We design solar carports, and have run into an issue that has been causing some issues at particularly short spans.
According to ASCE7-16 Figure 30.7-1, we are allowed to interpolate between roof angle but there is no mention of interpolation for effective wind area. On many similar figures in Chatper 30, figures are provided that specifically do allow for linear interpolation (for example, Figure 30.6-2) but this one seems to only represent a stepped function with hard cutoffs. This can result in a slightly shorter purlin being designed for significantly higher pressures (and therefore higher moments and shears) which would require a heavier design than its slightly longer counterpart. I do not think this is the intent of the code, but I cannot find an exception listed to support that.
Please advise whether linear interpolation (or any other style of interpolation) is acceptable in this case, or if any clarifications or errata have been issued to address this.