Synthetic vs. Felt Roofing Underlayment: Which Is Right for You?

Introduction

Roof underlayment, often known as roofing paper, is a crucial component in any roofing system. This layer sits between the roof deck and the shingles, providing an extra barrier against elements like rain, wind, and snow. Its primary function is to protect the roof deck from moisture infiltration, which can lead to rot and other structural issues.

There are two main types of roofing underlayment: synthetic roofing underlayment and felt roofing underlayment. Synthetic underlayment is typically made from polypropylene or polyethylene, offering superior durability, tear resistance, and moisture protection. On the other hand, felt underlayment is constructed from organic materials or fiberglass infused with asphalt. While it is more cost-effective, it tends to be heavier and less resistant to tearing and moisture damage.

In this article, we will explore the pros and cons of both synthetic and felt roofing underlayment. This will help you make an informed decision that best suits your needs and priorities for your roofing project.

1. Synthetic Roofing Underlayment

Composition and Manufacturing Process

Synthetic roofing underlayment is made from high-quality polymers such as polypropylene or polyethylene. These materials are designed to perform better than traditional felt underlayment. The manufacturing process involves weaving these polymers into a strong, tear-resistant fabric, often coated with a UV-resistant layer to make it last longer.

Advantages of Choosing Synthetic Roofing Underlayment

1. Durability and Tear Resistance

Synthetic underlayment is incredibly strong and resistant to tearing. This means it will protect your roof for a long time, even in bad weather. Unlike felt, which can easily rip during installation or under strong winds, synthetic underlayment stays intact and performs well over time.

2. Lightweight and Easy Installation

One of the great things about synthetic roofing underlayment is that it’s lightweight. This makes it easier to work with and install, saving time and energy. Roofers love this because it speeds up the installation process and reduces physical strain.

3. Slip Resistance and Moisture Protection

Safety is important when installing a roof, and synthetic underlayment excels in this area with its slip-resistant properties. This makes it safer for roofers working on steep slopes or in wet conditions. Additionally, synthetic underlayment does an excellent job of keeping moisture out, preventing water damage to the roof structure.

Other Advantages

  • UV Stability: Synthetic underlayment doesn’t break down when exposed to sunlight for long periods, so it stays effective even if it’s not covered right away.
  • Longevity: Synthetic options typically last longer than traditional felt underlayment, providing more value over time.
  • Mold Resistance: The materials used in synthetic underlayment naturally resist mold growth, which is better for your roof’s health.

These advantages make synthetic roofing underlayment a top choice for homeowners and professionals who want strong, reliable roofing options.

2. Felt Roofing Underlayment

Felt roofing underlayment, also known as tar paper or asphalt-saturated felt, has been widely used in the roofing industry for many years. It is made from organic or fiberglass fibers saturated with asphalt, which gives it some resistance to water. Felt underlayment serves as a secondary barrier against elements like rain and snow, providing extra protection between your roof deck and the shingles.

Advantages of Choosing Felt Roofing Underlayment

Cost-effectiveness

One of the main advantages of felt roofing underlayment is its affordability. Compared to synthetic options, felt underlayment is usually more budget-friendly. This makes it appealing to homeowners who want to save money without compromising too much on quality.

Limitations and Vulnerabilities

Susceptibility to Tearing and Moisture Damage

While felt roofing underlayment does offer some protection, it also has its limitations:

  • Tearing in Strong Winds: Felt underlayment can tear more easily when exposed to high winds. This makes it less reliable in areas prone to storms.
  • Moisture Penetration: Although felt can resist water to some extent, it is not completely waterproof. If the shingles above are not installed correctly or get damaged, moisture can seep through the felt underlayment, potentially causing rot and other structural problems.

Understanding these strengths and weaknesses can help you decide if felt roofing underlayment is suitable for your specific needs and situation.

Factors to Consider in Your Decision

Choosing between synthetic and felt roofing underlayment involves considering several key factors to ensure the best performance and longevity for your roof. Below are the primary considerations:

1. Geographical Location

The climate and weather conditions of your area significantly impact the performance of different underlayment materials.

  • Hot Climates: In areas with high temperatures, synthetic underlayment offers superior heat resistance and UV stability, preventing it from degrading quickly.
  • Cold Climates: Synthetic underlayment also performs well in cold conditions due to its flexibility, which prevents cracking. Felt can become brittle in freezing temperatures.
  • High Wind Areas: Synthetic underlayment provides better tear resistance, making it more suitable for regions prone to strong winds compared to felt, which can tear easily.

2. Roof Design and Slope

Certain roof styles may require specific underlayment to match their unique characteristics.

  • Steep Slopes: For steeply sloped roofs, synthetic underlayment is often preferred due to its lightweight nature and ease of installation.
  • Low Slopes: On low-sloped roofs, where water drainage is slower, the moisture-resistant properties of synthetic underlayment provide better protection against water infiltration.
  • Complex Designs: Roofs with intricate designs or numerous valleys benefit from the flexibility and durability of synthetic materials, which conform better to odd shapes.

3. Types of Roofing Materials

The compatibility of underlayment with your chosen roofing materials is crucial for optimal performance.

  • Asphalt Shingles: Both synthetic and felt underlayments are commonly used with asphalt shingles. However, synthetic offers longer-lasting protection.
  • Metal Panels: Synthetic underlayment is generally recommended for metal roofs due to its superior moisture resistance and ability to handle temperature fluctuations without deteriorating.
  • Tile Roofs: The heavy weight of tile roofs calls for a durable underlayment like synthetic that can withstand the added stress without tearing.

4. Budgetary Constraints

Balancing cost considerations with the long-term benefits of quality underlayment is essential.

  • Initial Cost: Felt underlayment is more affordable upfront, making it an attractive option for budget-conscious projects.
  • Long-Term Investment: Although synthetic underlayment has a higher initial cost, its durability, longevity, and reduced maintenance needs can result in lower overall costs over time.
  • Project Scope: For large-scale projects or roofs requiring extensive coverage, the lightweight nature of synthetic underlayment can reduce labor costs and installation time.

Understanding these factors will guide you in selecting the most appropriate roofing underlayment for your specific needs. Consider both immediate requirements and future implications when making your decision.

Making the Right Choice for Your Roof

Choosing between synthetic vs felt roofing underlayment depends on what you’re looking for:

Synthetic Underlayment: Durable and Easy to Install

If you prioritize durability and ease of installation, synthetic underlayment is a great choice. Here’s why:

  • Tear-resistant and lightweight, making it easy to handle
  • Provides long-lasting protection for your roof
  • Slip-resistant, reducing the risk of accidents during installation
  • Repels moisture, preventing water damage

These qualities make synthetic underlayment ideal for different climates.

Felt Underlayment: Affordable but Less Resilient

On the other hand, if cost-effectiveness is your main concern, felt underlayment might be suitable. Here’s what you need to know:

  • It’s more prone to tearing and moisture damage compared to synthetic underlayment
  • However, it’s a budget-friendly option that can work well with proper installation techniques
  • Felt underlayment is commonly used in traditional roofing systems

When deciding which type of underlayment to choose, consider these factors:

  1. Geographical Location: Match the underlayment’s properties with your local weather conditions.
  2. Roof Design and Slope: Ensure compatibility with your roof’s structure.
  3. Types of Roofing Materials: Choose an underlayment that complements your chosen roofing materials.
  4. Budgetary Constraints: Balance upfront costs with potential long-term benefits.

By evaluating these aspects, you’ll be able to make an informed decision that suits your specific roofing needs.


Additionally, it’s important to consider the installation process and whether you plan to hire professionals or tackle the installation yourself. Some underlayment options may require special tools or expertise, which could impact your decision. Lastly, don’t forget to check local building codes and regulations to ensure compliance with any specific requirements for underlayment materials. Taking all these factors into account will help you select the most suitable underlayment for your roofing project.


In addition to these considerations, you should also think about the specific climate and weather conditions in your area. If you live in a region with frequent rain or snowfall, you’ll want to choose an underlayment that offers excellent waterproofing properties. Similarly, if you experience high winds or extreme temperatures, opting for a more durable and weather-resistant material would be wise. By tailoring your underlayment choice to your local climate, you can enhance the longevity and performance of your roofing system.

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