This article in BUILDINGS – SMARTER FACILITY MANAGEMENT, by Janelle Penny ran in the January 2017 issue.
Plunging temperatures, slippery surfaces and extra precipitation combine to wreak havoc on roofs, from overloading drains to straining roofing materials through expansion and contraction. But a little planning can minimize the impact on your roof and ensure you’re prepared for the worst-case scenario. Protect your roof from winter’s worst with these tips.
Why Winter Can Wreck Roofs
The temperature changes and precipitation winter brings can cause a number of problems on your roof. Changing temperatures can be especially tough on single-ply membranes due to a phenomenon called supercooling, in which the membrane hovers around 5-10 degrees F. colder than the ambient air temperature, explains Tom Gernetzke, Project Manager for Facility Engineering, Inc., and a Past President and Fellow of RCI.
“Supercooling is particularly notable on clear moonlit nights where thermal radiation is emitted into space quickly,” Gernetzke says. “That subjects those membranes to much colder temperatures, and when it warms up in the daylight or part of it is next to a warmer building component, the forces of expansion and contraction can be even greater. The temperature differential on many roofing systems can be 130 degrees F. or more, especially if you go from a shadow line to an area that’s in the sun or an area that’s not covered by snow and ice to one that is. That can really strain some membranes.”
Adam Herring, Senior Project Manager at Highland Commercial Roofing, a provider of seamless cool roofs, recommends having a plumber check your drains while the weather is clear to ensure that rain, melting snow and ice can make it through, particularly if your building is in an area that receives considerable precipitation in winter. However, drain conditions can change quickly throughout the season, Gernetzke adds, so keep an eye on them to make sure you don’t end up with ponding water or excess weight on the roof. Drainage issues can surface under any of these conditions and can quickly become an emergency:
Frozen or clogged drains and scuppers: Roofing systems are intended to have good drainage at all times to get water off of the roof as fast as possible, Gernetzke says. Don’t let drains, gutters or scuppers stay frozen for long.
Trapped melt water: Water that becomes trapped under a layer of refreezing ice or snow can add thousands of pounds of extra weight, Gernetzke explains. “Most buildings that comply with building code are safe from having to worry about too much snow and ice stressing the building, but it certainly can happen,” Gernetzke adds. “A few years ago on the East Coast, there was significant structural collapse from the tremendous amounts of snow and ice the area received, which overstressed quite a few structures. A lot of the overload issues were the direct result of a large snow event of 12 to 36 inches of snow, followed by a warmup and then a rain event. What typically happens with those conditions is that the rain will melt some of the snow and compact it, but the drainage components are still frozen and don’t allow all of the water to drain off, so multiple events compound to create a bad situation.”
Ice damming: This occurs when snow builds up on the roof and then partially melts on a warmer day. If temperatures cool rapidly, the melted water that has migrated to the drainage areas freezes, forming a dam that holds back water and creating a ponding water area behind the ice dam, Herring explains. “Even with barriers installed at the edges of the roof, your roof system may not be able to handle the hydrostatic pressure from the water that dams up,” Gernetzke says.
Steep slope roofs are also at risk of ice and snow shear, where packed ice or snow slide down the sloped roof and shear off flashings, seams, joints, penetrations and even retention fencing.