Putting Down Roofing Felt: A Practical Guide for Homeowners

Putting down roofing felt, or roof underlayment, is a crucial step in protecting a home from moisture and weather while providing a stable surface for shingles. This guide explains how to prepare, select the right felt type, and install the underlayment for a durable roof. Accurate installation reduces leaks, extends roof life, and helps meet building code requirements. Readers will learn practical steps, safety tips, and common mistakes to avoid during the process.

Tools And Materials

Having the right tools makes the installation efficient and accurate. Essential items include:

• Roofing felt (poly-felt or asphalt-saturated felt) in the appropriate weight for the roof type
• Sharp utility knife or scissors
• Hammer or staple gun (as required by felt type)
• Roofing nails or staples, depending on the underlayment
• Chalk line and measuring tape
• Ladder, safety harness, and non-slip shoes
• Roofing cement or sealant for seams and penetrations
• Tin snips for trimming

Selecting the correct underlayment material is critical. Standard #15 or #30 asphalt-saturated felt provides durability and moisture resistance. In areas with severe weather or high wind, self-adhering roofing underlayment offers improved leak protection. Always verify product specifications with the manufacturer and align with local building codes.

Types Of Roofing Felt

Understanding the main categories helps choose the right product for a given roof. The two common types are:

• Asphalt-saturated felt: A traditional underlayment made from asphalt-impregnated kraft paper or fiberglass mat. It is cost-effective and suitable for many climates when installed correctly.
• Self-adhering (rubberized asphalt) underlayment: Features a self-adhesive layer protected by a release film. It provides excellent seal against moisture and is favored in high-wind or leak-prone areas.

Some regions require or recommend moisture barriers or synthetic underlayments, which offer higher tear resistance and faster installation. Always consider climate, roof pitch, and shingle type when selecting underlayment.

Preparation

Proper preparation ensures the felt lays flat and seals properly. Steps include:

• Repair damaged sheathing, replace rotten boards, and ensure decking is dry and clean.
• Remove old felt and debris from the roof surface if replacing an existing layer.
• Check local codes for underlayment requirements, including perimeters and eave protection.
• Measure the roof and plan the installation pattern to minimize waste and maximize overlap.

Weather considerations matter. Install felt on dry, mild days. Wet or freezing temperatures hinder adhesion and fastening. Allow windows or vents to remain closed to prevent moisture buildup inside the attic during work.

Installing Roofing Felt

The installation process varies slightly by product, but general principles apply. Follow these steps for asphalt-saturated felt or synthetic underlayment:

• Start at the bottom: Roll out the first row along the eave with the gapped edge pointing upward to establish a uniform starter row.
• Overlap: For traditional felt, provide a minimum 2-inch (5 cm) vertical overlap between sheets and a 4 to 6 inch (10 to 15 cm) horizontal overlap, depending on product instructions. Self-adhering membranes require careful alignment and tab removal as you progress.
• Securing: Use roofing nails or staples along the edges and at regular intervals per the manufacturer’s recommendations. Do not overdrive fasteners; keep them flush with the surface.
• Seams and overlaps: Seal overlaps with appropriate sealant or self-adhesive tape if needed. Special attention is needed around roof penetrations, chimneys, and skylights to prevent moisture entry.
• Continuing up the slope: Work upward in a consistent pattern, ensuring each course overlaps the previous one as specified.
• Ventilation and eaves: Maintain proper eave protection as required by code, especially in cold climates where ice dams are a concern.

For roofs with steep pitches, consider using fall protection and a helper to handle large sheets. Some synthetic underlayments allow fast installation with simple roofing nails, while self-adhering products may require more care to avoid air pockets.

Overlaps, Seams, And Fastening Details

Correct overlap and fastening choices are essential for a durable roof underlayment. Key points include:

• Overlap requirements: Follow the manufacturer’s guidance. Typical overlaps range from 2 to 6 inches, depending on product and climate.
• Sealing: Ensure all seams are well-sealed, particularly in areas with strong winds or heavy rainfall. Self-adhering products often include a film that must be peeled away gradually to activate the adhesive.
• Fastening pattern: Space nails or staples evenly along the edges and at intervals within the field. Avoid tearing the material with over-tightening.
• Edge protection: Pay extra attention to eaves and rakes where wind uplift is greater. Some installations require metal drip edge over the felt for added protection.

When in doubt, consult the product guidelines and local building codes. Proper installation reduces the risk of moisture intrusion and extends roof life.

Common Mistakes And Pro Tips

Avoidable errors can compromise performance. Common mistakes include:

• Installing on wet decking or in freezing conditions
• Using too few fasteners or improper fastening patterns
• Failing to correct irregularities in the roof surface before laying felt
• Neglecting to seal around penetrations or at eaves and rakes

Pro tips: Pre-cut sheets to fit the roof layout, reduce waste, and keep nails per instructions. Use chalk lines to maintain straight courses and finish with a clean edge along ridges and hips. If using self-adhering underlayment, ensure the surface is clean and dry before application to optimize adhesion.

Maintenance And Replacement Considerations

Roof underlayment is not permanent. Regular inspections after heavy weather can identify damage or gaps. If the felt shows signs of tearing, peeling edges, or moisture intrusion, replacement or repair is necessary. In reroof projects, consider upgrading to a synthetic or self-adhering underlayment for added durability and improved performance in challenging climates. When planning long-term maintenance, factor in climate conditions, roof pitch, and shingle compatibility to determine optimal underlayment choices.

Keeping accurate records of installation dates and materials used helps with future maintenance and resale value. For homeowners tackling this task, adhering to manufacturer guidelines and local codes ensures a successful, long-lasting roof underlayment that provides effective moisture protection.