As we brace ourselves for stormy season Dalal Steel would like to share with you the necessary snow accumulation prevention measures and removal guidelines for your consideration.

Building design considerations determine how much loading a roof can withstand. How does that snow load translate into cm of snow? This does not translate easily as snow can vary wildly in density from being light and fluffy to wet and heavy. It is not possible to determine a single value for the allowable height of snow that a building can safely support. In addition, the underlying snow density increases due to melting from the building heat loss and as water is absorbed from the melting snow above. As weather and temperature changes continue, ice may build up under the snow layers, further increasing the building roof loading intensity. This ice build-up also causes additional water back-up on the roof deck. This ice build-up also causes additional water back-up on the roof deck.  It is important to know your roof’s design capacity and monitor your own building.

Roof pitch makes a notable difference in all aspects of snow buildup on a roof. A high slope roof (i.e., more than 3:10) can experience conditions where some or all of the snow slides off of the roof. By contrast, a low/mid slope roof (i.e., less than 3:10) will not typically see the same sort of snow sliding, meaning it is more likely to build up and accumulate over time, typically getting icier and denser as it does so. This is a concern across the surface of the general roofing area, but it is a particular concern anywhere there is a change in height or where a vertical surface is encountered, such as a parapet wall, equipment, etc. In these locations, windblown snowdrifts can become trapped, so instead of blowing off of the roof, they accumulate in these areas, creating concentrations of heavier than planned weight. The accumulated snow can also find its way above flashings, and its thawing and freezing can eventually cause water leaks into the building.

If a building already has a significant amount of snow or ice, and a new storm is expected in a few days, safely reduce the snow uniformly before the next storm. Additional rain and snow can significantly increase the roof loads. Below are some pointers for snow removal procedures.

·         Visually inspect the roof system to identify unusual deflections of frames, purlins, or joists. Starting in this area, remove approximately one-half of the snow depth in a pattern that does not cause an unbalanced loading condition on the frames or purlins.

·         Identify areas where immediate roof bracing/support is necessary. Or if the building has additional unaccounted for loads, suspended or from the exterior.

·         In general, the shoveling pattern should progress from each endwall of the building towards the center. On larger roof areas, additional people working from the center of the building to the ends is recommended.

·         Remove drifted areas first, down to a level with other snow. If an area has drifts 1m deep and the main roof is 0.5m deep, trim off the drifts to 0.5m before proceeding.

·         Remove snow from the eave towards the ridge, sliding the snow off the roof over the gutter.

·         Remove the snow from the middle one-third of each bay for the full width of the building, beginning with the most snow packed bay. Complete snow removal on the remainder of the building.

·         On gable buildings, remove snow on both sides of the ridge at the same time.

·         Remove the remaining excessive snow depth in the same manner as described above.

·         Never use metal shovels or “scrape” the roof down to the surface of the panel. Remember, the objective is to relieve the excess loading condition due to the weight of the snow, not to completely clear the roof panel of all snow and ice.

·         Attempting to scrape the roof will result in broken fasteners, creating roof leaks, damaged panels and/or damaged trim. Preferable to use a push broom

·         Keep gutters, downspouts and roof drains open and free flowing to prevent water back up and ice build-up on the roof system. Ice damming conditions are especially likely on the north side of a building and in shaded areas.

·         We emphasize the importance of removing it uniformly from the entire surface of the roof, starting in the areas of accumulated snowdrifts, and then moving evenly across the roof from there.

·         Do not attempt to remove ALL snow down to the roof covering (keep 8-10cm). This will help avoid damaging the roof membrane.

·         Piling snow from one place on the roof to another, even in small areas, is clearly counterproductive and can cause structural problems.

Keeping People Safe:

·         Begin snow removal BEFORE the condition becomes critical.

·         If possible, remove snow without getting up on the roof. Using draglines through the snow, working from the endwalls, can sometimes accomplish this.

·         Anyone going up onto a roof even in the best conditions needs to follow proper safety procedures, and this is certainly magnified when the roof is covered with snow and/or ice. Watch for any “fall through” hazards like skylights. These panels are not intended to support roof foot traffic loads.

·         Metal roof systems are extremely slippery when wet. It may be necessary to use ladders, manlifts at the end of the building to avoid sliding snow.

·         Safe access from inside or outside the building needs to be assured, along with the use of a safety harness or similar precautions.

·         Certain areas of the roof deserve obvious attention, such as the roof edges and near any snow-covered skylights or hatches.

·         All of this is easier to accomplish when the snow is fresh and likely more easily handled. This makes timing of the removal important to worker safety as well, since it can mean the difference between smooth removal and extra exertion.

·         Never send one person alone on a roof to remove snow.

 It is up to the individual property owner to consider the benefits and dangers of snow removal and decide their own course of action. Remember to consider the depth and relative moisture content of your snow and the capacity of your roof structure in making your decision to remove snow or not.