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How Can You Prevent Ice Dams This Winter?

Avoid expensive indoor water damage this winter by taking steps to prevent ice dams. Every year, homeowner’s insurance companies handle thousands of claims due to water damage from ice dams. The first step to prevent ice dams is to understand how they form.

Why Dams Happen

Snow falls evenly on the roof of your home, but unfortunately, it may not melt that way. Variations in roof temperature can cause snow near the peak to melt faster, while snow down near the eaves remains frozen. The cause is attic heat.

Warmth infiltrating from living spaces below rises naturally and accumulates in the upper zone of the attic, warming the underside of that portion of the roof disproportionately. Meanwhile, lower areas of the attic remain near freezing and contribute no warmth to the roof, particularly the portion extending above the eaves. Snowmelt flowing down the roof reaches the frigid zone of unmelted snow and re-freezes, gradually forming a mound of ice that dams the flow of roof runoff.

What Happens When They Do

Roofing is designed to effectively shed moving water as it flows to the gutters, not to withstand standing water. As water obstructed by the ice dam accumulates, it seeps under shingles and through joints between roof sheathing, dribbling into the attic.

Water damage to the attic includes warped wooden structural components and saturated insulation that no longer resists heat. As leakage penetrates further, ceilings in living spaces are saturated and stained, and possessions may be ruined. Water from the attic may also seep into interior wall cavities, triggering hidden mold growth.

To prevent ice dams, the primary goal is to keep roof temperatures uniform, equalizing the rate of snowmelt across the entire span of the roof. Here’s how to help that happen:

Ventilate and Circulate

Keep sufficient fresh air flowing into the attic to exhaust accumulated heat. Most attics rely on passive ventilation. Vents at the attic ridge exhaust rising warm air, causing a chimney effect that draws cold air in through soffit vents down at the eaves. For adequate attic ventilation to prevent ice dams, the ridge and soffit vents should be of equivalent size, supplying a minimum of one square foot of vent for every 300 square feet of attic floor space.

Seal the Attic Stairs

The pull-down attic stairs or attic access hatch is a major source of air leakage into the attic. Warm household air passing through worn weatherstripping or a gap caused by weak retraction springs on pull-down stairs flows into the attic and warms the roof. Use foam-backed weatherstripping tape to seal around the frame of the door or hatch and replace worn springs if necessary to make a tight seal.

Check Exhaust Vents

Make sure dryer vents as well as spot exhaust fans in the kitchen and bathroom don’t exhaust into the attic and contribute to heat accumulation. All indoor air should exhaust to the exterior through approved ductwork.

Upgrade Attic Insulation  

Proper insulation in the floor of the attic prevents heat transfer from the living spaces by conduction and radiation. It’s easy to add pre-cut fiberglass batts or have a professional blow-in more cellulose loose-fill. In this climate zone, the Department Of Energy (DOE) recommends insulation levels of R-38 to R-49. This equates with 12 to 16 inches of fiberglass or 10 to 13 inches of cellulose.

Install Sealed Recessed Lights

Old can-style lights recessed into the ceiling may be leaking both room heat and bulb heat into the attic. New recessed lights that are rated "IC, " or insulated contact, are air-sealed to prevent leakage and are also safe to be covered by attic insulation.

Check Chimney Flashing

The gap between chimney bricks and wooden framing of the house should be closed using L-shaped metal flashing. The flashing should be held in place by a sealant specifically rated for fireproof applications, not common spray foam.  

Close Openings

Use fireproof caulking to fill openings around plumbing pipes or appliance vents where they pass from living spaces into the attic. When the attic is dark, look for shafts of light from below that indicate air leaks. Also inspect attic insulation for any areas darkened by dust passing through air leaks.

Seal Ducts

Furnace ductwork routed through attics may leak hot air, warming the roof as well as increasing heating costs. An HVAC professional can pressure test ducts, pinpoint leaks and suggest sealing options. Ductwork should also be insulated to prevent heat transfer into the attic. 

For more information on techniques to prevent ice dams in the Chicago area, contact

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