I look for ice dams during a home inspection.
Ice dams can form on sloped-roof overhangs in cold climates that are subject to prolonged periods of freezing weather, especially those climates with a daily average January temperature of 30° F or less. Heat loss through the roof and heat from the sun (even in freezing temperatures) can cause snow on a roof to melt. As water runs down the sloped roof onto the overhang, it freezes and forms an ice dam just above the gutter. The ice dam traps water from melting snow and forces it back under the roof shingles and into the building’s interior.
Inspectors should look at the edge of the roof overhang for evidence of ice dams and look at the eaves and soffit for indications of deterioration and water damage. If the house has an attic, the underside of the roof deck at the exterior walls can be checked for signs of water intrusion.