Gutters on a slippery roof

[Prestressed Guy]

Are gutters installed on a building with a metal roof considered an “obstruction” on a slippery roof and negate the reduction of Cs allowed in ASCE-7 figure 7-2?

 

[dhengr]

Gutters probably aren’t exactly the ‘obstructions on a slippery roof’ intended in ASCE-7, but they will tend to act that way at the eaves. And, they are certainly prone to being ripped off the roof by sliding snow and ice. I don’t have the latest ed. of ASCE-7, but I think I would take the reduction on most of the roof structure, except near the eaves. Then the second winter you can take the reduction on the whole roof. Maybe some of the gutter cap (gutter helmet?) systems solve some of this problem, check with those manufacturers, and their warranties.

 

[BAretired]

I would think that the snow would start sliding on a slippery roof and would fly right over the gutter, removing all snow in its path.

BA

 

[Prestressed Guy]

Part of the reason that I am asking is that you are required to put snow fences on a standing seam metal roofs over exit doorways to protect from sliding snow. It seems to take very little restriction to stop the snow from sliding. The project has a ground snow load of 105 psf. Roof snow is 75 psf and with a slippery roof it drops to 50 psf. That is a big reduction. I would hate to use it and find out that the snow didn’t slide. :>O

It is safe to assume that this reduction is not applicable to any valleys.

 

[BAretired]

Gutters do get torn off from sliding snow according to the attached link, so I think it is correct to say they act as a deterrant to sliding. You will need a snow fence to prevent damage to the gutters.

http://www.graceguttering.com/Blog/Blogger/2011/01/03/c0e6f78b-d690-4ecb-bfa3-a166b63d9596.aspx

BA

 

[ajk1]

Presunmably you have to design the roof deck and beams for the weight of snow that piles up behind the snow guard. Also don't use a low height reinforced masonry parapet as a snow guard. The sliding snow will zoom out over the top of it and form a frozen mass that cantilevers out beyond and then suddenly breaks off when things warm up! Sliding snow can also rip out roof projections such as vents and chimneys etc. These slippery roofs, whether steel deck or single ply roofing, can be an issue if these things are not accounted for in design.