Ice Dams – Causes and Prevention

Here we are at the beginning of another cold Indianapolis winter and like every winter here in Indiana many property owners will experience issues with ice dams that will eventually cause shingle damage, roof leaks and the possibility of mold.

Although it may seem as though ice dams are an unstoppable force of nature, they can be prevented. Attics with cathedral or vaulted ceiling areas that have been correctly incorporated into the overall building envelope usually don’t have problems with ice dams and icicles in the cold seasons. Through the use of proper insulation and ventilation techniques, ice dams can be prevented.

Here an ice dam forms:

1. A house has a buildup of snow on the roof.
2. The temperature outside is below freezing.
3. The temperature inside the attic is above freezing, thus raising the temperature of the roof itself to above freezing.
4. Because of the warm roof, the snow on top of it begins to melt from the bottom up.
5. The melted snow water tries to run down and off the roof.
6. As soon as the water reaches the edge of the roof it gets exposed to the freezing air.
7. The water refreezes as ice instead of snow in the gutters and along the edges of the roof.
8. As more melted snow water continues to run down the roof it keeps freezing behind and on top of the previously frozen run off, forming a larger ice dam.

How Do Ice Dams Cause Roof Leaks?

The melted snow water doesn’t immediately freeze after the ice dam has begun to take shape. Once the ice dam has built up, it creates a dam that traps the rest of the water trying to run off the roof behind it. While this trapped water will eventually freeze, it may take a while and during that time a portion of the shingles on the roof, behind the ice dam, are submerged in water.

Now of course your roof shingles are obviously suppose to protect your home from the weather i.e. rain and snow. However, most roofing materials are not meant to have standing water on top of them.

What Can You Do To Prevent Ice Dams?

First and foremost proper insulation and ventilation is the key. In the attic only the floor of the attic should be insulated, never the underside of the roof. In northern climates such as Indiana, an R value of 48 is recommended. That is approximately 15-18 inches of blown insulation depending on what type of insulation you are using.

Proper ventilation is also required. Outside air needs to be able to enter the attic so that the attic temperature remains consistent with the temperature outside. You can achieve this ventilation through the use of gable vents or soffit vents in conjunction with cap vents or a ridge vent.

In roof systems with attic areas below them, it is fairly straight forward to have a contractor that knows what they are doing to correct any problems as far as proper insulation and ventilation. However, roof systems with a cathedral or vaulted ceiling below them that have these issues are much more of a project to correct, but they can be corrected.

In order to have a properly ventilated and insulated cathedral ceiling the contractor must install baffles within each rafter bay before installing the insulation. These baffles allow air to flow between the soffit vents and the ridge vent which keeps the underside of the roof the same temperature as outside. If these baffles are not installed in your cathedral ceiling then the contractor will need to remove the existing sheetrock and insulation from your ceiling in order to properly ventilate the area. This type of project will be a bit more expensive than a simple attic project.

In addition to the ice dam issue, if your attic is warmer than the outside temperature you are also wasting lots of money heating that space. So basically you are paying extra money on your heating bill for the privilege of growing nice big ice dams and icicles that cause roof leaks and destroy your roof.

What Can You Do About Existing Ice Dams?

If it’s the middle of the winter and you have ice dams there are some measures you can take. First of all, if you don’t have experience climbing on a roof in the winter, especially with snow on it, don’t do it! Call a professional. Many roofing contractors work through the winter and often provide roof snow removal services in addition to their typical roofing services. This is a service many are happy to provide during the winter as this is typically a roofers slowest time of year. Again, please don’t try and do this yourself. Between icy ladders and slippery roof surfaces, it is a recipe for disaster for the inexperienced.

There are some products on the market that can assist in preventing ice dams before they form and melting them if they have already formed. You should be able to find a home improvement store in your area that sells a product that is basically a coated, heated wire that you fasten along the edges of the roof and then plug in when the conditions are right for the ice dams to form. These actually work pretty well; however, they aren’t solving the real problem which, of course, is ventilation and insulation issues.

Most home improvement and hardware stores also sell pellets or tablets that are designed to be thrown up onto the roof from the ground. These tablets supposedly will melt the ice from the roof as they dissolve into the water that is running down the roof into the ice dam. I have no experience with these products so I can’t say for certain if they work as designed or not. However, some people say they have worked for their ice dam problems. A couple of things I would be worried about is potential damage to the shingles from the chemicals these tablets are made of (salt is not good for asphalt shingles), as well as possibly staining the roof with those same chemicals. And even in a base case situation this product is still just a band aid until the ventilation and insulation issues are addressed.

Proper Roofing Techniques For Cold Climates

In addition to making sure that the roof has proper ventilation and attic insulation there is an additional level of security against ice dam issues and roof leaks that all responsible and ethical roofing contractors should be taking in cold weather climates with regards to pitched, asphalt shingled roofs. When a new roof is installed, an extra layer of protection called an ice and water membrane should be installed from the edge to at least 3 feet up the roof.

This added layer of protection will help prevent leaks if ice dams do develop along the roof edges. The ice and water membrane will not prevent ice dams, it simply is added security to help protect the plywood or OSB sheathing beneath the asphalt shingles and prevent leaks should an ice dam form.

If you are not sure that you have the right amount of insulation and ventilation in your attic, you can call a licensed home inspector or roofing contractor in your area to come out and assess your situation. A little preventable maintenance now can save you big bucks down the road.