Which of the following is designed to provide effective protection against ice dams in low-slope roofs?

Two plies of underlayment are particularly effective in providing protection against ice dams on low-slope roofs due to their ability to create a watertight barrier that prevents water infiltration. In climates where snow accumulation occurs, the combination of heat from the building and cold temperatures causes ice to form and block drainage channels, eventually leading to ice dam formations.

By utilizing two layers of high-quality underlayment, you enhance the roof's resistance to water infiltration that can occur when melting snow runs down the roof and encounters the ice dam. The overlapping of the two layers helps in sealing any potential leaks, effectively preventing water from backing up under shingles and causing water damage to both the roofing system and the underlying structure.

Other options, such as wooden shingles, EPDM membranes, and foil barriers, do serve specific functions in roofing applications, but they do not offer the same level of targeted thermal protection against the specific problem of ice dams as the dual ply underlayment approach does. Wooden shingles are generally not ideal for low-slope applications, while EPDM membranes are more relevant for flat roofs, and foil barriers, although helpful in reflecting heat, do not provide sufficient waterproofing on their own to manage the ice dam issue effectively.