What is the minimum required distance for ice dam protection horizontally from inside the exterior wall for roofs with a slope of 4:12 or greater?

For roofs with a slope of 4:12 or greater, the minimum required distance for ice dam protection, measured horizontally from the inside of the exterior wall, is indeed 24 inches. This requirement is put in place to prevent water from backing up under the shingles and causing leaks and damage in the event of ice dams forming during freezing conditions. Ice dams typically occur when heat from the building melts snow on the roof, causing water to flow down to the colder edges, where it freezes again.

By providing a minimum of 24 inches of properly insulated and sealed space from the interior wall, roofing systems mitigate the risk of ice dams forming too close to the edge of the roof. This distance ensures that there is sufficient protection against the potential build-up of ice and allows melted water to safely drain off the roof without infiltrating the building structure. This distance is part of the building codes and standards intended to ensure long-term durability and performance of roofing systems in climates where ice dam formation is a concern.