When snow on the roof becomes a problem: FEMA’s warning signs

What are the warning signs of too much snow on a roof?

FEMA's snow load safety guidance (FEMA P-957) lists the signs that a roof is overstressed. Wood and steel structures often show them before they fail:

• Sagging ceiling tiles or boards, or ceiling boards falling out of the grid
• Sagging sprinkler lines, or sprinkler heads dropping below a suspended ceiling
• Popping, cracking or creaking sounds
• Sagging roof members, including metal decking or plywood sheathing
• Bowing trusses
• Doors or windows that can no longer be opened or closed
• Cracked or split wood members, or cracks in walls or masonry
• Severe roof leaks
• Water collecting on a low-slope roof where it should drain

Why do roofs get overloaded?

Depth is only part of the story. FEMA points to four causes:

FEMA notes that simple roofs with steep slopes shed snow most easily. Weight also depends heavily on the kind of snow, and wet snow is far heavier than powder; see heavy wet snow vs light snow. Ice at the eaves is its own problem with its own fix, covered in what causes ice dams.

What about flat commercial roofs?

On the flat and low-slope roofs of stores, offices and warehouses, several of FEMA's warning signs show up inside the building: a sagging ceiling grid, sprinkler heads dropping below the tiles, water pooling where the roof should drain. Those roofs also have the shapes that collect drifts: parapets around the edge, step-downs between building sections, and rooftop units.

When removal is needed, FEMA's guidance for the qualified crew doing it includes:

1. Remove drifts first, at elevation changes, parapets and around equipment.
2. Then work from the center of the roof, in the direction of the main structural members, so the load stays balanced.
3. Leave a couple of inches of snow to protect the roof covering.
4. Use plastic shovels, not metal ones, no sharp tools and no mechanical equipment.
5. Do not stockpile snow on the roof, and keep what comes down away from exits, fire escapes, downspouts, vents and equipment.

FEMA also flags buried skylights as a high risk for anyone working on a roof. Owners should know where the skylights, drains and rooftop units are before the season, and keep the drains clear. Ground-level clearing for commercial sites is covered at commercial snow and ice management.

Should I clear snow off my own roof?

FEMA calls roof snow removal dangerous work for qualified people following safety protocols, and OSHA's guidance is to use methods that keep workers off roofs whenever possible. For a homeowner, that leaves one reasonable option:

• A long-handled, non-metal roof rake, used from the ground. FEMA notes it reduces the risk.
• Stand well back from the eave. Roof snow can slide at any moment, and even a short drop makes a falling icicle dangerous.
• Never use a metal rake. FEMA warns that metal snow rakes can damage roofing and pose an electrocution risk. Look up before you raise anything long; DTE Energy says to keep aluminum poles away from overhead lines.
• Do not climb up. If the roof needs more than a rake from the ground can reach, it needs a roofer with fall protection.

If you see the warning signs, do not try to fix it from below or above. Get out and call the building department.

Who handles roof snow in Macomb County?

For warning signs, call your city or township building department, or a structural engineer. For removal, call a roofing contractor equipped for snow work.

We clear driveways, walks and parking lots. Roofs are not part of a residential visit, so roof snow belongs with a roofer. On the ground, keep exits, vents and downspouts clear of whatever comes off the roof; our after-storm checklist explains why vents matter.