Meta Description: Learn what roofing felt paper rolls are, how 15-pound and 30-pound felt differ, where they’re used, and how to install and store them.
A roll of felt paper is a familiar sight on roofing jobs, but the product’s name can be confusing. In the United States, it usually refers to asphalt-saturated roofing felt: a water-resistant underlayment installed between a roof deck and shingles or other roofing materials. Felt can help protect a structure from moisture during construction and provide a secondary layer beneath the finished roof. Choosing the right roll involves more than comparing price or weight; roof slope, climate, roofing material, and local code requirements all matter.
What Is a Roll of Felt Paper?
Roofing felt is a flexible sheet made from a fibrous base, commonly cellulose or a synthetic fiber, saturated or coated with asphalt. It is supplied in rolls and installed in overlapping courses across a roof deck. The felt is not the finished roof and is not intended to serve as a permanent, exposed weather barrier. Instead, it is one component in a complete roofing system.
People may also call it tar paper, roofing felt, or felt underlayment. The terms are often used interchangeably at hardware stores, although product formulations and performance can differ. “Tar paper” is a traditional name; modern roofing felt is generally asphalt-based rather than made with coal tar.
Felt paper can also refer to other construction or craft papers. In roofing discussions, however, a “roll of felt paper” most often means asphalt roofing underlayment. Product labels should be checked to confirm intended use, specifications, and compatibility with the roofing system.
What Roofing Felt Does
Roofing felt provides a secondary layer of water-shedding protection beneath shingles, tiles, or other roof coverings. If wind-driven rain or melting snow gets past the outer roofing material, properly installed underlayment can help limit water reaching the roof deck. It also helps protect the deck from weather during the period between installation and completion of the roof, subject to the product’s exposure limits.
Felt can help separate roofing materials from the roof deck and may reduce direct contact between wood and the roof covering. It does not make a roof waterproof by itself. Flashing, properly installed roof coverings, valley details, ventilation, and sound deck construction remain essential.
Roofing felt is not a substitute for ice barriers where those are required, nor is it a substitute for a vapor retarder or an interior moisture-control strategy. These products address different parts of a building’s moisture-management system.
Common Felt Paper Types and Weights
Roofing felt is commonly sold in nominal 15-pound and 30-pound grades. The names refer to historical weight classifications, not necessarily the exact weight of every modern roll. Product standards and manufacturing methods have changed, so the label’s stated coverage and specifications are more useful than assuming a precise weight from the grade name alone.
| Type | Typical characteristics | Common considerations |
|---|---|---|
| 15-pound felt | Generally lighter and easier to handle than heavier felt | Often used beneath asphalt shingles when permitted by the product instructions and local requirements |
| 30-pound felt | Generally heavier and more robust to handle | May be selected for certain applications or roofing systems; check the roof-covering manufacturer’s requirements |
| Synthetic underlayment | Made from woven or nonwoven synthetic materials rather than traditional asphalt-saturated felt | Often lighter per unit of coverage and may offer different tear, traction, or exposure characteristics |
| Self-adhered underlayment | Has an adhesive backing and is commonly used for specific water-management details | May be specified at eaves, valleys, or other areas; installation and substrate requirements vary |
Some manufacturers use product names such as “No. 15” or “No. 30,” while others describe a product by its intended use or performance. These labels should not be treated as universal guarantees of suitability. Always consult the product data sheet and the roofing-material manufacturer’s instructions.
Roll Sizes and Coverage
Roofing felt rolls come in different widths, lengths, and stated coverage areas. A common traditional roll is about 36 inches wide, but dimensions vary by manufacturer and product. Coverage also depends on the required overlap and the shape of the roof. A roll’s nominal square footage is not the same as the area it will cover after installation.
To estimate how much roofing felt is needed, start with the roof area rather than the home’s floor area. A simple gable roof has two sloped surfaces; hips, dormers, valleys, and other features increase the actual area and can create more cutting waste. Roof pitch also affects the relationship between a building’s footprint and its sloped roof surface.
- Measure or obtain the roof’s total surface area.
- Check the roll label for its stated coverage and installation overlap instructions.
- Account for valleys, ridges, hips, penetrations, and cutting waste.
- Compare the product’s coverage with the local code and roofing manufacturer’s requirements.
Contractors often estimate material in “squares,” a roofing term for 100 square feet of roof area. A bundle or roll’s coverage varies by product, so the label—not a general rule of thumb—should guide purchasing. For complicated roofs, a roofing professional can calculate the order more reliably.
Where Felt Paper Is Used
Under Asphalt Shingles
Traditional felt has long been used as underlayment beneath asphalt shingles. Whether a particular felt product is appropriate depends on the shingle manufacturer’s instructions, roof design, and applicable building code. Some systems allow or specify synthetic underlayment, while others may require particular materials or installation methods.
Under Other Roof Coverings
Underlayment requirements differ for metal roofing, wood shakes, tile, and other roof coverings. The materials can respond differently to heat, movement, and moisture, so a felt product acceptable beneath shingles may not be appropriate for another covering. The roofing manufacturer’s installation manual is the best starting point.
Temporary Weather Protection
Felt can protect a roof deck temporarily while the roofing work is in progress, but it should not be assumed to provide indefinite exposure protection. Sun, wind, rain, foot traffic, and temperature can affect the material. Product labels specify exposure limits, and the roof covering should be installed within the stated period.
How Roofing Felt Is Installed
Installation begins with a clean, dry, structurally sound roof deck. Damaged or protruding material should be addressed before underlayment is applied. The felt is typically laid in horizontal courses, starting at the eaves and moving upward toward the ridge, so upper courses overlap lower ones and shed water toward the eaves.
The exact overlap, fastening pattern, and treatment at eaves, valleys, ridges, and penetrations depend on the product and the roof system. Fasteners should be the type and length specified by the manufacturer and code. Wrinkles, gaps, loose edges, and exposed fastener locations can undermine the underlayment’s performance.
Many products have printed lines to help installers keep courses straight and maintain consistent overlaps. Those lines are guides, not a replacement for written instructions. Windy conditions can make rolls difficult to control, and wet or icy roof surfaces create a serious fall hazard. Roof work should follow appropriate fall-protection practices and local safety requirements.
For self-adhered products, substrate preparation and temperature conditions are particularly important. Some require a primer or a specific deck surface, and the adhesive may not bond properly if the surface is dusty, wet, or too cold. Installation should follow the product data sheet precisely.
Building Codes and Manufacturer Instructions
Roof underlayment requirements in the United States can vary by jurisdiction, roof covering, slope, and local amendments. The International Residential Code (IRC) includes provisions for underlayment beneath roof coverings, but local authorities determine which code edition and amendments apply. Requirements may include specific materials, laps, fastening, or additional protection in certain locations.
In colder regions, code provisions may call for an ice barrier at eaves or other locations where ice dams can cause water backup. An ice barrier is typically a separate, specialized membrane; standard felt should not be assumed to meet that requirement. Local climate, roof geometry, and code rules all affect the details.
Before buying a roll, check with the local building department and review the roofing manufacturer’s installation instructions. Following the more restrictive applicable requirement may be necessary for a compliant, warrantable installation. A product’s marketing description alone does not establish code compliance.
Felt Paper Compared With Synthetic Underlayment
Traditional asphalt felt and synthetic underlayment serve a similar broad purpose, but they are not identical. Felt is familiar and commonly available. Synthetic products are often lighter to carry for the same coverage and may resist tearing or wrinkling differently. Their surface traction, exposure rating, fastening requirements, and compatibility vary by brand.
Neither category is automatically the best choice for every roof. A synthetic product may be unsuitable if a roof-covering manufacturer requires a particular type of felt, and felt may not meet the requirements of a specialized roofing system. Cost should be compared on a coverage basis, including waste and installation needs, rather than by roll price alone.
Some projects use more than one underlayment type—for example, a specialized self-adhered membrane in selected areas and a different underlayment elsewhere. Such combinations should be specified for the roof system and installed according to the manufacturers’ instructions.
Storage and Handling
Keep felt paper rolls dry, protected from direct weather, and stored according to the manufacturer’s directions. Rolls may deform if stored improperly, and wet material can be difficult to install and may not perform as intended. Handling recommendations vary, so labels should be checked for stacking, temperature, and storage limits.
On the roof, rolls should be secured against wind and kept away from edges. Roofers should avoid leaving material exposed beyond its stated limit. If underlayment becomes torn, wrinkled, saturated, or otherwise damaged, it should be evaluated and repaired or replaced according to the product instructions before the roof covering is installed.
Common Buying Mistakes
- Choosing by “15-pound” or “30-pound” alone: Compare the actual product specifications, coverage, and intended use.
- Ignoring roof-covering instructions: The shingle, tile, or metal manufacturer may specify compatible underlayment.
- Underestimating overlap and waste: A roll’s advertised coverage is usually greater than its installed coverage.
- Using felt where an ice barrier is required: These products have different roles and may not be interchangeable.
- Assuming the felt is a finished roof: Roofing felt is underlayment, not a durable exposed roofing surface.
- Leaving the material exposed too long: Weather and ultraviolet exposure can damage products beyond their rated limits.
Frequently Asked Questions
Is roofing felt waterproof?
Roofing felt is water-resistant under the conditions for which it is designed, but it is not a complete waterproof roof. It must be installed with correct laps and details and covered by the specified roofing material. The product’s technical data sheet explains its limitations.
Can roofing felt be left exposed?
It may be exposed temporarily during construction if the product allows it, but exposure time is limited and varies. It should not be treated as a permanent roof covering. Wind, rain, sun, and traffic can damage it.
Can felt paper be used under flooring?
Some papers sold as felt or underlayment are intended for flooring, but roofing felt is not automatically suitable beneath every floor. Flooring manufacturers specify acceptable underlayments, moisture barriers, and installation methods. The product must be selected for the specific assembly.
How can a homeowner choose the right roll?
Identify the roof covering and slope, review manufacturer instructions, confirm local code requirements, and compare product coverage and exposure ratings. For a replacement roof or a complex design, a licensed roofing contractor or local building official can help verify the specification.
Reliable Sources for Project Requirements
For code context, consult the locally adopted International Residential Code and the building department responsible for the property. For product-specific details, use the manufacturer’s current data sheet and installation instructions. The National Roofing Contractors Association (NRCA) also publishes technical guidance for roofing systems and professional practices. These sources are more reliable than assuming every roll of felt has identical performance or installation requirements.