Key Terms Used In This Article For Reference:
Understanding Wall Zones 4 & 5
An analysis of wind pressure acting on a building component (window, door, etc.) is performed depending in part on what wind pressured zone it is in (see illustrations below).
Chapter 2411.1.8 of the Florida Building Code (HVHZ) permits Zone pressures that fall between two zones to be interpolated up to a maximum of 50% in zone 5, providing a documented interpretation of the code in a high-risk area. Use our ASCE 7 Zone Interpolator Calculator to interpolate your application. Certified results can be reviewed and provided for permit.
It is important to note that the intent of the code is a ‘lite’ of glass – If several units are mulled together with a structural break, each unit as well as the structural break shall be considered separately.
The interpretation of zones should be left to a licensed professional engineer when in doubt. Otherwise, the most critical wall zone 5 is recommended to be used.
Below is a video that helps illustrate how the zone 5 vortexes form and how to better understand the theory of the zone 5 effect. Keep in mind that the wind has to come from an opposing direction (all structures are analyzed with wind approaching from all angles), the most critical of which will create turbulent effects in the video.
Helpful ASCE 7 Wall Wind Zone Illustrations
Additionally per AAMA TIR A-15-14, wall zones 4 & 5 can be further explained as:
170 Degrees: Unobstructed exterior corner is considered Zone 5 if the angle < 170 degrees open as shown
Note on this designation: ASCE 7-16/22 uses a 135-degree designation instead of 170 degrees, explaining in Figure C30-2 (below) that roof zone 3 and wall zone 5 need not be applied at that corner. The difference refers to engineering judgment of ‘building corner discontinuity’ and ‘wind flow separation’. This is also a possible solution that is for consideration at the discretion of the reviewing design professional. The more critical has been illustrated here for purposes of providing a more generalized design solution.
(Updated 2-2022 from user feedback).
ASCE 7 also published a commentary that explains wall and roof zone areas. From the below figure, more information is shown to describe further how zones 4 and 5 are determined:
Watch this video to help better explain how end-zone 5 vortexes form
Note: Roof wind zones follow a similar theory and are not covered in this article or knowledge base to date.
Last Update: October 4, 2024
