Metal roof with no snow guards, Poughkeepsie, NY (C) Daniel FriedmanSnow Guard Failures & Damage

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This article describes failures in snow retention systems for building roofs. We describe several types of failures that occur including damage to the snow fence or snow brake itself, damage to the roof covering, building leaks, loss of clamp-on, glue-on or other snow guard components and of course crashes of snow and ice onto shrubs, vehicles, and potentially people who have the misfortune to be beneath the roof eaves during a sudden release of snow and ice.

This article series illustrates types of snow guards or snow brakes or other snow retention devices used on metal, rubber, asphalt, and slate roofs and we explain and illustrate in photographs just how and where these devices are attached to building roofs. We give the reasons for snow & ice retainer use and their history.

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Snow Fence & Snow Guard Damage & Failures

Snow and ice sliding off of a building are dangerous conditions. that can injure people and damage property. What is less obvious until inspecting the roof of a building that has suffered heavy snow movement and slide-downs, is that there may be damage to on-roof components as well.

Snow edging off of a metal roof (C) Daniel Friedman Snow curling off of a lower metal roof (C) Daniel Friedman

The new metal roof on which snow was sitting had not been fitted with snow guards. Below we will look at more damage to this building from sliding snow. In earlier years we saw thin layers of snow projecting out of the roof edge (above left) and head an occasional soft WHUMPFF as that snow fell onto the lower roof (above right).

We thought that snow and ice might slide and fall off of this roof falling harmlessly to a lower standing seam metal roof and from there it might fall harmlessly to the ground in an area free of vulnerable shrubs and not along a walkway or path. Below is some of the snow accumulation on the same two roofs in 2014, before there was any trouble with sliding falling snow and ice. The calm before the crash.

Snow on upper roof before snow slide troubles (C) Daniel Friedman Thick snow on metal roof, not yet sliding off (C) Daniel Friedman

The thick soft snow blankets covering the upper and lower metal roofs shown above is deceiving. Changes in weather, rain, melt, freeze cycles can convert this snow covering into a very heavy, thick snow mass. Not every roof is accessible or even safe to try "raking" the snow off. Assuring an adequate structure of the roof combined with snow brakes or guards may be in order in these situations.

Below at left is a photograph of thick frozen snow curling over the end of the lower metal roof and at below right is a modest amount of roof snow fallen harmlessly to the ground to the left side of a covered walkway.

Snow & ice ready to fall from a high roof (C) Daniel Friedman Roof snow falls to ground in a harmless area (C) Daniel Friedman

These relatively trouble-free conditions recurred for the first few years of the building's life - but, then, there had not been heavy snowfall, rain, freezing, and thick roof snow and ice loading.

The winter weather of 2014-2015 dumped heavy snow in areas of the Northeastern U.S. the same lower roof as shown above, sported a nice thick blanket of snow and ice (below). Given prior years' experience we weren't too worried about snow sliding off of this lower roof nor the larger upper roof above it. That was a mistake. We should have been a little worried. At below right you can see the situation: a large low-slope metal roof on an upper floor accumulates snow that's going to fall onto the lower one.

Notice my arrows pointing to that nice vertical plumbing vent on the upper roof? And the gutter on the upper roof? Hmmm.

Snow projecting past the roof edge ready to fall (C) Daniel Friedman Snow on roofs waiting to make trouble (C) Daniel Friedman

We heard a horrible tremendous CRASH and the building shook. A huge section of snow and ice had fallen from the upper roof onto the lower one. Happily the lower roof structure withstood the impact without damage, and happily too the standing seams on the lower roof were not flattened by falling ice. They could have been. It was time to start thinking about snow guars. CRASH! again. And again. I went out for coffee.

Snow slide off of high metal roof (C) Daniel Friedman Snow on ground after falling off of metal roof (C) Daniel Friedman

We visited this site again at night to notice the height of the bank of snow that had slammed down onto the lower shed roof and thence onto the ground (photo above right). Snow that had fallen from the two roofs was now piled from ground level to nearly the height of the roof eaves.

Gutter being bent by snow and ice creeping off of roof eaves (C) Daniel Friedman The structure withstood the crashing. And nothing vulnerable was in the path of the falling snow and ice at this building.

We observed (left) a thick heavy blanket of snow and ice easing slowly out past the roof edge. One might wonder just how much of that load is being taken onto the gutters affixed to the fascia board.

The condition of the two roofs and on-roof components like plumbing vents & gutters remained an open question.

The next inspection that was made of this roof was months later after snow had melted and the roof surface was dry.

Plumbing vent damage risks roof leaks and means Add Those Snow Guards

This was the first on-roof observation we made once snow and ice were clear of the roof: a bent over pluming vent. Who would have thought it? Sliding snow from the upper roof bent over this large ABS plumbing bent and broke it right off inside the roof cavity.

Notice that yellowish color at the broken end of the vent? That's foam insulation. This roof is installed over a cathedral ceiling with foamed insulation. That's not a design that tolerates water in the roof structure very well. Looks like a leak point.

The second photo (below right) shows the broken off ABS stub inside the roof cavity. The foam insulation was found to be a bit wet around the vent and was left to dry. Had this defect gone long un-noticed rainwater leaking into the roof structure would have eventually risked a costly mold catastrophe.

Pumbing vent damaged by sliding snow (C) Daniel Friedman Roof damage at plumbing vent means needed snow guards (C) Daniel Friedman

We jury-rigged a temporary plumbing vent out of soda bottles, mouth down, to direct any rainfall into the vent interior (below left), giving time to cut and prep and repair the broken plumbing vent. I'm not claiming this is an IAPMO-approved design, it's a stopgap measure to keep water out of the structure. For details about how we repaired this mess see PLUMBING VENT REPAIR .

Plumbing vent made out of soda bottles (C) Daniel Friedman

Gutter Damage from Roof Snow & Ice Means Add Those Snow Guards

Roof gutter loaded with snow and ice (C) Daniel FriedmanLots of folks have seen gutters on the ground or hanging by one nail from homes in snow country, and in some locales people just give up on gutters entirely, relying on other methods to get roof runoff away from the building.

Here we illustrate a more subtle gutter failure: the roof gutter was well secured to the building, covered with a screen, and built to withstand a bit of snow curling over and falling off of the roof edge.

Or so the designers thought. And indeed on some roof areas this strategy works just fine (at left).

But if we skip the obvious cases of gutters ripped clean off of the building by snow and ice slides, what about gutter snafu's that are not so visible from ground level?

Our photo at below left illustrates a couple of points:

First, gutter screens slow the gutter clog rate they do not prevent gutter clogging - ever. The gutter screen design should include easy removal for cleaning.

While the gutter screen had kept leaves out of the gutter, the crud in this gutter consisting of dirt washing down from the roof and small organic debris particles was the accumulation of about four years.

Just sending this fine dirt on into the downspout is ok on a system that drains to daylight and easy to clean, but for long buried downspout drain systems it's important to keep crud out of both the gutter and the downspout drain system.

Details about this gutter and its screen are at GUTTER SCREENS but I wouldn't' go there right now. Let's stick to ice and snow damage.

Second, even modest snow an ice sliding off of a roof is likely to leave the gutter bent downwards, eventually popping most of its support brackets. This particular gutter was additionally secured to the fascia so it wouldn't fall off of the structure.

In a forensic detail worth noticing, the dirt in the gutter was accumulated at its forward edge (visible in the second photo at below right) meaning that the gutter had been somewhat bent by those earlier years of presumed-innocent snow and ice slides down the roof. As this is more than one season's worth of crud in the gutter I think this gutter had been bent down for some time before this investigation.

Gutter damage from sliding snow & ice (C) DanieL Friedman Bent gutter dirt details shows the history & duration of period of damage - a forensic detail worth noting (C) Daniel Friedman Gutter after repair of snow and ice damage (C) Daniel Friedman Eric Galow

Our third gutter photo above shows the gutter after it had been carefully straightened and its mounting clips re-used. We did not replace the perforated screen as the contractor (Eric Galow, Galow Homes) intended to add more gutter supports.

See SNOW & ICE DAMAGE to GUTTERS for details about gutter damage where snow guards may have been a better idea.

Damage to the snow fence from snow loading

Bent failing snow fence on a metal roof (C) Daniel FriedmanOur photo at left shows that even if the snow fence or snow guard stays in place it may be damaged by large snow loads, particularly deep snow followed by rain or perhaps rain and freeze cycles.

This bent snow-fence on a high metal roof that itself holds a large area of snow (thus produces high snow loading on the snow fence) might have survived without damage if:


Improper Snow Guard & Fence Location

Snow guards too close to roof edge (C) Daniel Friedman Paul Galow showing long roof overhange (C) Daniel Friedman

The snow fence and glue-on snow guards on the building shown at above left are not properly located.

The lowest row of snow brake, fence, or snow guards on a roof should be placed over the building exterior wall. These snow guards are all located on the roof extension, overhang, or eaves. I didn't see any damage to the roof structure from snow-loading, but then this is a pretty small overhang. on larger roof overhangs the risk of snow load damage would be greater.

At a large roof overhang such as Paul Galow's roof shown at above right, snow guards located past the exterior wall might be asking for trouble.


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