How to prevent roof collapse due to snow and ice
Adverse weather conditions can affect the structural integrity of homes and buildings and can lead to partial or complete roof collapse.
As slopes increase, snow loads decrease. The wind is partially responsible, as is the tendency for a sloped roof to shed snow by sliding. Sliding snow, however, can also increase snow loads if snow accumulates onto a lower roof or canopy.
Snow drifts accumulate on roofs in what is known as the “wind shadow” of chimneys, adjacent walls, or roof projections.
Additional loads produced by rain on snow can be significant, due to ice accumulation.
Buildings may be more susceptible to damage due to the following reasons:
- Poor drainage allows water to accumulate near the foundation. Foundations are affected by freeze/thaw cycles.
- Large icicles at the roof’s edge and ice dams in roof valleys can cause additional load and water damage when the melting runoff is backed up.
- Location of windbreaks can put the building within the “snow catch zone” and cause snow to accumulate on the roof.
- Overhanging tree branches.
- Additional equipment installed from rafters adds “dead load” to the roof.
- Insulation added to roofs prevents heat transfer that normally melts snow and reduces the snow load. Additional insulation allows snow to accumulate.
- Uneven drifting of snow.
Determining the structural integrity of a building is beyond the scope of this bulletin. However, a professional engineer should be consulted if one or more of the following warning signs appear:
- Broken or cracked rafters, trusses, studs, or columns.
- Twisted or deformed rafters or trusses.
- Building leaning or out of plumb.
- Loose fasteners.
- Cracked drywall or plaster on ceilings.
- Leaks from melting snow.
Removing snowRemoving snow from roofs is preventive maintenance and is a common-sense measure to reduce the risk of building failure. However, extreme caution is urged. Work from ground level and use a snow rake if at all possible. Many building contractors are also willing to remove snow from buildings they have constructed.
The information and recommendations contained in this material have been obtained from sources believed to be reliable. However, SECURA accepts no legal responsibility for the accuracy, sufficiency, or completeness of such information. Additional safety and health procedures may be required under particular circumstances.