Snow guards (Sno-Fence) on large metal building - worth it?

[Jc67roch]

We have constructed a large PEMB, 375 ft long by 120 wide 2:12 roof pitch with metal roofing. The location is upstate NY with 40 psf ground snow load. It is a highway garage structure, heated, with multiple large overhead doors and man doors. I have researched and found conflicting opinions on whether to install sno-guards on the roof to prevent or limit the amount of snow falling off the roof. We are looking at installing Alpine Sno-Fence S-5! only at the locations over the doors. They clip to the metal roof ribs and are pretty sturdy. But the question is with this large a metal roof is it even logical to try to retain that snow on the roof? This things might just get ripped off. Are snow retention systems usually provided on this type and scale of structure?

Roof crickets weren't really an option either due to the large expanse of doors (see sketch).

I am also looking for information on steel or aluminum "angles" bolted to the roof (ribs) that would deflect the sliding snow to the sides of the openings. This may still be a problem at the large row of overhead doors. But does anyone have a manufacturer or design for this type of item that they can recommend?

Does any one have other recommendations for protecting trucks and people from falling snow at these door locations?

Thanks.

 

[OHIOMatt]

Before you install snow guards, you should verify that the roof would have capacity for it. A 2:12 pitch with metal roof panels may have been designed as unobstructed and slippery. This allows the snow to fall off, thus reducing the required design load. I personally would never use that provision of the code for a structure of this type, but the PEMB company may have.

 

[MiketheEngineer]

I would prefer the roof sheds as much snow as possilbe and as quick as possible. HOWEVER - where you have access that can be a bit dangerous. I would strongly suggest them at doors, entries, etc.

 

[msquared48]

I would seriously question whether a 2:12 pitch on a metal roof would shed snow at all.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[TonyES]

I would install them especially if the building is tall, imagine snow falling 20' before hitting a child. They would also help you in a legal case because at least you did something to prevent injury. They do work too - I live in a snowy area and they do work, if the building is heated than they still allow the water to drain. I've called out the S-5 before and it seems fine.

 

[j19]

OHIOMatt makes a good point about making sure that the metal bldg supplier is ok with putting the snow guards on the roof. One other thing, I think most snow guard suppliers think of their guards as part of an "system", which would probably include several rows of guards spaced several feet apart up the slope. I don't think it is proper just to put a line of them over the doors. Check with the supplier though.

 

[Forensic74]

I think you need to spend some nominal money upfront to have the EOR of the building look at this. My concern would be if you started a drifting condition up there due to piled snow at the guard. PEMB's have little spare capacity and I've seen time and time again how they skimp on design. Are you sure an engineer even took a good look at the original design? This is why I see so many PEMB failures. A lot of clients dont realize the value of robustness until half of their building is on the ground because the purlins buckled and pulled the main frames down.

 

[SrVaro]

The first question that needs to be asked is are the doors going to be open or closed most of the time. If open, the snow gaurds may cause ice build up. And this will weight much more than the snow. The heat from the "center" of the building will melt the snow on the metal roof. It will slide and be stopped by the snow gaurd. If the door is open, the temperature will be lower on the roof above the door and re-freeze. You should to review with the PEMB design firm. I know that the building was not designed for this load case, but with this roof slope there is a chance it might be able to handle this special unbalanced load case.

There would also be a concern of just putting at the door causing a non-uniform load on the purlins. They may have been designed with load on-off-on adjacent bays, but not partially within some bays. And the edge purlins would be a concern for the possible additional load as described above.