Winter is coming

The change of seasons is upon us, and many areas of the U.S. already have experienced significant snowfall. As a roofing professional, you may believe the initial concern after a heavy snowfall is damage caused by ice dams and/or water intrusion from vulnerable penetrations or flashings. However, snow accumulation has the potential for damage well beyond such relatively minor roof repair issues.

A cubic foot of snow can weigh as much as 30 pounds. Loads imposed on buildings by snow accumulation can reach critical limits that could cause a structure to partially or completely collapse. Heavy snow loads also may cause enough deflection in support members to damage electrical conduits, natural or propane gas lines, water or fluid piping, and other building appurtenances. Significant snow accumulations combined with freeze and thaw temperature cycles can affect roof system drainage and allow water intrusion to buildings.

To help contractors address these issues, NRCA developed a snow remediation hazard analysis that offers suggested controls for these hazards.

Steep-slope roofs

The primary concern for snow-covered steep-slope roofs (slopes greater than 4:12) is eliminating or preventing ice dams. Ice dams occur when snow on upper roof surfaces melts because of heat loss from the building, sunlight or warmer ambient temperatures and runs down the roof only to refreeze at cooler overhanging eave surfaces. It forms a dam that prevents water from draining from the roof. Water then can back up under roof shingles, tiles or other materials and enter the building. Snow load is not ordinarily a major concern for steep-slope structures.

However, other hazards for snow-covered steep-slope roofs include:

• Inability to note skylight locations
• Tripping hazards like vent stacks and cable lines
• Unstable ladder access or unavailable ladder tie-off points
• Fall protection, lack of anchor points and/or inability to anchor without roof damage
• Pedestrian traffic for multiunit, steep-slope structures during periods of snow removal
• Possibility of roof damage from metal shovels
• Homeowners or untrained personnel attempting to clear snow buildup
• Worker exposure to cold, snow and ice that may result in hypothermia, frostbite and slipping hazards

Ways to control these hazards include:

• Using extension snow rakes to remove snow from eaves 3-4 feet from the fascia (Plastic tools are less likely to damage roofing materials.)
• Obtaining interior access to determine skylight locations
• Flagging hazardous skylights, vents and lines before snow season to highlight their locations and/or taking roof photos to locate obstructions
• Using industrial or agricultural steamers to remove ice dams (workers remain on ladders)
• Making sure gutters are unobstructed to facilitate water runoff to prevent dams (De-icing cables and chemical melting products may help, but roof system manufacturer restrictions may prohibit their use.)
• Incorporating permanent, weather-resistant fall-protection anchors into structures susceptible to critical snow buildup and engineering them to allow easy lifeline connection under hazardous weather conditions
• Improvising temporary anchor points to provide worker protection if permanent anchors are not available or “first man up” hazards cannot be eliminated
• Installing temporary canopies over entrances and exits or closing some access points if snow-removal operations or potential snow slides present danger (Ground monitors who use control flagging can assist in directing pedestrian traffic away from snow-dumping areas and removal staging areas or toward designated building access points.)
• Using chicken ladders (crawling boards) as work platforms if they can be secured over the ridge
• Making sure workers are dressed properly in layers with warm coats, shirts and pants along with quality gloves and a hat; sun protection may be needed
• Training roofing workers in roof hazards, fall-protection equipment and setup, and snow remediation hazards and procedures

Low-slope roofs

Weight is the primary concern for snow-covered low-slope roofs (slopes of 4:12 or less). Structures should be designed to withstand expected environmental live loads so they are able to hold the weight of even extraordinary accumulations of snow.

Other hazards associated with snow-covered low-slope roof systems include:

• Inability to note skylight locations
• Tripping hazards such as vent stacks, conduits, drains and piping
• Inoperable roof hatches
• Too much stress on support members from snow remediation efforts; as snow is removed or relocated, locating structural supports is critical
• Unstable ladder access or unavailable ladder tie-off points
• Lack of anchor points or inability to anchor without roof damage
• Snow blockage of unit heaters or rooftop HVAC units
• Public access to low-slope structures or surrounding property during periods of snow removal
• Employee and public entry to structures critically loaded by snow buildup
• Possible roof system damage from metal shovels and equipment parts
• Untrained personnel attempting to clear snow
• Deflection of support members under snow load, which may break and damage electrical conduits, natural or propane gas lines, water- or fluid-carrying pipes, and other building appurtenances
• Worker exposure to cold, snow and ice may result in hypothermia, frostbite and slipping hazards

Ways to control these hazards include:

• Obtaining interior access to a structure to determine skylight locations
• Flagging hazardous skylights, drains, vents and lines before snow season to highlight their locations or taking roof photos to locate obstructions
• Clearing snow from roof hatches promptly from the roof side to allow safer worker access
• Cleaning gutters and drains to facilitate water runoff (Roof de-icing cables and chemical melting products may help, but roof system manufacturer restrictions may prohibit their use.)
• Installing temporary canopies over entrances and exits or closing some access points because of snow-removal operations
• Restricting building access until snow loads are reduced to a safer level
• Incorporating permanent, weather-resistant fall-protection anchors into structures susceptible to critical snow buildup and engineering them to allow easy lifeline connection under hazardous weather conditions
• Using warning lines and safety monitors in snow-removal situations where anchor points are unavailable and workers are suitably trained in fall protection
• Using plastic shovels, raising snowblower blades as high as possible to avoid membrane damage and installing track systems on snowblowers may put less stress on roof membranes
• Having an engineer or competent person determine snow loads and proper removal protocol so snow is removed without stressing support members (Snow remediation often involves only partial removal of snow, for example, by establishing “wind rows” where suitable rows of snow have been removed from the roof to relieve stress.)
• Using tarps or skid boxes with a crane or all-terrain forklift to aid snow removal by off-loading or blowing snow into them provided they are not in contact with the structure
• Having ground monitors who use control flagging assist in directing pedestrian traffic away from snow-dumping areas and removal staging areas or toward designated building access points
• Ensuring workers are dressed properly in layers with warm coats, shirts and pants along with quality gloves and a hat; sun protection may be needed
• Training roofing workers in roof hazards, fall-protection equipment and setup, and snow remediation hazards and procedures
• Planning for snow remediation with a thorough analysis of hazards, control methods, work procedures, assignments and structural review and discussing these items during a pre-snow season meeting of all involved

Plan ahead

Snow remediation from roofs is complicated from engineering and safety perspectives. Planning suitable approaches to snow accumulation as part of roof system maintenance contracts or less formalized customer service efforts demands analytics within your company and extra attention paid to your customers.

To access NRCA’s snow remediation document, go to nrca.net/snowremediation.

Harry Dietz is an NRCA director of enterprise risk management

For articles related to this topic, see:
“Ice dam busting”
“Snow damage remediation”