From Felt to Synthetic: Discovering the Different Types of Roof Underlayment 

Posted on July 22, 2023

From Felt to Synthetic: Discovering the Different Types of Roof Underlayment 

Underlayment is one essential component of your roof that often goes unnoticed. It is a protective layer installed beneath the roofing materials to provide an extra barrier against moisture, weather damage, and other threats. Multiple underlayment materials are available on the market, each with unique properties and advantages. This article will help you explore the various kinds of roof underlayment materials, their installation methods, and potential points of failure.

◾ Types of Roof Underlayment: Exploring Different Materials

Several roof underlayment materials are available, each with unique features and benefits. From traditional asphalt felt to synthetic underlayment and rubberized asphalt, exploring these different materials allows you to make an informed decision and ensure the durability and longevity of your roof. When it comes to choosing the best roof underlayment, it ultimately depends on factors such as your specific roofing needs, the local climate, and your budget.

#1. Asphalt-Saturated Felt

This underlayment provides an extra level of defense, protecting your roof from potential water damage, ice dams, and wind-driven rain. It is available in two thicknesses: #15 and #30. Each type of underlayment has a permanence rating, which is the measure of how much water can transfer through the material. The #15 felt typically has a perm rating of six, while the #30 felt has a rating of five, offering better protection and durability. Asphalt-saturated felt underlayment is water-resistant but not waterproof. It is typically made from organic or fiberglass substrate, with the organic variant being more common.

 Asphalt-Saturated Felt

 Felt Underlayment Installation

  1. Proper Overlap for Leak Prevention: For low-slope roofs (2/12 up to 4/12) ensure a minimum overlap of 19 inches between felt courses, providing a double layer of underlayment across the entire roof. Steep-slope roofs (4/12 and steeper) upper courses of felt underlayment should have a minimum two-inch overlap with lower courses.
  1. Fastening Methods for Enhanced Wind Resistance: Standard fastening uses staples to secure the felt underlayment. In high-wind areas, consider using plastic wind strips or caps to prevent tearing and improve wind resistance.
  1. Eave and Rake Edge Metal Overlap: Proper protection: Ensure the metal drip edge along the eaves and rakes overlap the underlayment for better protection.  

#2. Rubberized Asphalt

Rubberized asphalt is another type of underlayment material that offers excellent sealing properties. Thanks to the adhesive on one side, it is self-adhering, protected by a peel-off membrane. Rubberized asphalt underlayments can be manufactured with additional features, such as non-skid surfaces, polymer films for improved moisture resistance, fiberglass reinforcement, or mineral coatings for enhanced weather resistance.

Rubberized Asphalt Roof Underlayment

 Rubberized Asphalt Underlayment Installation

  1. Preparation: Before the installation, the roof surface needs to be clean, dry, and free from any debris or loose materials. Any existing underlayment or damaged sections may need to be removed or repaired.
  2. Safety measures: It’s essential to take safety precautions, such as wearing appropriate personal protective equipment (PPE), including gloves and safety goggles, to protect yourself during the installation process.
  3. Application: Rubberized asphalt underlayment typically comes in rolls. Start by unrolling the material along the roof’s eaves, ensuring it is appropriately aligned. Secure it using roofing nails or staples, following the manufacturer’s fastener spacing and placement guidelines.
  4. Overlapping: To create a watertight seal, each subsequent row of rubberized asphalt underlayment should overlap the previous row by a specified amount, typically between two and four inches. The edges of the underlayment should also overlap any roof penetrations, such as vents or chimneys, to ensure complete coverage.
  5. Sealing: In some cases, seams or joints may require additional sealing to prevent water infiltration. This can be achieved using compatible sealants or adhesives recommended by the manufacturer.
  6. Finishing touches: Once the rubberized asphalt underlayment is installed correctly, securing the edges and corners with appropriate roofing cement or other approved sealants is crucial to protect against wind and water.

     #3. Non-Bitumen Synthetic Underlayment

Synthetic underlayments made from polypropylene or polyethylene, which are commonly utilized in a variety of products such as food storage containers and rope, are the non-bitumen alternatives. These synthetic polymers offer several advantages, including being lightweight and wrinkle-free, having impressive strength, and resistance to fungal growth. Depending on the manufacturer’s recommendations, they are typically considered moisture barriers and can resist UV damage for extended periods.

Non-Bitumen Synthetic Underlayment

 Non-Bitumen Synthetic Underlayment Installation

  1. Inspect the roof deck:  The roof deck should be clean, dry, and free of debris. If there are any holes or cracks in the roof deck, they should be repaired before the underlayment is installed.
  2. Measure the roof: The amount of underlayment you need will depend on the roof size. To ascertain the size of the roof, employ a tape measure to gauge the length and width, and then factor in an extra 10% to accommodate for overlap.
  3. Cut the underlayment to size: To achieve the desired size, you can employ a utility knife or scissors to cut the underlayment. Be sure to cut the underlayment to overlap by at least six inches.
  4. Install the underlayment:  The underlayment should be installed starting at the eaves and working your way up to the ridge. Ensure that the underlayment is overlapped by a minimum of six inches and securely fastened to the roof deck with staples or nails placed at 12-inch intervals.
  5. Flash the valleys: Valley flashing should be installed with a separate piece of underlayment. 
  6. Install the roofing material: The roofing material should be installed over the underlayment according to the manufacturer’s instructions.

Why is Roofing Underlayment Necessary For Your Roof?

Here are some of the reasons why roofing underlayment is an essential part of your roof:

  • Prevents leaks – Roofing underlayment is a water-resistant layer that helps to prevent water from leaking into your home. If water does get through the shingles, the underlayment will help to prevent it from reaching the roof deck.
  • Protects the roof deck – The roof deck is the wood or plywood that supports the shingles. Water can damage the roof deck without underlayment, leading to rot, mold, and other problems.
  • Extends the life of the roof –  Roofing underlayment can help extend your roof’s life by protecting it from the elements. Using synthetic underlayment can lead to long-term cost savings as you won’t need to replace your roof as frequently.
  • Provides a smooth surface for the shingles – Roofing underlayment creates a smooth surface for the shingles to adhere to. This helps to ensure that the shingles are properly installed.

The Cost Of Roof Underlayment

The installation cost of roof underlayment varies based on factors such as the selected material, accessibility, and the overall roof area. On average, the material itself is usually under $1 per square foot. It’s important to note that professional installation by a skilled roofer will incur additional expenses. Nevertheless, it’s highly recommended to entrust the installation to a professional for optimal results and to ensure the underlayment is installed correctly.

Choosing Suitable Roof Underlayment Material

Understanding different types of roof underlayment is crucial for a strong and durable roof. With options like asphalt-saturated felt, rubberized asphalt, and non-bitumen synthetic underlayment, choosing the right one is essential. When deciding on the best choice for your needs, consider factors like your roofing materials, the weather, and manufacturer recommendations for optimal protection.

Remember, proper installation is key! Consult with roofing professionals to ensure your underlayment performs its best. Whether you’re replacing an old roof or building a new one, Empire Roofing & Exteriors is here to help. Contact us at (225) 347-8877 for expert advice and top-notch roofing services. Give your roof the high-quality underlayment it deserves for long-lasting protection and performance.


A. Synthetic underlayment offers several advantages, including superior durability, increased tear resistance, enhanced moisture protection, and easier installation. It also tends to be lighter and more resistant to UV radiation than traditional asphalt felt.

A. Rubberized asphalt underlayment stands out for its excellent flexibility, exceptional weather resistance, and improved protection against water infiltration. Its unique blend of asphalt and rubberized polymers enhances performance in challenging conditions.

A. While it is possible to install roof underlayment yourself, professional installation is highly recommended. Experienced roofers have the expertise to ensure proper installation, maximizing the effectiveness of the underlayment and minimizing the risk of future issues.

A. Yes, roof underlayment plays a vital role in extending the lifespan of your roof. It acts as additional protection against water damage, ice dams, and wind-driven rain. By preventing moisture infiltration, it helps maintain the integrity of the roof structure and prolong its overall lifespan.

A. When selecting a roof underlayment material, consider factors such as the climate, local building codes, budget, desired level of durability, and the specific requirements of your roofing system. Consulting with a roofing professional can help you make an informed decision.