Is Synthetic Roofing Underlayment Better Than Felt?

When it comes to roofing projects, the underlayment plays a crucial role in protecting your home or building from water damage and ensuring the longevity of your roof. Traditionally, felt underlayment has been the go-to choice for many years. However, with advancements in technology, synthetic roofing underlayment has emerged as a popular alternative, offering several advantages over its felt counterpart.

Definition of roofing underlayment

A roofing underlayment is a protective layer installed directly on the roof deck before the primary roofing material, such as shingles or tiles. Its primary function is to act as a moisture barrier, preventing water from seeping through the roof deck and causing damage to the structure.

Traditional felt underlayment

Felt underlayment, also known as tar paper or asphalt-saturated felt, has been a staple in the roofing industry for decades. It is made from a base of organic materials, such as wood cellulose fibers or recycled paper products, that are saturated with asphalt or tar for waterproofing.

Synthetic roofing underlayment

Synthetic roofing underlayment is a modern alternative to traditional felt underlayment. It is typically made from synthetic materials, such as polypropylene or polyethylene, which are engineered to provide superior performance and durability compared to felt underlayment.

Advantages of Synthetic Roofing Underlayment

Synthetic roofing underlayment offers several advantages over traditional felt underlayment, making it a compelling choice for homeowners and contractors alike.

Durability and longevity

One of the primary advantages of synthetic roofing underlayment is its exceptional durability and longevity. Unlike felt underlayment, which can deteriorate over time due to exposure to moisture and UV radiation, synthetic underlayment is designed to withstand these environmental factors. It can last for decades without losing its structural integrity or performance.

Moisture resistance

Synthetic underlayment is highly resistant to moisture, which is crucial for preventing water damage and ensuring the long-term protection of your roof. Unlike felt underlayment, which can absorb and retain moisture, synthetic underlayment effectively repels water, preventing it from seeping through to the roof deck.

Slip resistance

Many synthetic underlayment products feature a textured or slip-resistant surface, providing enhanced traction for roofers during installation. This added safety feature can be particularly beneficial when working on steep or sloped roofs, reducing the risk of accidents and injuries.

Ease of installation

Synthetic underlayment is generally lighter and more flexible than felt underlayment, making it easier to handle and install. This can lead to faster installation times and reduced labor costs, which can be advantageous for both homeowners and contractors.

Environmental impact

Synthetic roofing underlayment is often made from recycled materials, such as post-consumer plastic, making it a more environmentally friendly option compared to traditional felt underlayment, which can contribute to deforestation and landfill waste.

Disadvantages of Felt Underlayment

While felt underlayment has been a longstanding choice in the roofing industry, it has several limitations that make synthetic underlayment a more appealing option.

Limited lifespan

Felt underlayment has a relatively short lifespan compared to synthetic underlayment. Exposure to moisture, UV radiation, and temperature fluctuations can cause felt to deteriorate over time, potentially compromising its effectiveness as a moisture barrier.

Moisture absorption

Felt underlayment is prone to absorbing and retaining moisture, which can lead to issues such as mold growth, rot, and structural damage. This moisture absorption can also make felt underlayment heavier and more difficult to work with during installation.

Wrinkles and tears

Felt underlayment is susceptible to wrinkling and tearing, especially during installation or when exposed to high winds. These imperfections can create gaps and weaknesses in the moisture barrier, increasing the risk of water infiltration and potential damage to the roof deck.

Environmental concerns

The production of felt underlayment can contribute to deforestation and the depletion of natural resources. Additionally, the asphalt or tar used in felt underlayment can be harmful to the environment if not disposed of properly.

Types of Synthetic Roofing Underlayment

Synthetic roofing underlayment comes in various forms, each with its own unique properties and advantages.

Non-woven synthetic underlayment

Non-woven synthetic underlayment is made from a dense mat of randomly oriented fibers that are bonded together. This type of underlayment is highly durable, breathable, and resistant to moisture and UV radiation. It is often used in residential and commercial roofing applications.

Woven synthetic underlayment

Woven synthetic underlayment is made from interlaced synthetic fibers, creating a strong and durable material. It is highly tear-resistant and can be an excellent choice for steep-slope roofing applications or areas prone to high winds.

Rubberized asphalt synthetic underlayment

Rubberized asphalt synthetic underlayment combines the benefits of traditional asphalt underlayment with the durability and moisture resistance of synthetic materials. This type of underlayment is often used in high-temperature climates or in areas with extreme weather conditions.

Installation Considerations

When choosing between synthetic roofing underlayment and felt underlayment, several factors should be taken into consideration to ensure optimal performance and compliance with local building codes and regulations.

Roof slope and climate

The slope of your roof and the climate in your area can play a significant role in determining the most suitable underlayment material. For example, in regions with high humidity or frequent rainfall, a highly moisture-resistant synthetic underlayment may be the better choice.

Compatibility with roofing materials

It’s essential to ensure that the underlayment material you choose is compatible with the primary roofing material, such as asphalt shingles, metal, or tile. Some underlayment products may be better suited for specific roofing types, so consulting with a professional roofer or manufacturer is recommended.

Local building codes and regulations

Different regions and municipalities may have varying building codes and regulations regarding the use of roofing underlayment materials. It’s crucial to research and comply with these regulations to ensure your roofing project meets local standards and requirements.

Cost Comparison

While synthetic roofing underlayment typically has a higher initial material cost compared to felt underlayment, it’s important to consider the long-term cost implications and potential savings.

Initial material costs

The upfront cost of synthetic roofing underlayment is generally higher than that of felt underlayment. However, it’s important to consider the long-term benefits and potential cost savings that synthetic underlayment can provide.

Installation costs

In some cases, the installation costs for synthetic underlayment may be lower than those for felt underlayment. This is because synthetic underlayment is often lighter, more flexible, and easier to handle, which can lead to faster installation times and reduced labor costs.

Long-term savings

While the initial investment in synthetic roofing underlayment may be higher, its superior durability and longevity can result in significant long-term cost savings. By avoiding the need for frequent replacements and minimizing the risk of water damage and associated repairs, synthetic underlayment can potentially save homeowners and building owners money over the life of their roof.

Maintenance and Repair

Proper maintenance and timely repairs are essential for ensuring the performance and longevity of any roofing system, regardless of the underlayment material used.

Inspecting and replacing damaged underlayment

Regular inspections of your roof and underlayment are recommended to identify any areas that may have become damaged or compromised. If you notice any tears, punctures, or signs of deterioration in the underlayment, it’s important to address these issues promptly by replacing the affected sections.

Protecting the underlayment during roof repairs

During roof repairs or replacements, it’s crucial to take precautions to protect the existing underlayment from further damage. This may involve temporarily covering exposed areas or using protective barriers to prevent punctures or tears.

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In the debate between synthetic roofing underlayment and traditional felt underlayment, it’s clear that synthetic options offer several advantages in terms of durability, moisture resistance, ease of installation, and environmental impact. While the initial material cost may be higher, the long-term benefits and potential cost savings make synthetic underlayment a compelling choice for homeowners and contractors seeking a high-performance, reliable roofing solution.

Ultimately, the decision between synthetic and felt underlayment will depend on factors such as your local climate, roof slope, compatibility with roofing materials, and budget considerations. By carefully weighing the pros and cons of each option and consulting with professionals in the roofing industry, you can make an informed decision that meets your specific needs and ensures the longevity and protection of your roof.


1. Can synthetic roofing underlayment be used with any type of roofing material?

While synthetic underlayment is compatible with most roofing materials, it’s always best to consult with the manufacturer or a professional roofer to ensure compatibility with your specific roofing system.

2. How long does synthetic roofing underlayment typically last?

The lifespan of synthetic underlayment can vary depending on the specific product and environmental conditions, but many high-quality synthetic underlayments are designed to last 20-30 years or more.

3. Is synthetic underlayment more difficult to install than felt underlayment?

No, synthetic underlayment is generally easier to install than felt underlayment. It is lighter, more flexible, and often comes in larger rolls, which can make the installation process faster and more efficient.

4. Can synthetic underlayment be used on low-slope or flat roofs?

Yes, many synthetic underlayment products are suitable for use on low-slope or flat roofs, provided that they meet the manufacturer’s recommendations and local building codes.

5. Is synthetic underlayment more expensive to repair or replace than felt underlayment?

While the initial material cost of synthetic underlayment may be higher, its durability and longevity can potentially result in lower repair and replacement costs over the lifetime of the roof.

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Spike Miller

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