What is one of the purposes of roofing underlayment?

Roofing underlayment serves multiple important functions, one of which is to protect the roof sheathing before the roof covering is applied. During the installation of roofing materials, there can be instances where weather elements such as rain, snow, or ice may come into contact with the sheathing. The underlayment acts as an additional barrier, helping to prevent moisture from penetrating to the sheathing and potentially causing damage like rot or mold growth. This protective layer is crucial for the longevity and integrity of the roof system, ensuring that the sheathing remains dry until the primary roofing material (like shingles) is installed on top of it.

The other options do not accurately describe the role of roofing underlayment. It is not intended to act as the primary roof covering nor does it eliminate the need for shingles. Additionally, while it contributes to the overall roofing system, it does not provide structural support; that function is typically served by the roof framing and sheathing.