The Role of Underlayment in Roofing Systems
A roofing system is comprised of more than just the outer materials that are visible from the street, such as shingles or tiles. Beneath these outer layers lies a critical component known as underlayment. This article explains the purpose, types, and importance of underlayment in roofing systems, offering homeowners insights into how it helps protect their homes.
What is Roofing Underlayment?
Roofing underlayment is a layer of material installed between the roof deck (the structural surface beneath the outer roofing material) and the visible roofing materials like shingles, tiles, or metal. It serves as an additional barrier that protects the roof deck from moisture, weather, and other external elements that can cause damage.
Functions of Roofing Underlayment
Moisture Protection: The primary function of roofing underlayment is to provide a secondary barrier against water that penetrates the outer roofing material. This is crucial because even small amounts of moisture can damage the roof deck, leading to mold, rot, and other structural issues over time.
Weather Barrier: Underlayment also serves as an added layer of protection against wind-driven rain, snow, and ice. In extreme weather conditions, it can prevent water infiltration that might occur due to damaged shingles or tiles.
Vapor Barrier: Some types of underlayment also act as vapor barriers, helping to minimize the risk of condensation in the attic space that can lead to mold growth and decreased indoor air quality.
Provides a Smooth Surface: Underlayment helps create a flat, uniform surface over the roof deck, which can enhance the appearance of the finished roof by preventing irregularities from showing through.
Types of Roofing Underlayment
Felt Underlayment (Asphalt-Saturated Felt): Traditionally used underlayment made from natural fibers or synthetic materials soaked in asphalt. It is available in two thicknesses: #15 and #30 (with #30 being thicker and more durable).
Synthetic Underlayment: Made from polypropylene, fiberglass, or polyester, synthetic underlayment is lighter, stronger, and often more durable than felt. It is also resistant to mold and water, and some types are designed to be vapor permeable.
Rubberized Asphalt Underlayment: This type features higher percentages of asphalt and rubber polymers, making it waterproof. It often comes with a self-adhesive backing that seals to the roof deck, providing excellent protection against water and air infiltration.
Installation Considerations
Proper installation of roofing underlayment is crucial for its effectiveness. The method of installation may vary depending on the type of underlayment and the roofing materials used. Key considerations include:
Overlap: Underlayment sheets should overlap to ensure complete coverage and prevent leaks. The amount of overlap can depend on the slope of the roof and the type of underlayment.
Fastening: Proper fastening is crucial to prevent the underlayment from being torn or blown away before the outer roofing material is installed. The type of fasteners and the spacing between them can vary based on the underlayment material and local building codes.
Sealing: Joints and seams should be properly sealed, especially if using water-resistant or waterproof underlayment, to prevent water ingress.
Conclusion
Roofing underlayment is a vital component of any roofing system. It not only acts as a secondary barrier against moisture and weather but also contributes to the overall durability and longevity of the roof. Choosing the right type of underlayment and ensuring it is properly installed are critical steps in protecting your home from the elements and enhancing the performance of your roof. Homeowners should consult with professional roofing contractors to select the best underlayment for their specific roofing materials and climate conditions.
