ICE DAMS FORM when warm air, trapped in the attic, melts roof snow
from the under-side. Most of the melt occurs near the ridge, where temperatures are
highest. Water trickles under the snow to the eaves, where roof temperature is below
freezing, and forms an ice dam. |
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Ask homeowners why they insulate their attics, and most will
talk about comfort and energy savings. Ask a building professional the same question, and
you'll hear phrases such as "rot prevention" and "structural
integrity."
That fluffy pink blanket covering your ceiling does, indeed, do much more than keep
you warm on cold winter nights. It helps your attic stay cool and your roof stay cold.
That's the key to preventing ice dams maybe the most destructive home nemesis
you've never thought about.
"In colder climates, the most common weather-related claim we get is damage to
the interior of a house caused by ice dams," says Steve Marlin, assistant vice
president, USAA Property Policy and Catastrophe Operations.
An ice dam is exactly what the name implies: a barrier of frozen water that forms
where your home's eaves and gutters meet. Ice dams keep water from flowing freely off your
roof, forcing the water to pool and back up under shingles.
The consequences of this phenomenon can be severe. Water damage begins with the
sheathing to which shingles are nailed. This layer, which usually is plywood or
oriented-strand board, will begin to warp and eventually decay.
At some point, excess moisture will begin to build in the attic. This dampness will
be absorbed by insulation, making it much less effective. Ultimately, water may begin to
leak throughout the home's interior along rafters, across trusses, into walls and through
ceilings.
The causes
Many factors contribute to the buildup of ice dams. The main culprits are
poor insulation and poor ventilation. "When an attic is not well insulated and
ventilated, heat will escape from the house and warm the attic to the point where snow
resting on the roof will melt and run down," Marlin explains. "When it hits the
overhang of the roof and it's no longer being warmed by the interior, the water freezes.
Over time, it builds up and forms a small dam of ice."
The speed at which ice dams form and the severity of the damage they cause are
accelerated by clogged gutters, low roof pitches and even the color of the shingles darker
roofs absorb more heat and promote melting. Recessed light fixtures, especially older
models located in vaulted ceilings, also can create hot spots that contribute to the
problem.
Dealing with dams
Few people have the financial resources to commission a new lighter-tinted,
steeper-pitched, heavily insulated and well-ventilated roof. Even if they did, the most
architecturally correct roofs still can get ice dams if heavy snows are followed by sunny
days and bitterly
cold nights.
That being the case, homeowners should focus on two courses of action; First, do
whatever you can afford to lessen the possibility of ice dams. At the very least, clean
your gutters, add attic insulation and caulk any visible gaps in your ceiling. If you
believe ventilation is a problem, consider hiring someone to improve airflow. Your home is
a candidate for ventilation work if you peek into the attic and notice rusty nails or rust
spots on insulation, blackened sheathing, a musty smell or frost in the winter.
The second course of action is to install products specially designed to combat ice
dams. "One such product, a heating coil, is installed where the roof meets the
gutter," says Do Kim, director of engineering for the Institute for Business &
Home Safety (IBHS). "During the winter, homeowners can plug heating coils in and they
will prevent ice damming by melting that area [where roof meets gutter] and keeping the
roof warmer so it doesn't freeze. It works very well."
Heating cables do have some drawbacks, though. They're not terribly attractive, and
during hard freezes, they may need to be on for days or weeks at a time.
An alternative is to install a waterproof membrane along the edge of the roof under
the shingles. Made of polyethylene and rubberized asphalt, the material is self-sealing so
nail holes won't cause problems. "The product has been around for a long time, but
just recently builders have begun using it in residential construction," Kim says.
"Today, most of the northeastern and central states have adopted building codes
calling for use of this product."
A typical roll is about three feet wide, and a 75-foot roll can cost between $85
and $100. Building codes often require one row of the sticky-backed material, but for
extra protection, many professionals recommend two rows for a six-foot barrier against
backed-up water." |
