When is it necessary to use a roof underlayment?

A roof underlayment is an essential component in roofing systems as it provides an extra layer of protection against water infiltration, particularly in areas prone to ice dams or heavy rain. Underlayment acts as a secondary barrier should water seep through the shingles, ensuring that the underlying structure remains protected from moisture damage.

This additional protection is particularly critical in climates where ice dams are a concern, as these can form when melting snow refreezes at the eaves, creating a situation where water can back up under the shingles. Using a roof underlayment is a proactive measure that adds significant longevity and reliability to the roofing system.

Other situations, such as high-slope roofs, decorative roofing, or roofs with no penetration points, may not necessitate the use of underlayment. High-slope roofs may shed water effectively without it, decorative roofs might not functionally require it, and roofs without penetration points may not face the same risk of water intrusion that underlayment seeks to mitigate. Thus, the necessity for underlayment is clearly linked to conditions that increase the risk of water leaks and ice dam formation, making option B the best choice.