Houseworks: How to stop roof avalanches 

Ice guards eliminate the dangers of snow and ice from sliding off metal roofs in winter.   Photo by Al Klassen 

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If you have a metal roof on your house, then there’s a danger you need to understand. Metal roofs are almost always smooth, and warmth from the sun often starts winter trouble. Snow sitting on the roof can melt as the metal warms, then suddenly everything slides off the roof as one enormous mass. On roofs that aren’t especially well insulated, things are even worse. Heat escaping from the building contributes to melting, turning some of the rooftop snow into ice, with water underneath that lubricates the ice slab, making the situation even more treacherous. 

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I’m working on a building now where sliding ice has been an ongoing problem. It ripped the heaviest-gauge eavestrough that I’ve ever seen clean off the building, and even damaged the 2×6 railing of a wheelchair ramp running along one side of the place. Every winter that same ramp gets buried under two, three and sometimes even four feet of ice and snow dumped from the roof. Besides the damage, there’s the obvious safety and accessibility problem. 

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So I’m installing what’s variously called snow guards, ice guards or snow-retention rails. These fasten to the roof and mechanically prevent snow and ice from sliding freely off the eaves. Instead of an entire roof load suddenly becoming an avalanche, the snow and ice is held in place so it melts gradually in spring, with water running off the roof under the ice guard. 

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This kind of protection matters most above doors, walkways, parking areas and anywhere people routinely pass, but my recommendation is to protect the full length of the eaves. You never really know where someone might happen to be standing when a roof load decides to let go. 

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There’s an important structural issue to understand, too. Snow guards transfer the force of potentially sliding snow and ice back into the roof and its supporting structure. This is why strength and anchoring are key. You simply can’t attach a snow guard casually to thin roofing metal and expect it to last. Whatever system you use needs to be fastened securely and matched to the roof underneath it. 

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Many snow-retention systems are continuous profiles of bent sheet metal installed perhaps a foot or 18 inches above the eaves. That’s the most common type I see. Others use pipe-like rails. The system I’m installing now is the sheet-metal type, with 10-foot pieces bent into a triangular cross-section at the factory. In this particular design, the steel is actually folded over itself so the working section is two layers thick. 

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Ice guards need to be strong and anchored solidly to resist the downward pressures of ice and snow. This guard is made of a double thickness of metal and is fastened with over-sized roof screws. Photo by Al Klassen 

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On a typical wood-framed roof, long roofing screws can pass through the snow guard and roofing and bite deeply into solid wood below. Three-inch roofing screws are perfect for this. The building I’m dealing with now is different because its framework is entirely steel, so no wood to screw into. That’s why we’re using large-diameter #14 roofing screws driven into the extra-thick roofing metal on this particular building.  As with any snow-retention installation, the fastening method needs to suit the particular roof and the loads involved. In fact, the fastening method is at least as important as the guard itself.