What Is Roof Underlayment

Roof underlayment is an essential component of your roofing system that provides an extra layer of protection between the roof deck and the shingles. It acts as a waterproof barrier, preventing water from infiltrating the roof and causing damage to the underlying structure. In this article, we will explore what roof underlayment is, its different types, benefits, installation process, common mistakes to avoid, maintenance tips, and how to choose the right underlayment for your roof.

What is Roof Underlayment?

Roof underlayment is a material that is installed directly on the roof deck before the shingles are applied. It typically consists of a felt-like material, often made of asphalt-saturated felt or synthetic materials. The underlayment serves as a secondary barrier against water penetration, protecting the roof deck from leaks and moisture damage.

Types of Roof Underlayment

There are several types of roof underlayment available in the market, each with its own set of characteristics and advantages. The most common types include:

Synthetic Roof Underlayment

One type of roof underlayment that has gained popularity in recent years is synthetic underlayment. Made from synthetic polymers, such as polypropylene or polyester, it offers superior durability, tear resistance, and water protection compared to traditional felt underlayment. Synthetic underlayment also has excellent UV resistance, which allows it to withstand prolonged exposure to sunlight without degradation.

Asphalt-Saturated Felt Underlayment

Asphalt-saturated felt underlayment, also known as tar paper, is the most traditional and widely used type of underlayment. It is made by saturating a fibrous mat with asphalt, which provides water resistance and durability. This type of underlayment is commonly used in residential roofing applications.

Rubberized Asphalt Underlayment

Rubberized asphalt underlayment is a more advanced version of traditional asphalt-saturated felt. It is made by adding rubber polymers to the asphalt, giving it improved flexibility, adhesion, and resistance to extreme weather conditions. This type of underlayment is often used in areas prone to high winds and heavy rainfall.

Benefits of Using Roof Underlayment

Using roof underlayment brings several benefits to your roofing system:

  • Waterproofing: The primary function of underlayment is to create a waterproof barrier, preventing water from seeping through the roof deck and causing leaks or damage.

  • Added Protection: Underlayment acts as an additional layer of protection against extreme weather conditions, such as heavy rain, snow, and wind-driven rain.

  • Extended Roof Lifespan: By protecting the roof deck from moisture damage, underlayment helps prolong the lifespan of your roof.

  • Enhanced Thermal Insulation: Some underlayment materials have insulation properties, reducing heat loss during the winter and minimizing heat gain in the summer.

How to Install Roof Underlayment

Installing roof underlayment requires careful attention to detail. Here is a step-by-step process for installing underlayment:

  1. Prepare the Roof Deck: Ensure the roof deck is clean, dry, and free of any debris or nails.

  2. Measure and Cut: Measure the length of the roof and cut the underlayment into manageable sections, leaving a small overhang for proper coverage.

  3. Start at the Eaves: Begin installing the underlayment at the eaves, securing it with nails or staples. Overlap each successive row, ensuring proper water drainage.

  4. Around Penetrations: Cut and fit the underlayment around any roof penetrations, such as vents or chimneys, ensuring a watertight seal.

  5. Valleys and Ridges: Pay extra attention to valleys and ridges, ensuring the underlayment covers the entire area for optimal protection.

  6. Secure the Edges: Use roofing cement or adhesive to secure the edges of the underlayment, preventing wind uplift.

  7. Inspect and Repair: Once the underlayment is installed, thoroughly inspect it for any tears or gaps and make any necessary repairs before proceeding with shingle installation.

Keep in mind that hiring an expert to install roof underlayment is highly recommended for ensuring proper waterproofing and protection, as their experience and skills can prevent costly leaks and damage. Their expertise guarantees a reliable underlayment installation that extends the lifespan of your roof and safeguards your home from potential water infiltration.

Common Mistakes to Avoid

While installing roof underlayment, it’s important to avoid these common mistakes:

  • Incomplete Coverage: Ensure the underlayment covers the entire roof deck, including valleys, ridges, and roof penetrations.

  • Improper Overlapping: Each row of underlayment should overlap the previous row to promote proper water drainage.

  • Damaged Underlayment: Inspect the underlayment before installation to check for any tears, wrinkles, or damage that could compromise its effectiveness.

  • Lack of Secure Fastening: Properly secure the underlayment with nails, staples, or roofing cement to prevent wind uplift and water infiltration.

Maintenance and Replacement

Roof underlayment requires minimal maintenance. However, it’s essential to periodically inspect the underlayment for any signs of damage or degradation. If you notice any tears, wrinkles, or other issues, it’s recommended to have the underlayment repaired or replaced promptly to ensure continued protection.

Choosing the Right Roof Underlayment

When choosing roof underlayment, consider the following factors:

  • Climate: Select underlayment that is suitable for your climate and can withstand the weather conditions prevalent in your area.

  • Roofing Material: Different types of roofing materials may require specific underlayment types. Consult with a roofing professional or manufacturer to determine the best match.

  • Budget: Consider your budget and choose underlayment that provides the necessary protection within your price range.


Roof underlayment is a vital component of a roofing system that provides an additional layer of protection against water infiltration and extends the lifespan of your roof. By understanding the different types of underlayment, installation process, and maintenance requirements, you can ensure your roof remains safe, dry, and well-protected for years to come.