Prevent Ice Dams from Forming on Your Roof
When temperatures plummet and snow
starts falling, many of us reach for the shovel
or snow blower. Smart homeowners,
though, remember to look up too — and
check their roofs for ice. Ice dams are accumulations
of ice on the edge of the roof —
and they mean Big Trouble for you and
your home, so be on the lookout.
What’s the big deal, you ask? Ice dams
result in water seepage, which can rot roofs,
destroy insulation, flood attics and ruin
gutters. Moisture damage can extend far
inside the home, damaging ceilings, paintwork
and belongings. The dampness encourages
mold, too, which can trigger nasty
You may have heard that gutters cause
ice dams by providing a place for water to
collect. Wrong! You may also have heard
that installing heating cables along the gutter
line is the best way to prevent ice dams.
Wrong again! Yep, there’s a lot of misinformation
out there. Let’s look at where ice
dams really come from.
How Ice Dams are Born
In poorly insulated homes, warm air escapes
through the ceiling and into the attic.
If ventilation inside the attic is also inadequate,
all that warm air has nowhere to go.
Result: the roof’s temperature starts to
creep up higher than the outdoors air temperature,
causing accumulated snow on the
roof to begin melting.
Water then trickles down the slope of the
roof until it once again hits a cold patch,
usually the gutter. There it refreezes, gradually
forming a dam that prevents runoff.
Additional melting snow, having nowhere
to go, starts seeping inside the house — and
that’s where the homeowner’s headaches
A Cool Solution: Insulation and
The only way to permanently eradicate
ice dams is not to warm your roof up (with
heating cables) but to cool it down with
better insulation and attic ventilation. Until
then, you’ll go right on experiencing ice
dams in severe weather. Any other strategy
will provide a temporary fix, at best.
In northern states, attic insulation
should be at least 12 inches deep. Make
sure it is installed correctly, without any
gaps between sections, and in conjunction
with a vapor barrier. While you’re at it,
check that attic heating ducts are located as
far as possible from the roof.
Also check around light fixtures, chimneys,
bathroom fans and anywhere else
heat might escape upwards. If you discover
small holes, seal them up with caulk, spray
foam or weather-stripping.
Next, evaluate your attic’s ventilation
system. Are there adequate inlet and outlet
vents? If not, look into installing a continuous
soffit and ridge ventilation system.
Here’s how it works: a vent is installed that
runs the entire length of the roof at its apex.
We all know hot air rises, right? In this
case, the hot air now has somewhere to go,
naturally flowing up and out through this
new attic vent.
Meanwhile, that draught of air upwards
and outwards creates a vacuum, sucking
cold outdoors air into the attic via soffit
vents, further cooling down your trouble
zone. The beauty part is there are no fans or
wires or anything else to be maintained.
Nature does all the work for you!
Help! There’s An Ice Dam on My
Roof. Now What?
Your best strategy is to sit tight and wait
for the ice to melt away. Later you should
focus on preventing future dams by making
the improvements described above.
Before you decide to manually chip away
at an ice dam, know that it’s not recommended,
and best left to a professional. For
one thing, you could seriously injure your-
self. (Never, ever climb up on an icy roof. If
you must inspect the ice dam up close, use
a ladder and beware of falling debris.) Second,
forcibly dislodging chunks of ice could
easily damage your roof and gutters, worsening
your leakage problem.
If you really, really can’t stand just waiting
it out, here’s an ice-melting tip courtesy of
This Old House: Cut the legs off a pair of
pantyhose, fill with calcium chloride ice
melt and lie them down the slope of the
roof so that each leg crosses a section of ice
and the toes dangle over the edge of the
gutter. This should melt small channels in
the ice, allowing runoff to occur.