Structure on top of roof

[xez]

Hello,

Let's say I have a 100 ft x 100 ft x 40 ft building. On top of this building at the center, I have a 40 ft x 40 ft x 30 ft (L x W x H) structure. When calculating the wind loads, would the structure on the roof be considered a 70 ft elevation or 30 ft elevation? Does the answer change if the rooftop structure is located so that the walls are a few feet away from the edge of the main building?

Thanks.

 

[Shotzie]

I would assume that you would take the full height of the structure (70 ft) as I believe those factors are related to the wind speed increasing as you have less drag due to ground obstructions.

 

[xez]

Thank you Shotzie. That was my assumption as well, but didn't know if I was being conservative since it is a smaller structure compared to the main building.