Difference Between 15 and 30 Roofing Felt: What Builders Need to Know
Roofing felt acts as a secondary weather barrier beneath shingles, providing temporary protection and helping to manage moisture. The choice between 15-pound and 30-pound roofing felt affects tear resistance, durability, and installation practices. Understanding the differences helps builders meet code requirements, optimize performance, and control costs. This article compares 15 and 30 roofing felt across material properties, typical applications, installation considerations, and practical guidance for common roof types in the United States.
What Roofing Felt Is
Roofing felt, also called underlayment, is a paper-like or synthetic layer installed between the roof deck and the final shingle or tile. It offers secondary protection against wind-driven rain, helps with seam sealing, and provides a smoother surface for shingles to lay on. Felt comes in varying weights, commonly described as pounds per 100 square feet (lb/100 ft²). Heavier felts generally provide greater tear resistance and durability during installation and weather exposure.
Understanding 15- And 30-Lb Felt
15-lb felt and 30-lb felt refer to builder-grade asphalt-saturated paper or equivalent synthetic underlayment products. The 15-lb version is lighter, easier to handle, and typically cheaper, but offers less tear resistance and durability. The 30-lb version is heavier, more robust, and more resistant to damage during roofing work and in adverse weather. In many markets, 30-lb felt may meet or exceed certain code requirements for roof underlayments in specific climate zones or roof types.
Applications And Building Codes
The suitability of 15-lb vs 30-lb felt depends on roof slope, climate, and local building codes. In dry or moderate climates with simple roof pitches, 15-lb felt may suffice as a secondary barrier when complemented by proper shingle installation. In harsher climates, high-wind regions, or steeper roofs, 30-lb felt is often recommended or required due to its improved tear resistance and puncture resistance. Some jurisdictions specify underlayment requirements for new construction or re-roofing projects, and these rules may favor heavier underlayments for enhanced protection against wind-driven rain and ice dams.
Performance And Durability
Key performance factors include tear strength, puncture resistance, water resistance, and adhesion. 30-lb felt generally offers better tear resistance, reduces the risk of exposing the roof deck during installation, and tends to perform better in windy conditions. Both products are designed to shed water, but heavier felt maintains integrity longer when exposed to weather before shingles are installed. Synthetic underlayments, though not the focus here, may provide superior performance and a different weight rating, sometimes replacing traditional felt entirely in certain markets.
Installation Considerations
Installation practices influence performance as much as material choice. With 15-lb felt, careful handling is important to prevent tears during layout and nailing. Nails or staples should be placed per manufacturer guidance to avoid tearing. 30-lb felt can tolerate more handling roughness and may be less prone to damage when courses overlap and align. Roof slope, deck condition, and ventilation also affect underlayment performance. Proper overlapping, fastener placement, and alignment with drip edge and flashing are essential for both weights to maximize moisture control.
Impact On Cost And Availability
The cost gap between 15-lb and 30-lb felt typically reflects the material weight, tear resistance, and durability. 30-lb felt tends to be more expensive per square foot but may reduce labor costs by withstanding installation wear and minimizing repairs. Availability varies by region and supplier, with some markets offering more synthetic or premium underlayment options. Builders should balance upfront material costs with expected performance, climate considerations, and local code requirements to determine the most cost-effective choice.
Quick Comparison Table
| Factor | 15-Lb Felt | 30-Lb Felt |
|---|---|---|
| Weight | Approximately 15 lb per 100 ft² | Approximately 30 lb per 100 ft² |
| Tear Resistance | Lower | Higher |
| Puncture Resistance | Lower | Higher |
| Wind & Weather Durability | Moderate | Better |
| Installation Ease | Easier to handle | Heavier to handle |
| Typical Use | Moderate climates, standard roofs | |
| Code Considerations | Depends on locality | Often preferred or required in harsher climates |
| Cost | Lower | Higher |
Tip: Always consult local building codes and manufacturer instructions for underlayment requirements, as some regions mandate heavier underlayments or synthetics for new constructions or re-roofs.