What is an ice dam? Ice dams are a common cause of water leakage in your home’s attic and upper floors. But what is an ice dam and how are they caused? Is an ice dam a roofing problem or an insulation problem? An energy auditor can help you understand ice dams and how to prevent them from forming on your roof.
What Is An Ice Dam? – Your Boring Wiki-Style Definition
An ice dam is a ridge of ice that forms at the edge of a roof and prevents melting snow (water) from draining off the roof. The water that backs up behind the dam can leak into a home, damaging walls, ceilings, insulation, and other areas.
What Is An Ice Dam? – The Causes
This diagram shows a cross section of a home with an ice dam.
For ice dams to form there must be snow on the roof, and, at the same time, higher portions of the roof’s outside surface must be above 32°F while lower surfaces are below 32°F. Essentially, the air circulating in your home is circulating at different temperatures.
For a portion of the roof to be below 32°F, outside temperatures must also be below 32°F. When we say temperatures above or below 32°F, we are talking about average temperature over sustained periods of time.
The snow on a roof surface that is above 32°F will melt. As water flows down the roof it reaches the portion of the roof that is below 32°F and freezes. That’s when the ice dam forms.
The dam grows as it is fed by the melting snow above it, but it will limit itself to the portions of the roof that are on the average below 32°F. So, the water above backs up behind the ice dam and remains a liquid. This water finds cracks and openings in the exterior roof covering and flows into the attic space. From the attic it could flow into exterior walls or through the ceiling insulation and stain the ceiling finish.
What Is An Ice Dam? – The Solutions
How can you prevent ice dams? To stop ice dams, you need to stop the temperature of your roof deck from rising over the melting point of snow.
Vented roofs gained popularity in part because of their success in reducing ice dam issues.
Unfortunately, insulation alone CANNOT prevent ice dams, though varying degrees of insulation may seem to be the cause of ice dams. What you really want to do is: prevent the warm air circulating within your home from bypassing the insulation and attic air barrier and warming your roof.
So what is an ice dam? I mean besides a pain in the butt? Ice dams are a common problem in the northern section of the US and Canada. Understand first the roof warming up enough to melt the snow is the root cause of ice dams. Air leakage and to some extent insulation issues are where you should cast your eye if you’re having bad ice dams.