Snow Drift Between Building and Sign

[JRR66]

I have a design problem where a new decorative wall is being placed in front of an existing building.

To prevent snow from drifting on the existing roof, there was a thought about pulling the wall off and away from the existing building and providing a gap. But with only a 1' gap between the building and wall, I am concerned drifting could still occur.

Does anyone have any insight into this problem or know of any stipulations in ASCE 7-16 that address this issue. Does anyone know of any articles about this situation that they can recommend?

I have attached a rough sketch depicting the design problem. The building is located on Long Island NY with a Pg = 30psf the roof is flat.

Thanks,
John

 

[flight7]

The commentary to ASCE 7-16 mentions that when a new structure is built within 20 feet of an existing structure, drifting possibilities should be investigated. I would imagine a drift forming as if the gap is solid, then remove the snow directly above the gap. But in your case where there is only a one-foot gap I would assume that the snow does bridge over that gap, although the additional weight is small.

 

[JRR66]

flight7,

Thank you for the information I will review the ASCE commentary. I agree with your thoughts on the gap being bridged.

 

[Rabbit12]

For your condition you're obviously concerned about a windward drift. Without snow bridging that opening I doubt you'll see much of a drift. Under ideal conditions it's possible you could see a bridge there, but wouldn't be a common occurrence.

If you can move the sign a bit further away that would solve that problem. I'd think 3-4' would be enough of a gap to prevent any chance of bridging. Certainly wouldn't need to be 20'. I believe that 20' requirement applies to leeward drifting.

 

[JRR66]

Rabbit12,

Thanks for the feedback.

Yes, Winward drift is the concern I should have mentioned that.

The 20' requirement seems to apply for both windward or leeward. However, my situation does not seem to be addressed.

Pulling it off the building a bit more may be the way to go to avoid drift.

 

[Rabbit12]

I have trouble seeing how a leeward drift can develop with a 20' gap. Windward sure.

Maybe there is some research towards that 20' number for leeward drifts. If so I'd like to see it.

 

[dik]

a 1' gap would have little or no effect...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Rabbit12]

Dik, can you explain that a littler further?

 

[HTURKAK]

Pulling the wall will help ...that is true.. but better pull down the decorative wall ... What is the reason for the H difference 56'' ?..

I think the following doc. is insightful to get the concept.

 

[r13]

JRR66,

Looks like this should help (image excerpted from p.15 of doc provided by HTURKAK).

 

[JStructsteel]

How wide is the sign?