Wind on Large Overhangs 1

[dgboley]

The code doesn’t really go into depth on wind on large overhangs. We have a 30’-0” overhang and I need advice on how to approach wind loading and uplift on the overhang. I have done a roof components and cladding run but I am not sure if that is accurate. Would we use the same component and cladding load for zones 1, 2, and 3 on both the underside and the top side?

Thank you for your time,
Dennis Boley

 

[ztengguy]

30' overhang? I doubt wind will control.

 

[dgboley]

The worst case component and cladding wind load is 45psf, while the dead load is 10psf. We are looking at the design of the soffit structure.

 

[Ron]

For an overhang that large, I would just consider it to be a cantilevered structure having its own edge and interior zones.

 

[dgboley]

So we should treat it as a partially enclosed structure with one wall and a roof? Running a roof, components and cladding load for the top of the overhang and use the MWFR system internal pressure for the underside?

 

[SAIL3]

there really is not enough info on the structure to give an informed judgement on what to use....IMO the 30' overhang would drive my decision to use -/+ 2.0 form factor on the entire area....one cannot guarantee that the wind velocity vector will be horizontal..

 

[a2mfk]

Something I have pondered my entire career. You would think since every retail box shopping center in the US now gets built with a rather large canopy along the front of the building, that this would be something that would come up more often in conversation. What about porte-cochere structures in front of hotels and home improvement stores that are attached to the main building? Are these overhangs or open structures or a bit of both??

In the absence of better guidance from ASCE 7 on this subject, I have always defaulted to the most conservative wind loading- overhang pressures. I think the portion of the roof overhang adjacent to the building will have the highest underside (upward) pressure on the ceiling/soffit because the wind is hitting the wall of the structure and then going upwards and there are localized high pressure zones. However, as you get further away from the building wall this pressure likely diminishes. But how much? I think at some point it transitions into behaving more like an open structure with very little upward pressure on the ceiling/soffit. I have heard some suggestions like out 10-15 feet you could switch over to open roof loading pressures. I would not argue with this logic either, and may have taken similar approaches in the past. Or maybe I am way off here...

 

[UcfSE]

Is this an overhang of the type that ASCE 7-10 figure 30.7-2 "Application of Overhang Wind Loads" would apply?