15# roofing felt, also known as 15-pound felt, is a lightweight underlayment used in asphalt shingle roofing systems. It provides a temporary weather barrier, helps protect sheathing during installation, and aids in moisture management before shingles are fully installed. This guide explains what 15# felt is, when to use it, installation steps, tools, performance, limitations, and best practices to ensure a durable, cost-effective roof underlayment for a variety of American climates.
What Is 15# Roofing Felt
15# roofing felt is a bitumen-saturated kraft paper or fiberglass-reinforced material rated at 15 pounds per 100 square feet, indicating its weight and density. It is designed to shed light moisture and protect the roof deck during construction and in mild weather conditions. Compared with higher-weight underlayments, 15# felt is lighter, easier to handle, and less expensive, making it common on standard-residential roofs. It is compatible with most asphalt shingles and works well as a secondary moisture barrier when installed correctly.
When To Use 15# Felt
15# felt is appropriate for dry or mildly damp climates and as a temporary weather barrier during construction. It is often used on roofs with asphalt shingles where tar paper is not required to be a long-term barrier. In regions with heavy rainfall, snow, or high humidity, builders may opt for heavier underlayments (such as 30# or synthetic) for enhanced protection. Local building codes or manufacturer specifications should guide whether 15# felt is acceptable for a given project.
Installation Basics
Proper installation ensures that 15# felt performs as intended. Start at the eave edge, unrolling the felt with the sticky or tabbed side facing down if applicable. Align to the rafters and overlap edges by a standard amount, typically 2 to 4 inches, depending on local code and weather conditions. Use corrosion-resistant nails or staples to secure the felt, placing fasteners about every 8 to 12 inches along seams and edges. Ensure there are no large wrinkles and that all seams are overlapped in the correct direction to prevent wind-driven uplift.
Weather considerations matter. Do not install 15# felt in high wind or rain; moisture can compromise the felt and reduce bond strength. When working under cold temperatures, allow for extra overlap and avoid stretching the material. Maintain a clean surface on the roof deck to ensure good adhesion and a snug fit around penetrations like chimneys or vents.
Tools And Materials
- 15# Roofing Felt Roll
- Roofing nails or staples (galvanized or corrosion-resistant)
- Hammer or nail gun
- Utility knife or scissors for trimming
- Measuring tape and chalk line
- Roofing adhesive or mastic (if required by code or manufacturer)
- Chalk line for straight alignment
Choosing the right fasteners and ensuring compatibility with local codes is essential. Some installers prefer staples for synthetic underlayment, but for paper-based felt, nails are often recommended to minimize tearing in windy conditions. Read the manufacturer’s installation guidelines to confirm fastener type, spacing, and overlap requirements.
Performance And Limitations
15# felt offers a basic moisture barrier during construction and a temporary shield against weather. It provides a helpful layer between the roof deck and shingles, supporting insulation and helping with debris containment. However, its performance is limited by climate and exposure time. Prolonged moisture exposure, wind uplift, or heavy snow can degrade the felt and compromise its protective function. It is not a substitute for a high-grade synthetic underlayment or a fully sealed roofing system in harsh environments.
The lifespan of 15# felt depends on installation quality, weather exposure, and roof slope. On steeper roofs with proper flashing and ventilation, it may perform adequately for the construction window or a short-term period. For longer-term protection, especially in regions with frequent precipitation, consider upgrading to a heavier underlayment or a synthetic option that resists tearing and provides better water resistance.
Care, Maintenance, And Replacement
After installation, inspect the underlayment for tears, loose edges, or exposed fasteners after storms or high winds. If damage is found, repair or replace the affected area promptly to maintain a continuous barrier. When preparing for roof replacement or significant repairs, recognize that 15# felt typically has a finite life and may need replacement during or after the project.
Before finalizing the roof, ensure proper ventilation and drainage to minimize moisture accumulation under the underlayment. If leaks are suspected or moisture intrusion occurs, address the source, such as flashing defects or missing shingles, and re-evaluate the underlayment’s condition. Proper disposal of damaged or expired felt should follow local regulations, and recycling options may be available in some areas.
Environmental Considerations And Disposal
15# roofing felt is commonly made from asphalt-saturated paper, which has environmental implications if discarded improperly. When possible, dispose of damaged material through local construction waste programs that handle asphalt products. Some regions offer recycling or energy recovery options for asphalt-containing building materials. Consider minimizing waste by measuring accurately and planning the project to reuse rolls where feasible and safe.
Emerging alternatives, such as synthetic underlayments, provide higher tear resistance and better long-term moisture protection. If environmental impact or long-term performance is a priority, evaluating these options against 15# felt can guide a more sustainable choice for a given project.