How to Prevent and Repair Water Damage from Ice Dams

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How to prevent ice damming and clean up if you have water damage from an ice dam.

Ice dams can be a very destructive situation for a home in areas of the country with heavy or frequent snowfall and moderate temperature swings. Ice dams do not often occur where daytime temperatures remain below freezing for long periods of time. Snow is allowed to melt or evaporate gradually and ice dams are not formed. Knowing what to do before and after severe winter weather can help lessen the damage from ice dams or prevent them from occurring in the first place.

Ice Dam Causes

The greatest cause of ice dam formation is heat loss through the roof sheathing. Where attics are insulated on the floor, insulation should not be pushed up close to the roof sheathing near the eaves to prevent air flow from the eave to the ridge or gable vents. Other causes are heat loss around exhaust vents, large gaps around piping, insufficiently insulated bays of the attic, for attic air handlers – leaking ducts or missing duct insulation.

Blocked eave vents are another contributing factor to ice dam formation as proper air circulation is vital to preventing ice dams.

Ice Dam Prevention

To best way to prevent an ice dam is to keep the roof cold. That way, the snow on the roof eventually dissipates without making large amounts of melt water. The underside of the roof deck should not exceed 30 F. The best way to maintain low temperatures is by ensuring that there is adequate insulation and sealing gaps that let warm air pass into the attic from the house. The attic must also be ventilated, so that cold air is introduced into it and heated air escapes rapidly.

Some homeowners and contractors are under the impression that heat passing through the attic helps prevent ice dams, when just the opposite is true. Although excess heat moving from the attic through the roof rapidly melts snow, once the melt water touches the cold eaves, it quickly freezes and forms an ice dam.

If you have a furnace in the attic, it may not be possible to prevent ice dams. Increased insulation, however, can help. In this case you may need to insulate the roof rafters to block the heat from the furnace from heating the roof sheathing. It is important to keep an air space between the roof deck and the insulation in order to prevent a condensation buildup that can delaminate the roof deck. Prior to insulating, install polystyrene rafter air channels, which are available at home centers. Install unfaced insulation batts or blankets over the furnace's heating ducts to help reduce the heat buildup in the attic.

For the attic access, build a cover for it out of rigid foam insulation. See my article describing this at:

If the gable and ridge vents do not generate sufficient air movement to dissipate the heat, you will need a motorized vent at one end of the attic to exhaust the heat, and an adequately sized vent on the opposite end of the attic to draw in cold air from the outside. Have an HVAC contractor install a relay connected to the furnace blower controller to turn on the powered attic fan at the same time.

Minimizing Damage

Homes with ice dams on the roof also often get parallel lines of moisture on the ceiling. The dark lines in the ceiling are called shadow lines. Although there may be insulation on the attic floor, the bottom of the ceiling joists or trusses are not covered. They are exposed to the low winter temperatures and act like a thermal bridge to the ceiling below. This creates a cold strip on the ceiling on which condensation forms. Over time, this moisture results in mildew growth, which shows up as shadow lines. First, clean off the mildew with a solution of 1 quart of vinegar and 3 quarts of warm water. Rinse the surface with clear water and then let dry.

If the surface has been stained from the mildew or is otherwise discolored, it will need to be painted with a stain-blocking primer before applying the finish coat of paint.

Heat Tape and Heat Cables

There is much debate on the use of heat tape and cables for preventing ice dams. Proponents of these devices say that they will melt channels in the snow and ice and allow the water to flow past the ice dam from the underside. Opponents of them state that homeowners must remember to turn them on before a snowfall and off after the roof is clear, they burn out quickly and must be replaced often, they may melt the ice where they are installed, but the ice dam can form above them, they must be installed so that they create channels into the gutters, they can cause the shingles to become brittle over time. Not to mention that they won’t work when the power goes out. They also require a GFCI outlet installed near the roof line to plug the heating appliances in.

For homebuyers, if you see that a home has heating cables installed along the eaves, you can be pretty sure that they have had an ice dam problem in the past.

Heat Cables on Eave and inside Gutter

Heating cables may be a useful temporary fix for roofs with limited or no access to the eaves.

A new product called ZMesh is a low voltage ice melting system that is installed under the shingles of a new roof or roof replacement. It can be nailed or stapled through and provides long-life melting capabilities.

ZMesh Heat Tracing System ( )

Water Damage

In extreme cases of ice damming there may be water entering the living spaces of the home. The weather conditions may not be ideal for a cleanup, but it is important that you act quickly to avoid further damage. The worst scenario you will have to deal with is replacing the damaged portion of the roof and ceiling. But otherwise, you can do the cleanup easily and quickly when the damage is minimal.

By the time you start cleaning up the water damage, you should have already dealt with the ice dam and stopped any leaking water. If water is still leaking, try to collect the dripping water by placing a pail directly under it. You should also wrap the surrounding furniture with plastic. Also, remove any furniture that is situated directly under the leak.

The first step of the cleanup is to deal with the damaged portion of the roof. Before you do anything, check the durability of the roof as it may collapse on you. If you are well-equipped and experienced to replace the roof, replace both exterior and interior roofing. Usually this will require you to replace a roof tile or shingle and the damaged portion of the attic ceiling. A coat of paint might be a good idea as well. On the other hand, you could contact a contractor if you think you are not capable of the task.

Porous materials which have been wet through should be thrown away as mold may grow inside the pores. Carpet and rugs on the other hand, should be removed, washed and completely dried.

While doing the cleanup, also keep in mind a few safety tips. Wear proper clothing: use a pair of gloves, goggles and respirator if needed. Keep your gloved hands away from your face or any other part of your body. Be careful in using disinfectants; wear a respirator and be careful not to mix bleach with other chemicals that contain ammonia. And when scrubbing floors, move carefully to avoid from slipping and keep your working area free from clutter. Lastly, clean the tools used in the cleanup and removing the ice dam. Keep them dry and stored in a dry place so mold won’t grow on them. In addition, keep them out of reach of children to avoid any accidents.

Avoiding and cleaning water damage caused by ice dams can be done quickly and in a systematic order. The above tips are designed to help you but if you think you are incapable of the task, contact a professional contractor right away; one that can deal with the ice dam and water damage cleanup. But before you contact one, make sure that you check credentials and services offered contact your insurance company for accreditation and compare prices if you are on a limited budget.

After the Ice Dam Forms

Mechanical removal of an ice dam could damage your roof. It would be best to remove snow drifts from the roof before it starts to melt and refreeze to form ice.

On low-sloped or flat roofs, some homeowners shovel off all the snow. On a roof with a greater pitch, removing three or four feet of snow above the roof line will slow down the growth of the dam. There is a special tool for removing snow called a roof rake. Roof rakes are useful if the show is light. They should not be used on ladders.

Grooves cut into the ice will help drain away the water. This may be necessary if heavy rains or quickly rising temperature are expected after the ice dam has formed. While some people may try to cut a groove into the ice dam with a hammer and chisel or a metal shovel, these can damage the roof shingles. A better way is to fill a pair of panty hose or large socks with calcium chloride or other safe snow melting material and lay it across the dam. Do not use rock salt as it will stain the roof and siding. There is a pre-made melting tube you can buy online called the Ice Dam Blaster:

Whichever method you use, the best way to prevent ice dams and the damage they cause is to become familiar with your roofing system and take the preventive measures before the snow starts falling.

1 comment

Jerry Walch
Posted on Oct 16, 2010