What Is Roofing Felt: Uses, Types, and Installation Guide

Roofing felt is a traditional underlayment material used beneath shingles and other roofing coverings to provide waterproofing, temporary protection, and a slip-resistant surface during installation. This article explains what roofing felt is, compares types, outlines installation basics, examines pros and cons, and helps homeowners and contractors make informed choices about underlayment for American roofs.

Type	Thickness/Weight	Common Use
15-pound Felt	Light, ~15 lb per 100 sq ft	Basic underlayment, low-slope or secondary protection
30-pound Felt	Heavier, ~30 lb per 100 sq ft	Primary underlayment for steeper roofs, more durable
Saturated Organic/Glass-Fiber Felt	Varies	Modern alternatives with improved tear resistance

What Roofing Felt Is And How It Works

Roofing felt, also called tar paper, is a sheet-like underlayment composed of a base material saturated with bitumen or asphalt and sometimes surfaced with mineral granules or fiberglass. Its core function is to add a layer of moisture resistance between the roof deck and the finished roofing covering. Felt helps protect sheathing during construction, acts as a secondary water barrier for shingles, and can improve fire resistance and wind uplift performance when applied correctly.

Common Types Of Roofing Felt

There are several formulations of roofing felt, with differences in base mat, saturation, and surface treatment. The main categories include organic saturated felt and fiberglass (glass-fiber) felt. Organic felt uses paper or cellulose bases saturated with asphalt, while fiberglass felt uses a glass-fiber mat for increased strength and stability.

15-Pound Vs 30-Pound Felt

15-pound felt is thinner and lighter, typically used as a temporary or budget underlayment. 30-pound felt is thicker and more durable, often specified for standard residential roofs. Building codes and shingle manufacturers sometimes require 30-pound or equivalent underlayment for warranty and performance reasons.

Synthetic Underlayments And Modified Felts

Synthetic underlayments are polymer-based alternatives offering lighter weight, higher tear resistance, and better water-shedding capabilities. Modified felts incorporate additives or fiberglass to reduce wrinkling and improve handling. While not traditional felt, these options often compete directly with felt due to performance advantages.

Primary Uses For Roofing Felt

Roofing felt serves multiple roles on a roof assembly. It acts as a temporary weather barrier during installation, a secondary moisture barrier in case shingles fail, and a protective layer that reduces abrasion between shingles and the roof deck. It also provides a safer walking surface for roofers and may serve as a vapor retarder in certain climates or assemblies.

Installation Basics And Best Practices

Proper installation of roofing felt determines much of its performance. Felt is typically rolled horizontally across the roof deck starting at the eave with a measured overhang and overlapped at horizontal and vertical seams. Fastening with cap nails or staples should follow manufacturer guidance to avoid tearing and blow-off. Ensuring correct overlaps, proper alignment, and adequate fastening prevents water intrusion and uplift during wind events.

Starter Rows, Seams, And Flashing

Begin with a starter course at the eave and continue up the roof with consistent overlaps—commonly 2 to 4 inches vertical and 4 inches horizontal for standard felt. Flashings at valleys, chimneys, and roof penetrations must be integrated with the felt to maintain a continuous water-shedding plane. Improper flashing integration is a leading cause of leaks even with quality felt installed.

Temperature And Weather Considerations

Installation in cold or hot temperatures requires care: cold felt can be brittle and tear, while hot conditions can soften asphalt-saturated felt making it stick or deform. Work windows, tactile handling, and temporary protection when storms are expected are essential to preserve felt integrity during construction.

Advantages Of Roofing Felt

Roofing felt offers cost-effective protection and a proven track record. Benefits include temporary waterproofing during construction, added secondary protection against wind-driven rain, and compatibility with most asphalt shingle systems. It also provides a familiar installation pattern for contractors and typically meets minimum code requirements for underlayment in many jurisdictions.

Limitations And Drawbacks

Traditional felt has weaknesses: it can tear or wrinkle, it may absorb moisture and become heavy, and it degrades under prolonged UV exposure. Organic felts can rot if consistently wet. Synthetics mitigate many of these issues but may cost more. Understanding the trade-offs between weight, durability, and price helps select the right underlayment for each project.

How Roofing Felt Affects Roof Lifespan And Shingle Warranties

Underlayment choice can influence shingle performance and warranty validity. Shingle manufacturers may require a minimum underlayment specification—often an equivalent to 30-pound felt or an approved synthetic product—to support full warranty coverage. A correct underlayment contributes to roof longevity by protecting decking and reducing moisture-related damage beneath the shingles.

Cost Considerations And Budgeting

Material cost for conventional felt is lower than synthetic underlayment, but labor and lifecycle costs matter. Synthetics may have higher upfront costs but can reduce installation time and offer longer service life, potentially offsetting price differences. Budgeting should account for local labor rates, roof complexity, and long-term performance expectations rather than material price alone.

Alternatives To Traditional Roofing Felt

Common alternatives include synthetic underlayments, peel-and-stick membranes, and self-adhering modified bitumen underlayment. Peel-and-stick products offer excellent adhesion and waterproofing around vulnerable areas like eaves and valleys. Choosing alternatives depends on climate, roof pitch, budget, and the desired level of moisture protection.

Maintenance, Inspection, And Longevity

Felt is not visible once shingles are installed, so preventive inspection focuses on roof coverings, flashings, and attic conditions. After storms or suspected roof damage, roofers may check for shingle loss, flashing integrity, and interior signs of leaks. When a roof is replaced, inspecting the felt can reveal prior moisture issues, rot, or inadequate installation practices.

Choosing The Right Felt For A Project

Selecting the best felt involves considering roof slope, climate, shingle manufacturer requirements, and local building codes. For steep-slope residential roofs, many professionals recommend a higher-grade 30-pound equivalent or a modern synthetic underlayment to meet durability expectations. Consulting manufacturer guides and local code officials ensures the chosen underlayment supports warranty and safety requirements.

Environmental And Safety Considerations

Traditional asphalt-saturated felt has environmental impacts related to petroleum-derived bitumen and disposal. Some synthetic underlayments offer recyclability or reduced environmental footprint. Safety during installation is also a concern because wet or wrinkled felt can create slipping hazards. Proper storage, handling, and disposal practices reduce environmental impact and worker risk.

Frequently Asked Questions About Roofing Felt

Is roofing felt required? Requirements vary by local code and shingle manufacturer; many areas require an approved underlayment. How long does it last? Felt typically lasts as long as the roof covering if kept dry and protected, but organic felt may degrade faster. Can synthetic replace felt? Yes, synthetics are commonly used as a higher-performance replacement for traditional felt.

Practical Tips For Homeowners

When hiring a roofer, request specification details for underlayment, including type, weight equivalence, and brand. Confirm that flashing and starter strips integrate with underlayment and that installers follow manufacturer installation instructions. Documenting materials and methods helps with future warranty claims and resale transparency.

Resources And Further Reading

For detailed code requirements and manufacturer instructions, consult local building departments, shingle manufacturers, and industry organizations such as the Asphalt Roofing Manufacturers Association (ARMA). Technical product data sheets and installation guides provide exact overlap, fastener, and temperature recommendations for specific felt or synthetic products.