Regarding ASCE 7-16 & the 2020 Florida Building Code (FBC)
Section 1609.1.1 and Chapter 35 of the 2020 FBC refer to ASCE 7-16 as the governing code for loading requirements on most rooftop structures*. *Section 1609.5 of the 2020 FBC lays out additional requirements for roof decks, shingles, and roof tiles
ASCE 7-16 again revised the design requirements.
- Addition of a ground elevation factor Ke. This factor adjusts for air density depending on site location, presenting the possibility for wind pressure reductions over ASCE 7-16 as ground elevation above sea level increases. For more information, see ASCE 7-16: Table 26.9-1.
- New wind directionality factors, Kd:
- Rooftop Equipment are clarified to have a Kd of 0.85. In ASCE 7-10, rooftop equipment did not have their own Kd designation. Previously, Engineering Express had used a Kd of 0.90 under ASCE 7-10, grouping with Chimneys, Tanks, and Similar Structures. This 7-16 clarification resulted in a minor wind pressure reduction on our wind load calculations for rooftop equipment.
- Round and octagonal, axisymmetric chimneys, tanks, and similar structures now have a Kd of 1.0 instead of 0.95. Circular domes also carry a Kd of 1.0 under ASCE 7-16.
- For more information, see ASCE 7-16: Table 26.6-1.
- Building height requirement eliminated for wind pressure calculations on Rooftop Structures and Equipment. This cleans up a loophole in ASCE 7-10. In ASCE 7-10, uplift pressures were only required for rooftop structures and equipment for building heights with a mean roof height of 60 ft or less. For buildings greater than 60 ft tall, only lateral pressures were required. (See ASCE 7-10, Section 29.5.1). Under ASCE 7-16, it is clarified that lateral and uplift pressures are required on all* rooftop structures and equipment for buildings of any height. (*Solar panels have special wind pressure requirements – see next bullet).
- *Rooftop Solar Panels were given their own wind pressure calculation requirements, based on roof slope and panel array construction. Additions are extensive; it is recommended to consult ASCE 7-16 Sections 29.4.3 and 29.4.4 separately for full specifications.
More can be found on our FORCES Page, where you’ll find a helpful tool to determine wind pressures on rooftop equipment.
The loading requirement of “Rooftop Structures” was also revised in ASCE 7-10.
NOTE: For states other Florida: States that adhere to the latest edition of the International Building Code (IBC 2018) will also follow the new ASCE 7-16 requirements.
However, some states continue to operate under the older editions of the International Building Code (IBC 2012 & 2015). For IBC 2012 & 2015, the appropriate Reference Standard is ASCE 7-10. As such, ASCE 7-10 stipulations may still be applicable. The below sections provide a discussion of loading requirements for ASCE 7-10. For more information on which IBC edition is adopted by state as of January 2021, please visit: https://www.iccsafe.org/wp-content/uploads/Master-I-Code-Adoption-Chart-jan-2021.pdf
ASCE 7-10 Commentary
Essentially, buildings less than 60-ft still have the requirement that their wind load be multiplied by a GCr factor applied to the wind pressure that can be as high as 1.9. This has been in place since the 2007 version of the standard (ASCE 7-05). A new section, section 29.5.1, also requires that a GCr uplift factor as high as 1.5 be applied to the top of the rooftop structure in combination with the lateral force. It is also EXTREMELY IMPORTANT for Florida design professionals to note that the 2010 Florida Building Code requires an even higher GCr of 3.1 be utilized for buildings of all heights, not just buildings 60-ft or less. The uplift forces are also required to be in combination with the lateral forces for all buildings in Florida and for use with the International Building Code.
Per The 2014 FBC/IBC 1609.8 Rooftop Structures and Equipment:The lateral force on rooftop structures and equipment with Af less than (0.1Bh) located on buildings of all heights shall be determined from Equation 29.5-1 of ASCE 7 in which the value of GCf shall be taken as 3.1. GCf shall be permitted to be reduced linearly from 3.1 to 1.1 as the value of Af is increased from (0.1Bh) to (Bh). The value of G from Section 26.9 of ASCE 7 shall not be used. Additionally, a simultaneous uplift force shall be applied, given by Equation 29.5-1 of ASCE 7 in which GCf= 1.5 and Af is replaced by the horizontal projected area, Ar, of the rooftop structure or equipment. For the uplift force GCf shall be permitted to be reduced linearly from 1.5 to 1.0 as the value of Ar is increased from (0.1BL) to (BL).
Last Update: April 1, 2021