Flat and low-slope commercial roofs face some of the toughest conditions in winter. Unlike steep residential roofs where snow tends to slide off, flat roofs hold snow and ice in place, increasing structural stress and the risk of leaks. Understanding how winter weather affects a flat commercial roof helps you make smart, proactive maintenance decisions.
Why Flat Commercial Roofs Struggle With Snow and Ice
Flat roofs are designed with only a slight pitch—often around ¼ inch per foot—to move water slowly toward drains and scuppers. That minimal slope means:
- Snow accumulates evenly instead of shedding
- Meltwater moves slowly and stays in contact with the membrane longer
- Any low spots or deflection become collection points for water (ponding)
When temperatures swing above and below freezing, snow partially melts, then refreezes, forming dense, heavy layers of ice and slush on top of the roof.
Snow Load and Structural Stress
The biggest winter threat to a flat commercial roof is weight. Light, powdery snow may only weigh a few pounds per cubic foot, but wet, compacted snow can reach 15–20 pounds per cubic foot, and solid ice can exceed 60 pounds per cubic foot. On a large roof, that adds up to several tons of extra load.
Too much weight can:
- Cause the roof deck or steel joists to sag or deflect
- Create new low spots that worsen ponding in future storms
- In extreme cases, contribute to partial or total roof failure
Because many commercial buildings are designed for a specific “snow load,” repeated heavy storms or rain falling on existing snow can push the structure beyond its intended capacity.
Ponding Water and Freeze–Thaw Damage
As snow and ice begin to melt, meltwater should move into drains, scuppers, or internal leaders. If drains are blocked by ice, debris, or collapsed strainers, water has nowhere to go and starts to pond.
Persistent ponding:
- Adds extra weight on localized areas
- Increases hydrostatic pressure on seams, flashings, and penetrations, making leaks more likely
- Accelerates membrane aging and can damage underlying insulation
Repeated freeze–thaw cycles cause trapped water to expand in tiny cracks and seams, gradually enlarging them and turning small vulnerabilities into active leaks.
Blocked Drains, Scuppers, and Gutters
On many flat commercial roofs, snow and ice slide or drift toward parapet walls and drainage points, where they can form thick ridges or blocks. When this happens:
- Roof drains and scuppers freeze over or clog with slush and debris
- Meltwater backs up onto the roof instead of leaving the building
- Overflow can find its way into walls or through mechanical penetrations
Keeping drains clear is one of the most critical winter tasks for any flat roof.
Actionable Steps for Building Owners
To reduce winter damage on flat commercial roofs:
- Schedule a pre- and mid-winter roof inspection to check for low spots, loose seams, and drainage issues before they’re buried in snow
- Keep drains, scuppers, and gutters clear of leaves, ice, and debris so meltwater can flow freely
- Use professional snow removal when loads become heavy; avoid DIY shoveling that can puncture membranes or create unsafe conditions
- Monitor interior signs—new ceiling stains, wet ceiling tiles, or unexplained drips—after storms, which may signal ponding-related leaks
Partner With Bridgewater Roofing
Flat commercial roofs demand specialized winter care. Bridgewater Roofing can inspect your commercial roof, evaluate snow and ice risks, clear critical drainage problems, and repair seams, flashings, and membranes before small issues become major disruptions.
If your building has experienced heavy snow, visible roof sagging, slow drainage, or interior leaks this winter, contact Bridgewater Roofing to schedule a commercial roof inspection and repair. Proactive attention now helps protect your structure, your tenants, and your bottom line.