Roof felt, a crucial roofing underlayment, protects against moisture and extends roof lifespans. Homeowners often face a choice: 15-pound (15#) vs 30-pound (30#) roof felt paper. This guide explores both types, covers installation contexts, lifespan, and value, and helps American homeowners make informed decisions.

Feature	15 Roof Felt	30 Roof Felt
Thickness	Thinner (about half as thick)	Thicker (more durable)
Weight/Square	~15 lbs	~30 lbs
Best For	Steep roof pitches	Low-slope, longer exposure
Lifespan (exposed)	Short-term (days to a week)	Longer (weeks if needed)
Cost	Lower	Higher
Common Use	Standard shingle jobs	High-end, tile, or challenging roofs

What Is Roof Felt Paper?

Roof felt paper, also called roofing underlayment or tar paper, is a flexible sheet made of a base (often fiberglass or organic material) saturated with asphalt. Installed between roof decking and final roof shingles, felt serves as a protective moisture barrier. It helps prevent water damage, retains shingle alignment, and offers a backup layer if shingles are compromised.

How Are Roofing Felt Papers Classified?

Roofing felt is primarily designated by weight—15-pound (15#) and 30-pound (30#). The pound measurement refers to the weight of one square (100 sq. ft.) before full saturation. Modern felts usually weigh less due to manufacturing advancements, but the labels help distinguish relative thickness and durability.

• 15
  

  Roofing Felt: Thinner, lighter, more economical.

• 30
  

  Roofing Felt: Thicker, heavier, stronger, offers more protection.

Key Differences Between 15

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and 30# Roof Felt Paper

Material Thickness And Durability

30

felt paper is approximately twice as thick as 15# felt. This increase in thickness means 30# felt is less susceptible to tearing during installation or when exposed to foot traffic. Durability is one of the most important differentiators between these two types.

Protection From Moisture And Weather Exposure

Because of its thickness, 30

felt offers better resistance against moisture and wind-driven rain. It performs better during heavy storms or when the roof decking is exposed before shingles are laid, making it a wise choice in climates with high precipitation or wind.

Application Differences

• 15
  

  felt is commonly used on steeper-sloped roofs where water will drain quickly and less exposure to standing water is expected.

• 30
  

  felt is preferred for low-sloped roofs and areas prone to ice dams or standing water, as it provides more robust secondary protection.

Cost Considerations

15

felt is generally less expensive than 30# felt due to its thinner composition. If budget constraints are significant and environmental factors do not dictate thicker felt, 15# is a practical solution. However, the added protection of 30# felt may justify its higher cost in many scenarios.

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When To Use 15

Roof Felt Paper

15

roofing felt excels on homes where:

• Roof pitch is steep (4:12 or higher), minimizing water pooling risks.
• Shingles or tiles will be installed quickly, limiting underlayment exposure to weather.
• Budget constraints require lower material costs without significantly sacrificing protection.

Most standard residential asphalt shingle installations in moderate climates use 15

roofing felt as their underlayment of choice.

When To Use 30

Roof Felt Paper

30

felt paper shines in situations where:

• The roof slope is shallow (between 2:12 and 4:12), risking slower water runoff.
• Longer delays may occur before shingles are installed (due to weather or project phasing).
• The roof is at a higher risk of leaks—for example, on older homes or those with intricate rooflines.
• High-end roofing materials (tile, slate, wood shakes) are utilized, requiring more robust support.

This makes 30

felt a preferred option for extra durability and peace of mind.

Building Code Requirements And Industry Best Practices

Local building codes and International Residential Code (IRC) guidelines establish minimum underlayment standards. Most American jurisdictions require at least one layer of 15

felt for steep-slope roofs, but some regions (especially with low slopes or severe climates) require 30# felt or synthetic alternatives.

• Always check local building code requirements before selecting roofing felt.
• Some manufacturers’ warranties may specify or require 30
  

  felt for certain roof types.

Installation Steps For 15

And 30# Roof Felt

Tools And Supplies Needed

• Roof felt rolls (15
  

  or 30# as needed)

• Utility knife or scissors
• Stapler, cap nails, or felt tacks
• Roofing hammer
• Tape measure/chalk line

Step-By-Step Installation Overview

1. Clean the roof decking of debris and ensure it is completely dry.
2. Start at the eaves, rolling out the felt horizontally and overlapping each course by at least 2-4 inches.
3. Fasten the felt every 12-24 inches, ensuring no sagging or tears. Use cap nails or staples for strong wind-prone regions.
4. At roof valleys and ridges, increase overlap for additional protection.
5. Cover all deck areas before installing shingles, tiles, or other finish roofing.

30

felt is heavier and may require an extra helper to manage large rolls safely.

Comparing Advantages And Disadvantages

Aspect	15 Roof Felt	30 Roof Felt
Handling/Ease Of Installation	Lighter, easier for one person to handle, less fatigue	Heavier, more challenging to manipulate alone
Resilience To Foot Traffic	More prone to tearing during installation	Resistant to tearing and heavy traffic
Performance In Extreme Weather	Adequate for most moderate climates	Superior, especially in storm-prone/icy areas
Cost Efficiency	Lower material and shipping cost	Higher upfront expense
Life Expectancy (Exposed)	1 week or less	2-3 weeks or longer

Roofing Felt Vs. Synthetic Underlayment

Many homeowners now ask: Should I use traditional felt or synthetic underlayment? Synthetics (e.g., polypropylene-based) offer lighter weight, higher tear resistance, and longer UV exposure tolerance. However, felt paper remains a popular, cost-effective choice, especially for traditional shingle jobs.

• Synthetics last longer exposed, but cost more.
• 15
  

  and 30# felt are time-tested and compatible with most shingle manufacturing warranties.

How Roof Felt Paper Protects Your Investment

Well-chosen felt paper ensures:

• Deck Protection: Shields wood decking from water intrusion and rot.
• Shingle Alignment: Smoothes out surface irregularities beneath shingles.
• Condensation Mitigation: Reduces moisture buildup from attic vapor migration.
• Fire Resistance: Provides a limited but valuable layer of fire retardance.

Cost Comparison: 15

Vs. 30# Felt Paper

Material	Approximate Cost per Roll (432 sq. ft.)	Coverage/Bundle
15 Felt	$20 – $30	432 sq. ft. (1 roll)
30 Felt	$35 – $50	216 sq. ft. (1 roll)

While 30

felt rolls cover about half as much area per roll, the incrementally higher cost pays off in durability and peace of mind for critical applications.

Common Questions About 15

vs 30# Roof Felt Paper

Can You Mix 15

And 30# Felt?

Blending both is not recommended for the same roof face. Doing so complicates warranty claims and performance predictability. Stick to one type per roof section for optimal results.

How Long Can Felt Paper Remain Exposed?

15

felt should remain exposed no more than 1 week; 30# felt can last 2-3 weeks, depending on weather. Prolonged exposure increases tearing and reduces water resistance.

Is Roof Felt Required Under All Roofing Materials?

Nearly all shingle and tile manufacturers, as well as building codes in most U.S. jurisdictions, require some form of underlayment—either felt or synthetic—for residential roofs.

Comparing Roof Felt Brands And Quality Considerations

Not all felt paper is created equal; several national brands offer varying qualities:

• GAF and CertainTeed: Industry leaders with well-tested felt.
• Atlas Roofing and Owens Corning: Robust offerings for both 15
  

  and 30# paper.

Look for UL-listed and ASTM D4869 compliance for roofing felt products used in the U.S.

Climate And Regional Impact On Choice Between 15

And 30#

In warm, dry regions (like the Southwest), 15

felt is often sufficient for steep roofs. In cold, wet, or coastal areas, 30# felt provides added resilience against ice dams and blowing rain.

Always consider local rainfall, snow loads, and wind codes when choosing an underlayment weight.

Professional Recommendations For Homeowners

• For standard asphalt shingle re-roof jobs on steep-pitched roofs, 15
  

  is generally adequate.

• Consider 30
  

  felt if your roof has a complex design, low pitch, or is in a region with severe weather.

• If uncertain, ask your roofing contractor for their experience-based guidance and check manufacturer specs for your specific shingle model.

Maintenance And Lifespan Considerations

Both types are designed to serve as temporary water barriers during installation, then as secondary protection during the roof’s service life. Routine attic inspections for leaks or condensation can reveal if the underlayment is compromised.

Environmental Impact Of Roofing Felt Paper

Both 15

and 30# felt papers contain asphalt, a petroleum product, and are not biodegradable. Proper disposal practices should be observed at the job’s end. Innovations in recycling and eco-friendly synthetic underlayments are growing, but felt remains a standard in the U.S. market due to cost and tradition.

Roof Felt Paper 15 Vs. 30: Quick-Reference Decision Table

Scenario	Recommended Felt
Steep slope, asphalt shingles, dry climate	15#
Low slope, possible ice dams, significant delays	30#
High-value roof, slate/tile installation	30#
Budget-conscious, standard replacement, quick install	15#

Final Thoughts On Roof Felt Paper 15 Vs. 30 For American Homeowners

Choosing between 15

and 30# roof felt paper is about balancing budget, climate, roof pitch, and risk tolerance. While both options are tried and true, selecting the appropriate weight optimizes your roof’s performance and lifespan. Consult your local building codes and trusted professionals for tailored advice.

How to Get the Best Roofing Quotes

• Prioritize Workmanship
  A roof is one of your home’s most important investments. Always choose a contractor based on experience and reputation — not just price. Poor installation can lead to expensive problems down the road.
• Compare Multiple Estimates
  Don’t settle for the first quote you receive. It’s always a smart move to compare at least three bids from local roofing professionals. You can 877-801-4315 to get local quotes from roofing contractors in your area, available across the United States.
• Use Negotiation Tactics
  After selecting a trusted roofer, be sure to use our proven tips — How to Negotiate with Roofing Contractors — to secure the best possible final price without cutting corners.