What is Ice Damming?

Nov 29, 2011 by

In winters that are particularly snowy, thousands of people experience ice damming, and the destructive flooding as water rains down the inside of the exterior walls of their homes. Homeowners and insurance companies hate it, and dry-wallers, remodelers and painters love it.

We are your resource for preventing ice damming!

Ice DammingWhat is Ice Damming? Ice Damming occurs when heat from the house melts a layer of snow against the roof. The water flows beneath the snow to the edge of the roof where an overhang along the eave of the roof is colder and the water refreezes since the water at the edge of the roof is no longer heated by the house. When frozen, it creates a ridge of ice that builds up thicker and thicker. This ridge can be 8 inches thick! As new water from further snowmelt, thawing from rising outdoor temperatures, or rain comes down the roof, it gets backed up behind this “ice dam” or ridge of ice, and pools up. The water then finds it’s way back up under the shingles and leaks into the house– and can cause some pretty serious water damage.

Some Misconceptions

When we are re-roofing a home we can install a sticky membrane called Ice and Water Shield to the surface of the roof deck before we apply shingles. Then we’d essentially have two layers of roofing – one rubberized sheet, and one of shingles. If water pools beneath the shingles, we have the rubberized sheet as a back up. It mostly works, but it’s not a sure bet.

For most of us who aren’t re-roofing our homes at this time, our defense is to keep the roof cold, so we aren’t melting layers of snow and causing water to run down the roof and form the ice dam in the first place.

The roof deck should not be warm. We insulate our attic floors to prevent this, but when air is still leaking from the warm house into the attic, we realize we didn’t install enough insulation. Now the heated air leaks up into the attic (called convection as warm air rises) and since we don’t have enough insulation, the heat travels through the drywall or plaster celings into the attic (called conduction).

Further, many homes have ducts in the attic. Now we are really asking for more trouble. Ducts that carry the air from our heating system to rooms in our house are leaky and under-insulated. So we are essentially heating our attic. That’s bad news for keeping the roof cold and preventing ice damming, and bad news for trying to save energy. We’re paying for all that heat that we put into the attic “by accident” as all the heat is lost through attic vents.

Roof Deck CondensationThese vents were installed in attics to keep the roof deck cold in the winter, and vent out moisture. You see as heated air leaks into the attic it carries moisture (humidity) with it. Warm air holds a lot more moisture than cold air. In fact for every one degree we cool the air, we raise the relative humidity by 2.2% without adding any water. This is because cold air is “smaller air”, and gets full with less quantity of water than warm air does. So the vents are added to vent out this moisture so it does not cause condensation on the bottom of the roof deck and the mold and rot that comes with it. Of course, your first option is to stop the heat from escaping into your attic in the first place, and stop the humidity flow. After that, vents that wash the bottom of the roof deck with cold outside air, ensure that snow stays snow, and we don’t pay to melt it and cause ourselves a flood from ice damming in the process.

How to Remove and Prevent Future Ice Damming

So how can you truly prevent ice damming? Dr. Energy Saver performs these steps all the time; seal air leaks into the attic, seal ducts in the attic, insulate ducts in the attic, and add insulation to the attic floor. There are hybrid approaches and specialty items, but that’s the basic idea.

The Air Sealing and Insulation Relationship

Air sealing should ALWAYS be done before adding home insulation. A contractor who wants to hastily blow insulation in an attic without air sealing first, is taking the easy way out – for himself. Proper air sealing is much more difficult and takes much more time on average than blowing insulation. But with air sealing you don’t see so much of the work when you scan the attic, and with blown in insulation you see a lot; so it looks like something substantial was done. The insulator who blows insulation without air sealing first is committing malpractice and doing the customer a great disservice. Why? Now all those air leaks (can lights, drywall to stud seams, pipe and wire holes, openings around chimneys and duct chases, etc etc.) that need to be sealed are buried under a foot or more of insulation. They are very, very difficult to get to ever again.

But won’t insulation stop air leaks? No way. Insulation lets air flow right through it. It’s like having a winter coat on with just the stuffing, not the nylon shell.

Duct Sealing and Insulation

Blown in Attic InsulationDucts take particular care and attention. Your furnace may heat the air up to 100 degrees or more and send it through leaky sheet metal ducts through a 30 degree attic. It’s inevitable that heat gets into the attic it’s running through. Which means you get less heat delivered to the room intended – so you have to run the furnace more to keep your home heated – and that cost you money. Ducts must be sealed to prevent leaks in an attic and insulated well to prevent heat loss (and heat gain in the summer).

Attic vents, while less necessary in an attic that is properly air sealed, insulated and has it’s ducts taken care of properly, will keep the roof deck very close to the outdoor temperature, since they don’t have all the heat (and mositure) to vent out as they did before the home was “fixed”.

The Many Benefits of Ice Damming Prevention

Even in a perfectly treated house, ice damming is possible. How? Solar radiation. Most people can understand that the sun’s rays can go through the snow and heat up the roof and melt snow from underneath – even in an unheated building. But by having your attic properly air sealed and insulated as described, the incidences will be a lot less often (probably never), a lot less severe, and you’ll have a more comfortable house and save money on your heating fuel forever and ever.

It’s a repair that pays for itself. That is to say, if you don’t do it, over a number of years you’ll pay the money anyway in bits and pieces to your fuel company – and have your uncomfortable house to live in. It makes it a repair that feels good all around!

Dr. Energy Saver will assess your home and identify the major problems surrounding the cause of ice damming. Our proven methods will reduce ice damming from plaguing your home. Contact us today for more information about our services including air sealing, attic insulation, duct sealing, duct insulation, and more!

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