2018 IBC (ASCE 7-16) vs 2018 IRC Wind Speed Issues

[JoshPE]

Hello,


I work in the residential solar field and complete structural analysis reports for solar projects. I've noticed an issue with jurisdictions that have began to adopt the 2018 IBC. I will submit my calculations using ASCE 7-16, which utilizes the new "Basic" wind speeds that tend to be lower than the older Vult wind speeds. Many jurisdictions will kick back these calculations and state that they require a higher wind speed, which is essentially the Vult wind speed that is still referenced in the 2018 IRC. Does anyone have any explanation for this? I'm not sure why the 2018 IRC references different wind speeds than the 2018 IBC. I've had the same issue with jurisdictions in NV, AZ, and CO so far. I'm wondering if I'm missing something or if it's just going to take time for jurisdictions to get on the same page.

Thanks for the help!

Josh

 

[r13]

If IRC still in force at those jurisdictions, use the stricter one.

 

[phamENG]

Are you sealing these calculations/reports? Also, are the houses these are going onto being designed by an engineer or using prescriptive code requirements?

If everything is being engineered and sealed, you can claim the IRC section 301 exception that it is being designed in accordance with standard engineering practice per the requirements of the IBC. That messes up some jurisdictions - I've seen where pulling that puts the house on the commercial plan reviewer's desk because the residential plan reviewer only knows the IRC. But it would be a means of using your standard. The AHJ does, of course, have the authority to say too bad and require it anyway.

Given that, how much of a change is it? (my jurisdiction just adopted IBC 2015, so I don't need to worry about ASCE 7-16 for a while.) Is it going to drastically change your connections or make your solar client less competitive? If not, probably easier to just use the higher wind speed and keep going.

 

[r13]

Always check local requirement before design. I remember some jurisdiction/agency adopting code without accepting entirety. At the end, they are the boss.