Short Answer
Yes. Water can back up beneath roofing materials and enter areas that are normally protected from runoff.
Detailed Explanation
Ice dams cause leaks by creating a pool of water behind the ice ridge at the eave. This water can back up under the shingles, under the underlayment, and even under the ice-and-water membrane if the dam is large enough. Once water gets under the roofing materials, it can reach the roof deck and enter the home — appearing as leaks at exterior walls, ceilings near exterior walls, or even in the attic. Ice dam leaks are particularly insidious because they can occur on roofs that are in good condition — the water is being forced backward under materials that are designed to shed water flowing downward. This is why ice-and-water membrane along the eaves is so important in cold climates — it provides a waterproof barrier that seals around fasteners and prevents ice-dam water from reaching the deck.
Why It Matters
Ice dam leaks can cause significant interior damage during winter. Proper ice-and-water protection and attic insulation/ventilation are the best prevention.