Putting Down Roofing Felt: A Complete Guide

Putting down roofing felt is a foundational step in many roofing systems, providing an extra layer of weather resistance and a stable surface for shingle installation. This guide covers material choices, preparation, proper installation techniques, overlaps, fasteners, and maintenance. Read on to understand best practices for American roofs and how to maximize the effectiveness of roofing felt as underlayment.

Planning And Materials

Choosing the right roofing felt begins with understanding the roof type, climate, and local building codes. In the United States, common options include asphalt-saturated felt and self-adhering membranes. Asphalt-saturated felt is economical and familiar to many contractors, while self-adhering underlayments provide superior adhesion and better wind resistance in exposed areas. Determine the correct weight (commonly 15-pound or 30-pound felt) and consider climate factors such as heavy rain, snow, and UV exposure when selecting the product.

Key materials include:

• Roofing felt rolls (asphalt-saturated or self-adhering)
• Roofing nails or staples appropriate for felt and deck
• Sealant or flashing tape for edges and penetrations
• Chalk line, utility knife, and scissors for cutting
• Roofing cement or sealant for seams and repairs
• Safety gear: gloves, eye protection, non-slip footwear

Ensure access to a clean, dry, and sunlit working area on the roof for accurate alignment and trimming. Having a partner can help manage long rolls and maintain consistent overlap.

Preparation Of The Roof Deck

Proper deck preparation ensures the felt adheres and performs as intended. Inspect the roof to remove debris, protruding nails, and damaged boards. If there is any moisture or rot, address it before applying underlayment. The deck should be dry and smooth, with any rough edges planed or cut flush.

For asphalt-saturated felt, lay a clean surface that is free of oil and dust. For self-adhering membranes, ensure the deck surface is dry and free of dust or moisture traps to promote proper bonding. In some climates, a new layer of roof felt can also help extend the life of existing shingles by providing an additional moisture barrier at the deck level.

Step By Step Installation

The installation sequence varies slightly between felt types, but core principles remain the same: maintain alignment, ensure proper overlaps, and secure the material without tearing it. The following steps outline a typical process for asphalt-saturated felt used as underlayment beneath asphalt shingles.

• Begin at the eave: Unroll the first strip along the roof edge, aligning with the drip edge.
• Overlap direction: Roll out with a 2- to 4-inch horizontal overlap (check local code). For self-adhering underlayment, follow manufacturer guidelines for overlaps and bond.
• Fastening: For non-self-adhering felt, secure with roofing nails or staples every 8–12 inches along the sheet, taking care not to puncture the leather or paper layer excessively. For self-adhering felt, press firmly to activate the adhesive; no nails are needed except at edges or overlaps as specified.
• Seams: Ensure seams are fully overlapped and flat. Avoid wrinkles or air pockets that can trap moisture.
• Edge details: Extend the felt a few inches over the drip edge at the eaves and secure along rake edges to prevent wind uplift.
• Penetrations: Use flashing and sealant at vents, chimneys, and skylights; cut holes slightly smaller than the pipe or fixture and seal with compatible sealant.
• Inspection: After installation, walk the roof gently to verify adherence and identify loose sections or lifted corners.

When working with large rolls, plan a practical working width to minimize stepping on unfastened areas. Maintain a steady pace to keep the material from wrinkling and to ensure consistent adhesion in self-adhering products.

Overlaps And Fastening

Overlaps are critical for weatherproofing. Insufficient overlap can allow water to seep under the underlayment, while excessive overlap wastes material. A common rule is a 2–4 inch horizontal overlap for asphalt-saturated felt, with vertical overlaps of 4–6 inches where required by climate and code.

Fastening patterns differ by product. Asphalt-saturated felt typically uses nails or staples along the edges and at intervals across field sections. Self-adhering membranes rely on adhesive bonding and, where specified, may require light rolling with a hand roller to ensure good contact. In windy regions, additional fasteners or edge sealing may be necessary to prevent lift.

For edge seals and terminations, use compatible sealant or flashing tape to secure the perimeter and around penetrations. Inspect overlaps after installation and re-secure any lifted areas promptly to maintain a continuous moisture barrier.

Inspection And Maintenance

Post-installation inspection helps verify the underlayment’s effectiveness. Check for tears, wrinkles, or air pockets, especially near eaves, rakes, and along hips. If using self-adhering underlayment, ensure no gaps exist where the adhesive didn’t fully bond. Maintain the deck by removing debris that could compromise the felt’s performance before shingles are applied.

Seasonal maintenance is advisable. In areas with freeze-thaw cycles, inspect for any moisture intrusion after heavy rain or snowmelt. Address damaged sections promptly by reapplying new felt or sealing with appropriate materials. If a roof is re-roofed, determine whether reusing old felt is acceptable or if a full replacement is recommended by local building codes.

Safety Considerations

Roof work carries fall hazards. Use a proper fall protection plan, including harnesses, guardrails, or rope systems where required by code. Wear non-slip footwear and work with a partner when handling long rolls to prevent slips or accidental drops. Keep a tidy workstation on the roof to minimize tripping hazards, and follow manufacturer guidelines for product installation and handling. Weather conditions, such as wind or rain, can affect application; avoid installation during adverse weather to reduce risk and ensure effective adhesion.