New homes in many areas require the use of either 90#felt or a self-adhering membrane installed on the edge of the roof to provide protection against ice dam leaking. While the cause of ice damming is indeed related to warm air escaping into the attic, ventilation of the attic plays a big part here. It is imperitive that you have either gable-end vents that are not obstructed, or a combination of soffitt vents and ridge vents. Many times, soffit vents will be obstructed by insulation, diminishing their effectiveness. The attic is designed to be as cold as the outside air, thus keeping snow from melting and causing ice dams. If you have a cathedral ceiling, the insulation cavity in the ceiling should include a baffle to keep air passageways open to allow the escape of heat and moisture. A home inspector will be able to supply aenough info to identify the causes and recommend a solution. And as stated previously, always choose an ASHI certified inspector. Good luck.