Ice Damming
Definition: Ice damming is a naturally occurring phenomenon that is a result of rooftop snow that has
thawed and refrozen into ice. This ice dam then impedes the flow of water as it runs down the roof.
Snow followed by rain after increases the likelihood of this phenomenon. It is also important to know that
ice damming is temporary and does no permanent damage to the roof system.
While homeowners may be nervous about the leak resulting from an ice-dam, they often get a lot of
comfort out of fully understanding the nature of ice damming and knowing that their home is still sound,
that the problem will end with the condition, and that their builder & trades are still competent and
knowledgeable in their fields.
Locations: While it is true that ice damming does occur at the eaves of the roof (over the unconditioned
portion of the roof and the gutters), there is a common wide spread misconception that ice-damming only
happens at this lower area of the roof as a result of freezing gutters or freezing at the overhangs.
Ice-damming can occur anywhere on the roof. It can happen as a result of: thawing & refreezing due to
external temperature fluctuation and uneven heat loss in different areas of the roof. Other areas include:
roof penetrations (plumbing vent pipes/box vents/attic fans/skylights), valleys, roof wall intersections, or
at pitch changes on the face of a roof that hinder the flow of water from above, packs on the roof face,
areas that are shaded at different parts of the day causing uneven melt, debris that blocks flow and
promotes buildup at the debris on the roof face or buildup in the gutter of ice & snow during the
precipitation fall or during the process of thawing & refreezing, gutters and roof overhangs not subject to
heat loss from warmer living spaces as is the roof above those areas, consistency of precipitation at time
of fall, quantity of precipitation (ex: may be light & fluffy, but so thick that takes a number of thaw &
refreeze cycles before it is off), snow/ice precipitation followed by rain (especially in areas like valleys
that receive high volumes of collective runoff and are also prone to ice/snow buildup).......etc. While this
is a comprehensive list, there may be some additional factors that have not been listed here.
What to do – Exterior: There is no fix for this condition other than to have the roof cleared of snow or
wait for it to clear naturally. Most contractors do not clear roofs due to the VERY HIGH risk of death or
injury to their roofing technicians by slipping and falling off of the roof. It is also recommended that
homeowners do not go on the roofs themselves for the same reason.
What we suggest is that homeowners let the roof clear naturally, since in general they must, because the
same conditions which are causing the ice damming make it unsafe to access the roof. Once the roof is
clear of ALL snow and packed ice, watch the areas that leaked through at least one heavy rain. If the
leak does not reappear, then it was very likely a onetime occurrence of ice damming. (Please note that
roof must be clear of ALL snow and packed ice – even after the fluffy stuff is gone, there is often still
packed ice on the roof.)
What to do – Interior: The main goal while experiencing an ice dam is to minimize the interior damage,
so that when it is all over, the least amount of repair work has to be done. The following are a few
suggestions. If a leak appears around a light fixture or attic fan, turn the power off to that fixture at the
breaker. Do not run bath fans that will carry additional hot moist air to the attic and roof – especially if the
vents are covered in snow and/or ice. One thing that can be done to help prevent drywall from buckling
or bulging is to poke a hole through the leak area and put a bucket under it, which allows the water to
drain rather than soaking into the drywall. It is the weight of saturated drywall that causes that buckling.
Once the roof has cleared and it is determined that the leak(s) was due to ice damming, allow the drywall
to dry completely, then spackle, sand, prime (MUST be well primed with a water stain primer BEFORE
topcoat), and finally top coat paint.
Conclusion: Hopefully this information will be helpful at present and in the future, whether you are a
tradesman, a builder, or a homeowner, both in diagnosing ice-damming and in educating others as they
encounter this condition. Feel free to pass this along to anyone that this might assist.
This picture is an example of an ice dam at an eave of a roof. Note the packed ice beneath the layer of
softer snow. The ice dam in this picture, while only visible at the edge, may extend up the roof slope a
few inches or multiple feet. This condition may develop anywhere on the roof and may or may not have
areas that are visible.