Rolls of Roofing Felt: Types, Installation and Tips

Roofing felt rolls are a foundational material used to provide a weather-resistant underlayment for roofs. They help protect sheathing from moisture during construction and offer a secondary barrier against leaks once the roofing system is in place. This article explains what roofing felt rolls are, the main types and weights, how to choose the right roll, installation steps, benefits and limitations, maintenance, and common troubleshooting tips.

What Are Roofing Felt Rolls?

Roofing felt rolls are sheets of asphalt-impregnated material or synthetic polymer designed to act as an underlayment beneath shingles, tiles, or metal roofs. They come in widths typically ranging from 36 inches to 54 inches and in various weights or grades that indicate durability and tear resistance. Felt rolls can be traditional organic felt (cellulose fibers coated with asphalt) or modern synthetic felts that use fiberglass or polyester fabric bonded with asphalt or polymer compounds.

Types And Weights

The choice of roofing felt depends on climate, roof design, and local building codes. The two broad categories are organic asphalt-saturated felt and synthetic underlayments. Each category includes several weights or grades that reflect thickness and puncture resistance.

• Organic Roofing Felt (No. 15, No. 30): Made from cellulose fibers saturated with asphalt. It is traditional, inexpensive, and commonly used on older or low-slope roofs, but it is more susceptible to moisture and tearing compared with modern synthetics.
• Asphalt-Saturated Felt: A general term for felt impregnated with asphalt, offering durability suitable for many installations but sometimes limited by temperature sensitivity in extreme heat or cold.
• Synthetic Roofing Underlayment: Made from synthetic fibers such as fiberglass or polypropylene, often reinforced for strength and tear resistance. They are lighter, more durable, and perform well in a range of weather conditions.
• Weight Classes: Common weights include light (around 30-lb per 100 sq ft), medium (40-60 lb per 100 sq ft), and heavy (80 lb per 100 sq ft) depending on the product. Higher weights generally provide better puncture resistance and longer life but may be harder to handle.
• Self-Adhering Underlayments: Feature a pressure-sensitive adhesive layer on one side, offering a fast, water-tight seal with fewer fasteners. They are popular in cold climates and for roofs needing quick weatherproofing.

How To Choose Roofing Felt Rolls

Choosing the right felt involves climate, roof pitch, and installation method. In general, synthetic underlayments have risen in popularity due to durability and lighter weight, while organic felts may be chosen for budget-conscious projects or where code allowances permit.

• Climate And Slope: Steeper roofs and areas with heavy rainfall benefit from synthetic felts or self-adhering underlayments that improve water shedding and seal integrity.
• Roof Covering Compatibility: Some shingles or tiles require specific underlayment types. Always check manufacturer guidelines for compatibility.
• Local Codes: Municipal or state codes may specify min/max underlayment performance or installation methods.
• Durability Needs: For long-term moisture protection and ease of installation, synthetic felt with a high puncture resistance rating is often preferred.
• Installation Environment: In cold climates, self-adhesive or cold-applied underlayments can simplify installation and improve sealing.

Installation Essentials For Roofing Felt Rolls

Proper installation is crucial to ensure the underlayment performs as intended. Following manufacturer instructions and local building codes helps prevent common failures.

• Surface Preparation: Clean the roof deck, remove protruding nails, and repair any damaged boards. The surface should be dry, smooth, and free of sharp edges.
• Roll Alignment: Start at the eave edge and unroll across the roof, ensuring the felt lies flat with no wrinkles. Overlap courses typically range from 2 inches on standard or self-adhering underlayments to 4 inches for some traditional felts.
• Sealing And Fastening: For non-self-adhering felts, use galvanized or corrosion-resistant nails with caps to secure the sheet at regular intervals. Do not drive nails too close to edges to avoid tearing.
• Sealing Seams: Overlaps should be tight and straight. For self-adhering options, back off the release paper gradually to prevent air bubbles and ensure a smooth seal.
• Roof Penetrations: Cut openings precisely around chimneys, vents, and skylights, and use appropriate flashing or gaskets to maintain a continuous water barrier.

Benefits And Limitations

Understanding the trade-offs helps homeowners and builders select the right product for the project.

• Benefits: Provides a secondary moisture barrier, reduces wind-driven moisture intrusion, distributes minor surface irregularities, and protects the roof deck during construction.
• Limitations: Organic felts are less durable in wet conditions and can deteriorate over time. Synthetic underlayments may have higher upfront costs. Some underlayments require careful installation to prevent wind uplift in high-wind areas.

Maintenance And Longevity

Underlayment visibility is limited after the roof is installed, but maintenance focuses on overall roof health and timely replacement when signs of wear appear.

• Inspection During Maintenance: Check for exposed or damaged areas following major storms. Look for tears, punctures, or lifted edges, especially around penetrations and edges.
• Replacement Triggers: Significant tearing, moisture staining, or bulges indicate replacement may be necessary to preserve roof integrity.
• Impact Of Time: Even well-installed underlayments have a limited lifespan. Standard synthetic underlayments often last 20–40 years depending on climate, roof type, and exposure.
• Limitations On Durability: They are not a substitute for a complete roof system; proper installation and compatible roofing material are essential for long-term performance.

Common Mistakes And Troubleshooting

Awareness of typical issues helps avoid costly repairs or leaks later in the roof’s life.

• Poor Overlap And Fastening: Insufficient overlaps or missed fasteners can create gaps, allowing water intrusion and wind uplift.
• Improper Sealing At Penetrations: Inadequate flashing or misaligned seams around vents and chimneys increases leak risk.
• Moisture During Installation: Installing felts on damp decks can trap moisture and promote mildew or adhesive failure.
• Incompatible Materials: Using underlayment mismatched with shingles or tiles can reduce performance and warranty coverage.