May 9, 2016
Winter is Coming: Ice Damming 101
by John Argento, Barry Roofing
After a cool summer, many people have expressed concern that this coming winter will be severe. Homeowners should be aware of some surprising facts about ice dams and the leaks they cause.
An ice dam is a thick ridge of solid ice that builds up along the eaves of a roof. Dams can tear off gutters, loosen shingles and cause water to back up and pour into your house. Products such as Ice & Water Shield and other similar treatments prevent most ice-related winter leaks; however, leaks can still occur on perfect roof installations. This happened on tens of thousands of properly installed Chicagoland roofs during the unusually severe winter of 2013/2014. There were more ice damming leaks last winter than any winter in recent memory. This resulted from a combination of several large snowfalls with no warm days in between. Water trapped by ice was able to get higher than and beyond waterproofing materials.
Shingle-style roof systems are waterproof when water is flowing, but are not sealed systems like flat roofs. If water becomes trapped on shingle roofs, it can enter the building by flowing right under shingles and over metal flashings. Grace Ice and Water Shield and other rubberized underlayments can usually stop trapped water until the ice melts and the water can escape. However, these products are generally only installed in the critical areas where ice dam leaks typically occur. When water is trapped in non-treated areas, or higher than flashings, leaks can occur relatively quickly. This happens more frequently than most people are aware, but to a small enough degree that there is no stain on the ceiling underneath.
Ice dams occur when melting snow refreezes before it drains from the roof. This occurs near the gutters because overhang eaves exist beyond the heated space of the building. That is why the International Residential Code requires rubberized underlayment to be installed 24 inches past the interior heated wall on the roof. Dams of ice form over hours and days as the continuously refreezing water accumulates at the colder perimeter. Until a warmer period of days occur, icicles and ice dams get bigger and bigger. Ice normally melts from the bottom up and is often fed by more snow melt. This is how water becomes trapped under the ice and why the ice is called a “dam.” On newer roofs, rubberized underlayment exists from the gutter to a place six feet up the roof. If an ice sheet is trapping water more than six feet up, the odds of a leak increase. When a sheet of ice goes from the gutter all the way to the roof peak, a leak can occur anywhere on the roof, but is less likely where the underlayment exists. Winter leaks are also common where a roof meets a wall. These occur in a similar fashion when the ice creeps up higher than a flashing (a strip of metal used to stop water from penetrating the junction of a roof with another surface) behind siding. Flashings are typically installed between 2 ½ and 4 inches high up behind the siding. If ice travels up the wall six inches from the roof, the melting water can frequently pool higher than the flashings and a leak will occur.
Note that larger gutters, gutter pitch and additional downspouts do not make a visible difference in the size of ice dams and icicles. Gutters are quite small compared to the volume of water contained in roof snow. One inch of snow on the roof contains enough water to fill the gutters and downspouts solidly with ice and make them non-functional.
Although ice dam leaks occur even on perfect roofs, measures can be taken to prevent chronic ice dam leaks. Ice damming membrane can be installed higher up the roof or higher behind siding. In rarer cases, roofers can remove shingles and install flat roofing materials on lower pitched roof sections that drain poorly. Some Associations install heat cables if they are legal in the municipality. Most community Associations would find these solutions cost-prohibitive if they were performed on all units. We advise such solutions on a case-by-case basis if the same location leaks year after year or in mild winters.
John Argento is president of Barry Roofing and can be reached at (708) 653-3802.
Categories: Building Maintenance 101, Recent
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