Snow load removal and safety guidance

After the collapse of the Palmer Library roof last month, and a fatal roof collapse that killed an Anchorage woman, the Matanuska-Susitna Borough is urging residents to follow FEMA guidelines when it comes to warning signs, risks, and safety of residential and commercial rooftops and the snow loads many are carrying.

Some warning signs of overstressed roofs in wood and steel structures showing noticeable signs of excessive ceiling or roof sagging before failure.

More common warning signs common in wood, metal, and steel constructed buildings include sagging ceiling tiles or boards, ceiling boards falling out of the ceiling grid, and/or sagging sprinkler lines and sprinkler heads.

Sprinkler heads may deflect below suspended ceilings; popping, cracking, and creaking noises; doors and/or windows might not be opened or closed; cracks in walls or masonry; severe roof leaks; and excessive accumulation of water in non-drainage locations on low sloping roofs.

FEMA warns that if any of these warning signs are observed, the building should be promptly evacuated and a local building authority and/ or qualified design professional should be contacted to perform a detailed structural inspection.

After a major snow event, such as the massive snowfall back in December, most residents concentrate on removing snow from their driveways, while the cities and the Borough work to clear the roads. FEMA adds that after a snow event, snow removal may be in order. It is recommended that people try to use resources such as a local building authority or a qualified design professional familiar with the snow conditions of the region. If the snow needs to be removed, it should be done by a qualified individual who will follow necessary protocols to reduce the chance of personal injury and lower the potential for damaging the roof covering during the snow removal process.

“I recommend using a contractor to clear snow from your roof if you need to have the work done,” says Ken Barkley, the Director of Emergency Services for the Matanuska Susitna Borough.

Snow accumulation in excess of building design conditions can result in structural failure and possible collapse. Structural failure due to roof snow loads may be linked to several possible causes, including but not limited to unbalanced snow load from drifting and sliding snow.

When snow accumulates at different depths in different locations on a roof, it results in high and concentrated snow loads that can potentially overload the roof structure.

As the temperatures start to warm up over the next few months, there is the chance for rain-on-snow load. Heavy rainfall on top of snow may cause snow to melt and become further saturated, significantly increasing the load on the roof structure.

And with the warm temperature, as Borough residents have seen take place, there is also snow melt between snow events. If the roof drainage system is blocked, improperly designed or maintained, ice dams can form, creating a concentrated load at the eaves and reducing the ability of sloped roofs to shed the accumulated snow. On flat or low sloping roof systems, snow melt may accumulate in low areas on roofs, which can result in a concentrated load.

Many Alaskan homes are constructed with simple roofs that have steep slopes, and these roofs shed snow most easily. Roofs with geometric irregularities and obstructions collect snow drifts in an unbalanced pattern. These roof geometries include flat roofs with parapets, stepped roofs, saw-tooth roofs, and roofs with obstructions such as equipment or chimneys.

There are some safety measures to take during snow removal that can help minimize risk of personal injury. First, and foremost, any roof snow removal should be conducted following proper OSHA protocol for work on rooftops. Always have someone below the roof to keep foot traffic away from locations where falling snow or ice could cause injuries. Along with that, make sure someone confirms that the area below the removal site is free of equipment that could be damaged by falling snow or ice.

Whenever snow is being removed from a roof, be careful of dislodged icicles. While pretty to look at, an icicle falling from a short height can still cause damage or injury. Keep a safe distance away from the eave to remain outside of the sliding range. And don’t forget about buried skylights under all that snow. They can pose a high risk to workers on a roof removing snow, so if possible, properly mark this hazard.

There are some recommended methods of snow removal that will allow a qualified individual to remove snow safely, while at the same time minimize risk of personal injury and property damage. Contrary to what people may think, completely removing snow from a roof surface can result in serious damage to the roof covering and possibly lead to leaks and additional damage. FEMA advises leaving at least a couple of inches of snow on the roof.

Do not use mechanical snow removal equipment. The risk of damaging the roof membrane or other rooftop items outweighs the advantage of speed. Also, don’t use sharp tools, such as picks, to remove snow. Use plastic rather than metal shovels. Once drifted snow has been removed, start remaining snow removal from the center portion of the roof.

Remove snow in the direction of primary structural members. This will prevent unbalanced snow loading. Do not stockpile snow on the roof. Also, keep snow away from building exits, fire escapes, drain downspouts, ventilation openings, and equipment.

It may seem like a good idea to use that metal snow rake, but metal snow rakes can cause damage to roofing material and pose an electrocution risk and should be avoided. It might be better to use a long-handled non-metallic snow rake from the ground, thereby reducing the risk.

Upon completion of snow removal, the roofing material should be inspected for any signs of damage. Additionally, a quick inspection of the structural system may be prudent after particularly large snow events.

Snow removal is a dangerous activity that should only be done by qualified individuals following safety protocols to minimize risks. FEMA advises that at any time there is concern that snow loads may cause a collapse of the roof structure, cease all removal activity and evacuate the building.

For more information, contact the FEMA Building Science Helpline at www.FEMA-Buildingsciencehelp@fema.dhs.gov or call 866-927-2104.