Synthetic underlayment is generally the better choice over felt due to its superior durability, weather resistance, and ease of installation. While both types of underlayment serve the essential function of protecting the roof deck beneath shingles, synthetic materials offer longer-lasting performance, especially in harsh weather conditions and prolonged exposure to UV rays. This makes them the preferred option for most modern roofing projects, despite a higher upfront cost.
In this article, we explore the key differences between synthetic and felt underlayment, including their composition, advantages, and disadvantages. You'll also find a side-by-side comparison chart, guidance on when to choose one over the other, and insights into how climate, budget, and project goals should influence your decision.
Roofing underlayment is a protective layer installed between the roof deck (typically made of plywood or OSB) and the final roofing material, such as shingles or tiles. Its primary function is to act as a secondary barrier against water intrusion, preventing moisture from seeping into the structure in case the outer roofing material becomes damaged or compromised.
Underlayment also provides additional protection during the construction phase, shielding the roof deck from wind, rain, and UV exposure before the final roofing is installed. Available in different materials—most commonly felt and synthetic—roofing underlayment enhances the overall durability and weather resistance of a roof system.
Felt underlayment, also known as tar paper or asphalt-saturated felt, has been a staple in roofing for over a century. It's typically made from recycled paper products or fiberglass mats saturated with asphalt, giving it its characteristic black appearance and water-resistant properties. Felt underlayment comes in different weights, most commonly 15-pound (15#) and 30-pound (30#), with the latter being thicker and more durable.
Felt underlayment, also known as asphalt-saturated felt, has been a trusted roofing material for decades. It remains a popular choice for certain projects due to its affordability and proven performance in many residential applications.
Felt underlayment is generally more affordable than synthetic options, making it a budget-friendly solution for homeowners or contractors looking to reduce material costs. Its low price point is especially appealing for short-term roofing projects or smaller builds.
Due to its long history of use, felt underlayment is widely stocked at most building supply stores. This makes it easy to source locally and quickly when timelines are tight.
When installed correctly, felt underlayment offers reliable protection against moisture infiltration. It serves as an effective secondary barrier, helping to prevent leaks if shingles are damaged or dislodged.
Felt works well with conventional roofing materials like asphalt shingles, and many roofers are familiar with its installation process. This familiarity can lead to fewer mistakes and smoother project execution.
Overall, while it may not offer the advanced performance features of synthetic underlayment, felt remains a viable, dependable option in many standard roofing applications.
While felt underlayment has served as a roofing staple for decades, it comes with several limitations that make it less ideal for modern or demanding applications. Understanding these drawbacks can help homeowners and contractors make a more informed choice.
Felt underlayment is more prone to tearing, especially during installation or under heavy foot traffic. It can also degrade quickly in extreme weather conditions compared to synthetic options.
Felt is heavier and comes in smaller rolls, making it more cumbersome to handle and install. This can lead to increased labor time and physical strain on workers.
Felt deteriorates quickly when exposed to sunlight, often within a few days. This limits the window for installing shingles and can be problematic if project delays occur.
Unlike synthetic materials, felt can absorb moisture, which may cause it to wrinkle or buckle. These deformities can interfere with the proper installation of shingles and reduce overall roof performance.
In conclusion, while felt underlayment is cost-effective and accessible, its limitations in durability, moisture resistance, and exposure tolerance make it less suitable for long-term or high-performance roofing needs.
Synthetic underlayment has burst onto the roofing scene as a superior alternative to felt, addressing many of its shortcomings. These products are typically made from woven or spun-bound polypropylene or polyethylene, often reinforced with polymers, making them incredibly strong, lightweight, and highly water-resistant.
Synthetic underlayment has become the modern standard in roofing due to its advanced materials and performance features. Designed to outperform traditional felt, it offers a range of benefits that make it ideal for both residential and commercial roofing projects.
Synthetic underlayment is highly resistant to tearing, stretching, and punctures, making it ideal for challenging weather conditions and heavy foot traffic during installation. This durability ensures long-lasting protection and fewer chances of failure over time.
Unlike heavy felt rolls, synthetic underlayment is lightweight and comes in larger sheets, which reduces installation time and physical strain. Its ease of handling also helps improve overall job site efficiency.
Synthetic materials repel water rather than absorb it, offering better protection against rain and moisture. Many products also include UV-resistant coatings, allowing them to withstand prolonged sun exposure without degrading.
Many synthetic underlayments are designed with textured or slip-resistant surfaces, providing better traction for installers. This is especially beneficial on steep or high-pitched roofs where safety is critical.
In summary, synthetic underlayment provides exceptional strength, weather protection, and ease of use, making it a top choice for roofing professionals seeking reliability and long-term performance.
While synthetic underlayment offers numerous advantages, it's important to consider its potential drawbacks before making a final decision. These disadvantages, although fewer than with felt, may impact cost, installation, or product selection depending on your specific roofing project.
Synthetic underlayment typically comes with a higher upfront price than felt. For budget-conscious projects, this added cost may be a deciding factor, especially for large-scale installations.
Despite many products being marketed as slip-resistant, synthetic underlayment can still become slick in rainy or humid conditions. This can pose a safety risk for workers during installation, particularly on steep slopes.
Not all synthetic underlayments are created equal—some low-cost versions may lack the strength, UV resistance, or water repellency of premium options. Choosing a poor-quality product can negate many of the expected benefits.
In conclusion, while synthetic underlayment excels in performance and durability, it does come with considerations such as higher cost, potential safety concerns, and the importance of selecting a reputable brand. Proper evaluation can help ensure it’s the right choice for your roofing needs.
Let's summarize the key differences across various critical factors:
| Factor | Synthetic Underlayment | Felt Underlayment |
| Durability | Excellent tear, wind, and puncture resistance | Moderate; can tear easily, especially when wet |
| Weight & Handling | Lightweight; easier to transport and install | Heavier and bulkier; more labor-intensive |
| Water Resistance | Repels water; does not absorb moisture | Absorbs water; can wrinkle or degrade if wet |
| UV Resistance | High (can be exposed for 90–180 days depending on the product) | Low (usually only safe for a few days of exposure) |
| Slip Resistance | Often designed with textured, anti-slip surfaces | Generally smooth; can become slippery when wet |
| Roll Coverage | Larger rolls (up to 10 squares per roll) for faster installation | Smaller rolls (typically 2 squares per roll) |
| Installation Speed | Faster due to wider, lighter rolls and fewer seams | Slower due to smaller rolls and more overlaps |
| Compatibility | Works well with most modern roofing systems | Ideal for traditional asphalt shingle roofs |
| Cost | Higher upfront cost, lower long-term risk | Lower upfront cost, may incur more maintenance or replacement |
| Longevity | Long-lasting; holds up under extreme conditions | Shorter lifespan; degrades faster over time |
| Category | Winner |
| Durability | ✅Synthetic |
| Ease of Install | ✅Synthetic |
| Water Resistance | ✅Synthetic |
| UV Protection | ✅Synthetic |
| Cost | ✅ Felt |
| Availability | ✅ Felt |
| Short-Term Use | ✅ Felt |
| Long-Term Value | ✅Synthetic |
No matter which underlayment you choose—synthetic or felt—certain key considerations apply to ensure the success and longevity of your roofing system. These factors can influence performance, installation quality, and long-term protection for your home.
Even the best underlayment can fail if it's improperly installed. Following manufacturer guidelines and local building codes is essential to ensure the material performs as intended and maintains its warranty.
Try to schedule installation during favorable weather, as both synthetic and felt can be affected by wind, rain, and extreme temperatures. Wet or windy conditions can make installation more dangerous and compromise the integrity of the underlayment.
Steep-slope roofs may benefit more from underlayments with enhanced slip resistance, while low-slope roofs might require additional waterproofing layers. The architectural complexity of your roof can also affect underlayment selection and installation difficulty.
Always choose a reputable brand, regardless of the type of underlayment. Low-quality materials can wear out quickly, cancel out warranty coverage, and lead to premature roof failure.
While selecting the right type of underlayment is important, how it's installed and maintained is equally vital. Prioritizing proper techniques, suitable conditions, and quality products will help you get the most value from your roofing investment.
When it comes to choosing between synthetic and felt underlayment, synthetic is generally the better option thanks to its superior durability, weather resistance, and ease of installation. While felt remains a more affordable and familiar choice for some, it doesn't offer the same long-term performance or protection.
In this article, we compared both types across key factors like cost, moisture resistance, installation, and safety. We also outlined their pros and cons, provided a side-by-side comparison, and highlighted important considerations regardless of which type you choose. With this information, you can make a more informed decision tailored to your roofing needs.
