The primary reason for ice dams is heatloss into your attic. The main way that the that the heat gets into your attic is by air leakage. Unfortunately, many builders, and many building codes, don't address the issue.
I Agree that you should get an inspector, but be sure to get one that specializes in energy issues. You might check with your local utility company, as many have programs dealing with such things and are aware of who knows what they are doing.