kvt x GCp)-(GCpiT)]
GCp (60‑ft or less in height with a slope of 7° or less)	-0.9	-1.7	-2.3	-3.2
GCpiT (Partially Enclosed)	0.55	0.55	0.55	0.55

qztor = (ASD) Velocity Pressure (Tornado)
Kd = Tornado Directionality (Essential Facilities) = 1
Kvt = Tornado Pressure Coefficient Adjustment Factor for Vertical Winds

Roof Zones	Zone 1’	Zone 1	Zone 2	Zone 3
Kvt Coefficient	1	1.2	1.05	1.05

GCp = External Pressure Coefficient
GCpiT = Tornado External Pressure Coefficient

Additional SpecTopics posts are available on the subject of ASCE 7 and can be found on the SpecTopics page.

An ASCE 7 calculator tool is also available on the Carlisle SynTec Systems website.

Contact Brian Chamberlain at [email protected] with further questions.