Ice Dams Beware

By Megan Kramer, Performance Homes Consultant

ice dam pic.jpg

When I started in the energy efficiency field my first supervisor told me that I would never look at buildings the same again... Well, Dave, you were right. Driving around in the winter it is easy to examine roofs throughout the neighborhood and get a sense of what efficiency challenges the home is experiencing. 

Ice dams generally are areas where warm air from the home is coming into contact with the roof and causing the snow to thaw and then freeze again forming ice. This ice then creates a dam and more ice builds up behind it.

The question is - the warm air from the home coming into contact with the roof. We need to examine the insulation and air sealing details of the home. Some basic observations and one simple test with a very fancy name, zonal pressure diagnostics, can help.

What are the possible air leakage culprits in the home pictures above? Well it all comes down to different aspects of the knee wall attic.


This is one example of how a knee wall area can be insulated. This essentially puts the attic area outside of the conditioned space of the home. 

Thank you to Green Building Advisor for this image. They are an incredible resource for all building details. You can even download a file to include in your own CAD drawing! 



air leakage detail.png

Primary Suspects for Air Leakage

  • Can Lights: If not rated as Air Tight and for Insulation Contact these lights can act as holes in your ceiling and need to be replaced.

  • Kneewall Blocking: If not blocked properly, the insulation will allow for air leakage.

  • Kneewall Access: The door between conditioned and unconditioned space allows for massive air leakage

A simple blower test helped us figure this one out. The can lights did not leak at all while the attic access created a mild wind storm. Upon further inspection it was pretty obvious that this access was not sealed or insulated. Zonal Pressure Diagnostics revealed the conditioned space of this home was connected to the attic and needs to be separated.

kneewall insulation.JPG

As you can see, the access was insulated and sealed with basic pressure fit foam board and weatherstripping. A new ZPD was done and indicated there are no more connections between the conditioned and unconditioned space so the heat will stay where it is supposed to and the ice dam issue will be solved. 

Winter is here and I am excited to see the results when the snow flies!