How to Prevent Ice Dams and the Roof Leaks They Cause

Here we are in the midst of another cold Massachusetts winter and like every winter here in New England many property owners will have major issues with ice dams causing roof leaks and shingle damage.

Although it may seem as though ice dams are an unstoppable force of nature, they are actually quite preventable. Attics and cathedral or vaulted ceiling areas that have been correctly incorporated into the overall building envelope 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 stopped cold (pun intended).

Here a typical scenario for the formation of ice dams:

A house has a build up of snow on the roof.
The temperature outside is below freezing.
The temperature inside the attic is above freezing, thus raising the temperature of the roof itself to above freezing.
Because of the warm roof, the snow on top of it begins to melt from the bottom up.
This melted snow water tries to run down and off the roof.
As soon as the water reaches the edge of the roof it gets exposed to the freezing air.
The water refreezes as ice instead of snow in the gutters, if present, and along the edges of the roof.
As more and more melted snow water continues to run down the roof it just keeps freezing behind and on top of the previously frozen run off, forming a bigger and bigger ice dam.
So How Do Ice Dams Cause Roof Leaks?
The melted snow water doesn’t immediately freeze anymore after the ice dam has begun to take shape. Once the ice dam has built up a bit it literally 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 this roof, behind the ice dam, are basically 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 a pond or river on top of them.

So What Can You Do To Prevent Ice Dams?

First and foremost you must recognize that proper insulation and ventilation is the key(see image on right). If we are talk about an attic area then typically this means that the insulation needs to run up the walls of your house then over the attic floor joists forming an ideal insulation envelope. In the attic scenario only the floor of the attic should be insulated, not the underside of the roof!

Proper ventilation is also required. Outside air needs to be able to enter the attic so that the attic temperature is the same as the temperature outside. You achieve this ventilation through the use of gable vents, soffit vents and a roof 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 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 ore 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 more expensive than an 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. Kind of makes it even worse when you think of it that way doesn’t it?

What Can You Do About Existing Ice Dams?

If it’s the middle of the winter and you have ice dams or through past experience you think they will be forming soon 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 pro. What you can do is go to your local hardware store and buy a snow rake that has an extendable handle designed to pull snow off of the first few feet of the roof and attempt to pull some of that snow off, from the ground, before it has a chance to melt and refreeze along the roof edges. You can also do this once the ice dam has formed and keep it from getting any bigger and give it a chance to melt, hopefully.

Also, many roofing contractors, us included, work through the winter and often provide roof snow removal services in addition to their typical roofing services. This is a service we are happy to provide for our customers here in Massachusetts, for example. 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 also 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 (see picture on right). These actually work pretty good, however, they aren’t solving the real problem which, of course, is ventilation and insulation issues. They may be right for some homes in some circumstances though.

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 then 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 as a roofing contractor is potential damage to the shingles from the chemicals these tablets are made of (salt is no 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 for a greater problem.

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, these days, an extra layer of protection called ice and water membrane should be installed from the edge to at least 3 feet up the roof.