What Is Roofing Underlayment and Why is it Important?

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We all know how important your home’s roof and its supporting components are to the structural integrity and overall beauty of your home — a roof helps keep the elements at bay and helps to insulate your home from the cold in the winter and excessive warmth in the summer.

A sturdy roof starts way beyond the surface or layer of shingles that you see from the outside. It takes several layers to perform these functions and no layer is more important than the underlayment, which helps keep your entire roof structure dry and protected from moisture.

What Is Roofing Underlayment?

Roofing underlayment is a barrier material that’s typically installed directly onto the wooden boards of your roof known as the roof deck. Depending on  your specific home, the skeleton of your roof is made up of rafters or trusses. The roof deck, also sometimes called roof sheathing, might be plywood, OSB, or step sheathing.

These boards are attached directly to the rafters or trusses to help stabilize the rafters or trusses and give structure to the entire roof.  The roofing underlayment is what goes on top of this sheathing material. It offers a secondary layer of protection from moisture intrusion should any rain or moisture get under your shingles.

Types of Roofing Underlayment

In general, there are three types of roofing underlayment: felt, self-adhered, and synthetic. Each has its own benefits and advantages, and the type you choose generally depends on what your roofing contractor is comfortable with and your local building codes and regulations.

Felt Underlayment

Felt underlayment is one of the oldest types of roofing underlayment. It’s commonly referred to as tar paper or felt paper and is made of an organic mat or paper that has been saturated with asphalt to help with water resistance.

For lightweight projects, a lightweight felt can be acceptable. However, it does tear easily, and if exposed to the elements during installation, can absorb water and wrinkle.

For homeowners who opt for felt underlayment, contractors may recommend a heavier felt, which is more durable than lightweight felt. As with any of the underlayment products, it can be applied in multiple layers for more protection.

Some roofing contractors commonly use felt underlayment when working with slate or tile shingles, while others may prefer self-adhered underlayment. It can depend on the region of the country.

Self-Adhered Underlayment

This kind of underlayment contains high percentages of asphalt and rubber polymers, making it a water-resistant solution for roofing underlayment.

Self-adhered underlayments have a sticky back, so they can adhere to the roof deck. This sticky backing helps create a waterproof seal between the roof deck and the underlayment. This type of underlayment is designed to protect the roof from damage in leak-prone areas such as eaves, valleys, vents, chimneys, and skylights.

Self-adhered underlayments are very useful in regions that receive severe winter weather. It also creates a non-skid surface, designed to make it safer for roofers to install, as it might be easier for them to walk around on.

Synthetic Underlayment

Within the last decade or so, synthetic underlayment has been a popular option for homeowners. While materials may vary by manufacturer, most synthetic roofing underlayment consists of multiple layers of various polymers woven together.

Synthetic underlayments typically have several advantages.

  • Tough, durable and tear-resistant
  • Lighter, with more coverage per roll (in comparison to most other types of underlayment products), reducing ladder trips
  • Secure walking surface
  • Clear, delineated lines and overlap guides for enhanced installation
  • Repels water and is inert to mold

Why Is Roofing Underlayment Necessary?

Roofing underlayment adds a second layer of protection that:

  • Safeguards your roof should your shingles tear-away due to high winds
  • Helps protect your roof deck from damage caused by ice dams during cold weather snaps
  • Shields your roof from bad weather during the installation process, prior to shingle attachment

To meet local building codes, your home’s roofing system must include a roofing underlayment product and roof covering. Additionally, shingle manufacturers require an underlayment as part of their warranty.

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