What is Synthetic Felt for Roofing? A Comprehensive Guide

Are you considering a new roof or a roof repair project? If so, you’ve probably come across the term “synthetic felt for roofing.” But what exactly is it, and why is it important? In this comprehensive guide, we’ll delve into the world of synthetic felt for roofing, exploring its composition, benefits, and applications in various roofing systems.

First things first, let’s define what synthetic felt for roofing is. It’s a lightweight, non-woven material that serves as an underlayment or base layer in various roofing applications. Unlike traditional organic felt, which is made from wood pulp or cellulose fibers, synthetic felt is manufactured from synthetic materials like polypropylene, fiberglass, or polyester.

Introduction to Synthetic Roofing Felt

Synthetic roofing felt, also known as underlayment, is a crucial component in many roofing systems. It acts as a protective barrier between the roof deck and the primary roofing material, such as asphalt shingles or metal panels. Its primary function is to provide an additional layer of moisture protection, preventing water infiltration and reducing the risk of leaks and damage to the underlying structure.

The Role of Synthetic Felt in Roofing Systems

Underlayment for Asphalt Shingles

One of the most common applications of synthetic felt is as an underlayment for asphalt shingle roofs. In this scenario, the felt is installed directly over the roof deck, creating a smooth and uniform surface for the shingles to be laid upon. It helps prevent wind-driven rain and moisture from penetrating the roof system, extending the lifespan of the shingles and protecting the underlying structure.

Base Layer for Flat Roofs

In flat or low-slope roofing systems, synthetic felt can serve as a base layer or substrate for various roofing materials, such as modified bitumen, built-up roofing (BUR), or single-ply membranes. The felt provides a stable and consistent surface for the roofing materials to adhere to, enhancing the overall performance and durability of the roof system.

Moisture and Vapor Barrier

Synthetic felt can also act as a moisture and vapor barrier, preventing the buildup of condensation within the roof assembly. This is particularly important in regions with high humidity or in buildings with significant indoor moisture sources, as it helps protect against potential mold growth and structural damage.

Composition and Types of Synthetic Roofing Felt

Synthetic roofing felt is available in various types, each with its own unique characteristics and benefits. The most common types include:

Polypropylene Felt

Polypropylene felt is one of the most widely used synthetic roofing felts. It is lightweight, durable, and resistant to moisture, chemicals, and UV radiation. Polypropylene felt is often used as an underlayment for asphalt shingle roofs and can also be used in low-slope roofing applications.

Fiberglass-Reinforced Felt

Fiberglass-reinforced felt is another popular option for roofing underlayment. It combines the strength and durability of fiberglass with the moisture resistance of synthetic materials. This type of felt is particularly suitable for high-temperature applications and is commonly used in regions with extreme weather conditions.

Other Types (e.g., polyester, polyethylene)

While polypropylene and fiberglass-reinforced felts are the most common, other synthetic materials like polyester and polyethylene are also used in the manufacture of roofing felt. These materials offer varying levels of durability, moisture resistance, and fire resistance, allowing for customization based on specific project requirements.

Benefits of Using Synthetic Felt for Roofing

Synthetic felt offers numerous advantages over traditional organic felt, making it a popular choice among roofing professionals and homeowners alike. Here are some of the key benefits:

Durability and Longevity

One of the primary advantages of synthetic felt is its exceptional durability and longevity. Unlike organic felt, which can deteriorate over time due to moisture exposure and biological degradation, synthetic felt is resistant to these elements. With proper installation and maintenance, synthetic felt can last for decades, providing long-term protection for your roof.

Weather Resistance

Synthetic roofing felt is designed to withstand harsh weather conditions, including heavy rain, wind, and extreme temperatures. Its moisture-resistant properties prevent water penetration, while its UV resistance ensures that it won’t degrade or become brittle under prolonged exposure to sunlight.

Ease of Installation

Synthetic felt is generally lighter and more flexible than traditional organic felt, making it easier to handle and install. Its non-woven structure allows for better conformation to the contours of the roof deck, reducing the risk of wrinkles or gaps that could compromise the roofing system’s integrity.


While the initial cost of synthetic felt may be higher than organic felt, its extended lifespan and lower maintenance requirements can result in significant cost savings over time. Additionally, the improved performance and protection offered by synthetic felt can help prevent costly repairs or premature roof replacements.

Installation Process of Synthetic Felt

The installation process for synthetic felt is similar to that of traditional organic felt, but there are a few key considerations to ensure optimal performance and longevity. Here’s a general overview:

Preparing the Roof Deck

Before installing the synthetic felt, it’s crucial to ensure that the roof deck is clean, dry, and free from any debris or irregularities. Any damaged or rotted areas should be repaired or replaced to provide a solid and stable base for the felt and subsequent roofing materials.

Laying the Felt

The synthetic felt is typically rolled out horizontally, starting at the eaves and working upwards towards the ridge. Adjacent courses should overlap according to the manufacturer’s recommendations, typically by a minimum of 4 inches (10 cm) to ensure proper water shedding.

Overlapping and Fastening

In addition to overlapping the felt courses, it’s important to properly fasten the felt to the roof deck using cap nails or staples. This helps prevent wind uplift and ensures a secure and durable installation. The fastening pattern and spacing should follow the manufacturer’s guidelines or local building codes.

Comparison with Traditional Organic Felt

While synthetic felt offers numerous advantages, it’s important to understand how it compares to traditional organic felt, which has been a staple in the roofing industry for decades. Here’s a closer look at the key differences:

Performance Differences

Synthetic felt out performs organic felt in several ways. It has superior moisture resistance, durability, and resistance to biological degradation. Synthetic felt also offers better UV stability and can withstand extreme temperatures without becoming brittle or deteriorating. Additionally, it is generally lighter and easier to work with during installation.

Environmental Impact

From an environmental standpoint, synthetic felt has a lower carbon footprint compared to organic felt, as it is manufactured from synthetic materials rather than natural resources like wood pulp. However, organic felt is biodegradable and potentially more eco-friendly at the end of its lifespan.

Cost Considerations

The initial cost of synthetic felt is typically higher than organic felt. However, its extended lifespan and lower maintenance requirements can offset the higher upfront cost over time. Furthermore, the improved performance of synthetic felt can lead to cost savings by preventing premature roof failures and reducing the need for frequent replacements.

Maintenance and Care for Synthetic Felt Roofs

Like any roofing component, synthetic felt requires proper maintenance and care to ensure its longevity and optimal performance. Here are some essential maintenance practices:

Regular Inspections

It’s crucial to conduct regular inspections of the synthetic felt roof, at least twice a year (spring and fall) or after severe weather events. Look for any signs of damage, such as punctures, tears, or loose seams, and address them promptly.

Repairing Damage

If any damage to the synthetic felt is discovered during inspections, it should be repaired promptly using compatible sealants and repair materials specifically designed for the type of felt used. Proper repair techniques are crucial to prevent further damage and maintain the integrity of the roofing system.

Replacing Aged Felt

While synthetic felt has an extended lifespan, it may eventually need to be replaced, especially if it has been subjected to severe weathering or mechanical damage over time. Consult with a professional roofing contractor to determine when replacement is necessary and to ensure proper installation of the new felt.

Factors to Consider When Choosing Synthetic Felt

When selecting the appropriate synthetic felt for your roofing project, there are several factors to consider to ensure optimal performance and compliance with local building codes and regulations:

Climate and Weather Conditions

Different types of synthetic felt may be better suited for certain climate and weather conditions. For example, fiberglass-reinforced felt may be preferable in regions with extreme temperatures or high wind loads, while polypropylene felt may be more suitable for milder climates.

Roof Slope and Design

The slope and design of the roof can also influence the choice of synthetic felt. Steep-slope roofs may require different underlayment materials or installation techniques compared to low-slope or flat roofs.

Building Codes and Requirements

It’s essential to consult local building codes and regulations to ensure that the selected synthetic felt meets the required specifications for your area. Some regions may have specific requirements for fire resistance, wind uplift resistance, or other performance criteria.

Compatibility with Other Roofing Materials

Synthetic felt is compatible with a wide range of roofing materials, but it’s important to consider potential interactions and ensure proper installation techniques:

Asphalt Shingles

Synthetic felt is commonly used as an underlayment for asphalt shingle roofs. It provides a smooth and consistent surface for the shingles to be installed, while also offering moisture protection and preventing wind-driven rain from penetrating the roof system.

Metal Roofing

When used with metal roofing systems, synthetic felt can serve as a barrier between the metal panels and the roof deck, protecting against moisture and condensation buildup. It can also help reduce noise and vibration from the metal panels.

Tile Roofing

For tile roofing applications, synthetic felt can act as an underlayment or base layer, providing a stable surface for the tiles to be installed upon. It can also help prevent moisture intrusion and protect the roof deck from potential damage.

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Synthetic felt for roofing has become an essential component in modern roofing systems, offering superior performance, durability, and protection compared to traditional organic felt. With its moisture resistance, weather resilience, and ease of installation, synthetic felt is a valuable investment for both residential and commercial roofing projects.

When it comes to choosing the right synthetic felt for your roofing needs, it’s crucial to consider factors such as climate, roof slope, and local building codes. By working with a reputable roofing contractor and following proper installation guidelines, you can ensure that your synthetic felt roof provides long-lasting protection and peace of mind for years to come.


  1. How long does synthetic felt for roofing typically last? The lifespan of synthetic felt for roofing can vary depending on the type and quality of the material, as well as the environmental conditions and maintenance practices. Generally, high-quality synthetic felt can last between 20 to 30 years or more with proper installation and care.
  2. Is synthetic felt more expensive than traditional organic felt? Yes, synthetic felt typically has a higher initial cost compared to organic felt. However, the longer lifespan, lower maintenance requirements, and improved performance of synthetic felt can offset the higher upfront cost over time.
  3. Can synthetic felt be used on any type of roof? Synthetic felt is suitable for various roofing systems, including asphalt shingle roofs, flat or low-slope roofs, and metal roofing applications. However, it’s essential to consult with a professional roofing contractor to ensure that the chosen synthetic felt is compatible with your specific roof type and design.
  4. How is synthetic felt installed? Synthetic felt is typically installed in horizontal courses, starting from the eaves and working upwards towards the ridge. Adjacent courses are overlapped according to the manufacturer’s recommendations, and the felt is secured to the roof deck using cap nails or staples to prevent wind uplift.
  5. Can synthetic felt be recycled or reused? Yes, many types of synthetic felt, such as those made from polypropylene or polyester, can be recycled and reused, contributing to sustainable building practices and reducing waste in the construction industry.
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Spike Miller

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