Ice Dams and How to Fix Them
Anatomy of an Ice Dam
photo source: Montana State University Extension
Ice dams and the problems they cause
Ice dams are ice blockages on your roof that “dam up” or limit your roof from shedding melting water causing leaks. The misconception is that ice dams are caused by bad shingles, but this is not the case. Ice dams are in fact caused by ventilation issues that are worsened with insulation issues. If you notice ice building up along the eaves of the home, ice dams are happening. Leaking caused by them depends on the severity. If no ice build up is seen but leaks are occurring, condensation could also be the culprit. Condensation in the Attic is an article I wrote.
Not having the ice dam underlayment protection along the eaves underneath shingles is strike one and can cause leaking into your home. Ice dam barrier is a Minnesota building code requirement and an essential reactive deterrent to leaks caused by ice dams. It’s an adhesive backed felt paper that self seals around nails. Ice dam barrier does not solve the problem. Better ventilation and insulation does.
The videos above are from the Lomanco. They focus on ventilation and how air should move in the attic when everything is done correctly. Lomanco is one of the premier ventilation experts and why I use their products.
Ventilation and insulation requirements are staples of Minnesota Building code. Underperforming in either of these two categories can be strike two and three. This is why it is so important to get a contractor that understands what is happening with your roof. Every home offers a different mystery especially when built before 1960.
Why ice dams occur
Ice dams will occur when warm air in your attic rises and makes contact with the underside of your roof deck essentially heating up your shingles. This occurs along eaves where insulation is very minimal.
If snow is sitting on the shingles it will melt. The melted water will freeze and thaw depending on the temperature and degree of heat loss.
As the water freezes and thaws it can work its way under your shingles causing a leak. With enough snow and ice, melting water has no where to go and it dams up. The roof’s job is shedding water; it cannot retain it like a swimming pool so a leak can occur.
When ventilation is wrong, ice dams will form and be accompanied by other issues
Many building inspectors have certain things they look for during the roofing process:
A clean roof deck - The days of roofing over top of the old shingles have gone by. Many manufacturers will not warranty their product if used as a second layer. Reroofing over old shingles does not allow applying ice barrier or new felt.
Use of underlayments- Ice and water barriers and roofing felt are the second layer of protection beyond the shingles . Ice and water barrier is one item that inspectors look for during installation because of its ability to minimize ice dam damage. The number of rows of protection is related to the location of the interior wall.
Ventilation - Inspectors really pay attention to this because they understand how important it is. Non-circulating air in the attic is a root problem for ice dams and poor insulation makes it severe.
What solves the ice dam problems?
A new roof DOES NOT solve the problem- Just because a new roof is installed, there is no guarantee the problem goes away. If the contractor did not address the problem and mimicked what was there before, nothing will change.
Ventilation- (Watch the videos) The comparison example I demonstrate on the job with attic spaces is this: Open the front door preferably when there is a bit of a breeze. What was noticed? Some air movement? Maybe a little. Keep the front door open and open a window in a nearby room. Now what happens? Can you feel the air movement? Maybe the front door slams. That’s cross ventilation! That’s what the attic space needs to minimize the stack effect with warm air. Every home is different and there is no magic formula. It requires examining the attic to come up with a plan.
Adequate insulation is key- Sometimes only so much attic ventilation can happen, especially in the problem homes described. The only option left is insulating better. In Minnesota, 15” of attic insulation is the standard or what code requires when building a new home. More resistance to heat rising is a great option. I see a lot of homes with less than 6” of insulation!
An unconditioned attic- The attic space in many Minnesota homes is usually unconditioned meaning not heated or cooled. The goal here is keeping the attic space similar to outside temperature. Cross ventilation can keep the space close to the outside temperature. Good insulation can keep the heat from escaping into the attic.
Heated wires along the eaves- These do stop the ice from forming but I consider these as a reactive solution versus trying to solve the root issue. Sometimes they are the only option that works, so they should not be overlooked.
Conclusion: Ice dams occur usually when ventilation and insulation are not ideal in the attic
Ice dams happen when extremes occur in the attic, like poor insulation and poor air circulation. The problem can be greatly reduced if one or both are addressed. Each home can present a problem that requires a professional opinion. Call us this spring, summer, or fall and we can address any concerns you may have for the upcoming winter.
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