Building Paper vs Roofing Felt: What Homeowners Need to Know

The choice between building paper and roofing felt is a common decision in home improvement projects. Both materials act as protective underlayment, shielding roofs and walls from moisture during installation and over time. Understanding their differences, installation requirements, and best-use scenarios helps homeowners select the right product for durability, code compliance, and budget. This article compares building paper and roofing felt in terms of composition, performance, installation, and practical applications to guide informed decisions.

What Each Material Is And How It Is Made

Building paper is a generic term for a variety of paper-based underlayments used beneath roofing layers on walls and roofs. It includes options like asphalt-saturated felt, plain paper, and moisture barriers. Roofing felt, often referred to as felt paper, is a specific type of asphalt-impregnated material designed to shed water and provide a temporary weather-resistant barrier during construction. Both products traditionally come in rolls and are installed in overlapping courses to create a continuous surface.

Key distinction: Roofing felt typically contains asphalt and fiberglass or organic fibers for enhanced waterproofing and durability, while building paper may rely more on fiber content and sizing without asphalt in some variants. This difference influences tear resistance, weather resistance, and long-term performance.

Performance And Weather Protection

Roofing felt generally offers superior weather protection due to asphalt saturation, which provides a waterproof layer during rain in construction. It acts as a barrier against wind-driven moisture and helps protect the roof deck before shingles are applied. Building paper can provide a basic moisture barrier but may not offer the same level of waterproofing, especially in exposed or prolonged wet conditions. The specific grade, weight, and asphalt content determine how well each material stands up to moisture exposure.

In terms of UV exposure, roofing felt is designed to tolerate some sun during installation, but most underlayments require protection soon after application. Building paper may degrade more quickly in direct sunlight if not protected by the final roofing materials. For walls, water-resistive barriers using building paper variants are common in older homes, while newer systems favor integrated WRB (water-resistive barrier) membranes with higher permeability and air control.

Weights, Strength, And Durability

Underlayment weight is a practical indicator of strength. Roofing felt is often labeled by weight per square (e.g., 15#, 30#) or by metric equivalents, with higher numbers indicating thicker, tougher material. Heavier roofing felt resists tearing during installation and provides longer-lasting protection against wind-driven moisture. Building paper weights vary widely, from lighter mats to heavier asphalt-impregnated sheets. Generally, roofing felt offers greater puncture and tear resistance, which is important when workers walk on the surface during installation or maintenance.

Durability also depends on exposure time. Roofing felt is designed to remain in place beneath shingles or other coverings until the final roofing is installed, at which point the final layers take over waterproofing. Building paper, when used on walls, typically accompanies a more comprehensive wall assembly where the WRB system is specified to balance moisture management and structural integrity.

Installation Guidelines And Best Practices

Installation practices differ for roofs and walls. For roofing, felt is installed with overlapping horizontal courses, typically starting at the eave and working upward. Fasteners or adhesives secure the felt, and each sheet overlaps the previous one to shed water toward the outside. The final roofing material (shingles or metal) provides primary protection, while felt acts as a temporary shield during construction. It is essential to follow manufacturer guidelines for overlap width, nailing patterns, and exposure allowances.

For walls, building paper often serves as the moisture barrier beneath siding or other exterior claddings. In many jurisdictions, building paper is used in conjunction with a dedicated WRB system that includes additional drainage planes and taping at seams and joints. Proper sealing at corners, window openings, and roof-to-wall interfaces is critical to prevent moisture intrusion. Contractors should verify compatibility with the chosen siding, wrap, and fastener types to ensure effective performance.

Code Compliance And Best-Use Scenarios

Local building codes typically specify acceptable underlayment materials for roofs and walls. Roofing felt has long been a standard in many regions, with requirements for asphalt-saturated felt or synthetic underlayment based on climate and roof pitch. Modern building codes increasingly favor synthetic underlayments that offer similar or superior performance with improved durability, reduced weight, and easier installation. When choosing between building paper and roofing felt, homeowners should consult local code requirements and project specifications.

Best-use scenarios include roofing systems that require a traditional felt layer for temporary protection during shingle installation, or walls in regions where a basic moisture barrier is sufficient within a modern WRB system. For new builds or extensive remodels, synthetic underlayments and advanced WRB systems may provide better long-term performance, energy efficiency, and air barriers. The choice should balance cost, expected exposure, and maintenance plans.

Cost Considerations And Longevity

Cost differences between building paper and roofing felt can influence project decisions. Roofing felt tends to be more expensive per square foot than basic building paper, but its durability and weather protection can reduce the risk of moisture-related damage during construction. Long-term longevity is more strongly influenced by the overall roof assembly and climate exposure than by underlayment alone. In wall applications, the cost of a comprehensive WRB system may be higher upfront but can improve energy efficiency and moisture control over time.

Maintenance considerations include inspecting for any damage after storms or heavy winds and ensuring proper overlap and sealant at seams. In regions with high wind or heavy rainfall, higher-performance underlayments or synthetic WRB layers may offer better long-term protection and fewer maintenance requirements.

Practical Quick-Reference Guide

• Roofing use: Roofing felt provides temporary waterproofing during shingle installation; choose appropriate weight (e.g., 15# to 30#) or synthetic alternatives based on climate and roof design.
• Wall use: Building paper serves as a basic moisture barrier; for enhanced performance, pair with a full WRB system designed for siding and climate.
• Weather exposure: Roofing felt resists moisture during construction but may degrade under prolonged sun exposure; synthetic underlayments offer longer life.
• Code and compatibility: Always verify local code requirements and ensure compatibility with roofing materials, siding, and fasteners.

In summary, roofing felt and building paper serve related but distinct roles in building envelopes. Roofing felt is optimized for temporary roof protection and moisture management during installation, with greater durability under wind and rain exposure. Building paper, when used on walls, functions within broader WRB systems to manage moisture and provide air control. Homeowners should align material choices with local codes, climate conditions, and the overall design of the exterior envelope. When in doubt, consult a licensed contractor or building official to select the most appropriate underlayment for the project.