When planning for a roof replacement or installation, your first thoughts likely go to the shingles, their color, and style. While these are important, a hidden layer underneath is vital for protecting your home and preventing future roof repairs. This guide explores the different types of roofing underlayment and their roles.
This material is installed between the shingles and the wood roof deck. It provides a critical secondary barrier against water intrusion. Understanding the common types of roofing underlayment will help you make an informed decision for your home’s protection.
What Exactly Is Roofing Underlayment?
Think of your roof as a complete system where every part works together. The shingles are the primary shield, but the underlayment is the essential backup. It’s a water-resistant or waterproof barrier applied directly to the roof sheathing, which is the plywood or oriented strand board (OSB) that forms the roof’s surface.
Its primary function is to prevent water that bypasses the shingles from reaching the roof deck. Wind can push rain under shingles, and ice buildup can cause water to pool and seep upwards. The underlayment provides reliable roof deck protection against moisture, preventing rot and structural damage.
Why You Can’t Afford To Skip Underlayment
Viewing underlayment as an optional expense is a significant mistake. It’s a fundamental component of a durable roofing system. Neglecting it can lead to expensive roof repairs in the future.
Strong winds can lift or remove shingles, leaving the roof deck exposed. With underlayment in place, your home remains shielded from rain until repairs can be made. In cold areas like Clay, NY, it’s your most effective defense against ice dams, which can cause severe water damage to attics and interior walls.
Furthermore, most shingle manufacturers require proper underlayment installation for their warranties to be valid. Building codes also specify its use for all new roofing projects. For a professional job, it’s not an option but a requirement.
A Look at the Types of Roofing Underlayment
You know underlayment is necessary, but which type is right for your roofing project? Three main options are available on the market today. The best choice depends on your budget, roof design, and local climate conditions.
Felt Underlayment (the Traditional Choice)
Felt underlayment, often called tar paper, is the classic choice for roofing. This asphalt-saturated felt is made from a paper or fiberglass mat soaked in asphalt for water resistance. It has been a standard in the industry for many decades.
It’s available in two main weights: No. 15 and No. 30. The No. 15 felt is lighter and more affordable but is also less tear-resistant. No. 30 felt is thicker, heavier, and offers greater durability and protection, making it a better choice for higher-end roofing materials.
While cost-effective, felt can absorb moisture and wrinkle if exposed to rain before the shingle installation is complete. It also becomes brittle over time from heat exposure, which can reduce its effectiveness. This option is a decent baseline but has been surpassed by modern alternatives.
Self-Adhered Underlayment (the Waterproof Seal)
This premium material is a composite waterproof membrane made from modified bitumen, which contains high levels of asphalt and rubber-like polymers. Its defining feature is a sticky adhesive backing that bonds directly to the roof deck. This creates a continuous, watertight seal that is highly effective.
This product is often called an ice and water shield because of its exceptional performance in preventing leaks from ice dams. It’s used on the most vulnerable sections of a roof. These areas include eaves, valleys, and around penetrations like chimneys, vents, and skylights.
The rubbery polymers in the membrane also create a seal around roofing fasteners, stopping water from seeping through nail holes. While it has a higher price point, its superior protection is invaluable in critical areas. Its installation requires a clean, dry surface for proper adhesion.
Synthetic Underlayment (the Modern Option)
Synthetic underlayment has gained significant popularity due to its advanced performance characteristics. This high-tech fabric is manufactured from woven polymers like polypropylene. The resulting material is incredibly strong, yet remarkably lightweight.
Synthetics present several advantages over traditional felt. They’re highly resistant to tearing, don’t absorb water, and won’t wrinkle if they get wet. This hydrophobic quality means they can be left exposed to the elements for longer periods if a project experiences delays.
Many roofing contractors prefer synthetics for safety reasons, as they often feature a nonskid surface for better footing during installation. They’re also fungus-resistant and hold up well to UV exposure. Some even come with preprinted nailing patterns to help guide the shingle installation for a cleaner look.
Underlayment Comparison at a Glance
To help you decide, here is a simple table comparing the three main types of underlayment.
| Feature | Felt Underlayment | Self-Adhered Underlayment | Synthetic Underlayment |
|---|---|---|---|
| Material | Asphalt-Saturated Paper/Fiberglass | Modified Bitumen with Polymers | Woven Polypropylene or Polyester |
| Water Resistance | Resistant | Waterproof | Resistant |
| Durability | Good | Excellent | Excellent |
| Cost | Low | High | Moderate |
| Best Use | Standard sloped roofs, budget projects. | Eaves, valleys, penetrations, low-slope roofs. | All roof types, long-term performance. |
Key Takeaways
Choosing the right underlayment is an important part of creating a long-lasting roof. It’s the component that protects your home’s structure from moisture damage. A discussion with your roofer will help determine the best materials for your specific needs.
By understanding these different types of roofing underlayment, you can actively participate in that conversation. At Dynasty Roofing, we’ve seen how using quality roofing materials at every stage makes a difference. We build every roofing system to protect your family and your investment for years to come.
