What is the purpose of underlayment in roofing?

Choosing the purpose of underlayment in roofing as relating to protecting against ice and water infiltration is insightful, as this is a significant aspect of its function. Underlayment serves as an important secondary layer of defense against water that can penetrate the roofing system, particularly in vulnerable areas such as eaves, valleys, and areas prone to heavy precipitation. It acts as a barrier, helping to prevent moisture from infiltrating the roof deck or underlying structures, which can lead to wood rot and mold growth.

While underlayment may provide some benefits in terms of smooth surfaces for shingle application or enhance insulation slightly, its primary role is essentially to manage moisture, especially in environments where ice dams or leaks are likely to occur. This makes it a crucial component in maintaining the integrity of the roofing system over time and protecting the building from potential water damage.