Learn how Rhino Roofers can help you with a roof on your new home.
When most homeowners think about roofing, shingles are usually the first thing that comes to mind. While shingles play a vital role in protecting your home from the elements, they are only part of the roofing system. Beneath the shingles lies one of the most important—and often overlooked—components of a durable roof: roof underlayment.
Roof underlayment acts as a secondary barrier against water, moisture, and weather intrusion. It provides critical protection during storms, helps prevent leaks, and adds an extra layer of defense that extends the life of the entire roofing system. Understanding how underlayment works and choosing the right type can make a significant difference in your roof’s performance and longevity.
What Is Roof Underlayment?
Roof underlayment is a protective material installed directly onto the roof deck before shingles, metal panels, or tiles are applied. While shingles are designed to shed water, wind-driven rain, ice, and debris can still find their way underneath. Underlayment serves as the last line of defense, protecting the roof deck and interior of the home from moisture damage.
Without proper underlayment, even minor shingle damage can lead to leaks, mold growth, wood rot, and costly repairs. This hidden layer plays a major role in maintaining a watertight, durable roofing system.
Why Roof Underlayment Is So Important
Underlayment is essential because it protects areas that shingles alone cannot fully shield. Roof systems are exposed to harsh conditions over time, and underlayment helps mitigate the risks associated with aging materials and extreme weather.
Key benefits of roof underlayment include:
- Moisture protection: Prevents water from reaching the roof deck if shingles crack, lift, or fail
- Leak prevention: Acts as a backup barrier during heavy rain or wind-driven storms
- Added durability: Reduces wear on the roof deck caused by temperature fluctuations
- Temporary protection: Shields the roof during installation before final roofing materials are in place
In regions that experience heat, storms, or high humidity, underlayment becomes even more critical to long-term roof performance.
The Layers Beneath Your Shingles
A complete roofing system is built in layers, each serving a specific purpose. Understanding these layers helps explain why underlayment is so important.
- Roof Deck: The structural base of the roof, typically made from plywood or oriented strand board (OSB).
- Underlayment: Installed directly on the roof deck to provide water resistance and moisture protection.
- Roofing Material: Shingles, metal panels, or tiles that form the visible outer layer.
While shingles take the brunt of sun, rain, and wind exposure, underlayment is what protects the home if that outer layer is compromised.
Types of Roof Underlayment
There are two primary types of roof underlayment used in residential roofing today: felt underlayment and synthetic underlayment. Each has its own characteristics, advantages, and ideal use cases.
Felt Underlayment: The Traditional Option
Felt underlayment, often referred to as asphalt-saturated felt, has been used in roofing for decades. It is made from a base material (traditionally organic or fiberglass) that is saturated with asphalt to provide water resistance.
Benefits of Felt Underlayment
- Cost-effective: Generally more affordable upfront
- Proven performance: Long history of use in residential roofing
- Moderate water resistance: Provides basic moisture protection under shingles
Limitations of Felt Underlayment
Despite its long-standing use, felt underlayment has some drawbacks. It can absorb moisture over time, which may lead to wrinkling or tearing during installation. Felt is also heavier than synthetic options and can degrade faster when exposed to prolonged heat or moisture.
Felt underlayment may be suitable for budget-conscious projects, but it is often less durable than modern alternatives.
Synthetic Underlayment: The Modern Standard
Synthetic underlayment is made from advanced polymers engineered for strength, water resistance, and longevity. It has become increasingly popular due to its superior performance and durability.
Benefits of Synthetic Underlayment
- Enhanced water resistance: Designed to repel moisture rather than absorb it
- Greater durability: Resistant to tearing, stretching, and UV exposure
- Lightweight: Easier and safer to install
- Improved traction: Many synthetic products feature slip-resistant surfaces for installer safety
Because synthetic underlayment does not absorb water, it maintains its protective qualities even during extended exposure to rain or humidity.
Why Synthetic Underlayment Is Often Preferred
Synthetic underlayment provides consistent protection in extreme weather conditions and is particularly beneficial in climates with intense heat or heavy rainfall. Its strength helps prevent damage during installation, and its long lifespan supports overall roof durability.
Underlayment and Moisture Control
Moisture is one of the biggest threats to a home’s structural integrity. When water penetrates the roofing system, it can lead to mold growth, rotting wood, insulation damage, and interior leaks. Underlayment helps control moisture by acting as a water-resistant barrier between the roofing material and the roof deck.
In areas prone to storms or fluctuating temperatures, underlayment also helps protect against condensation buildup. Proper moisture control contributes to healthier indoor air quality and reduces the risk of long-term structural damage.
Ice and Water Protection
In vulnerable areas of the roof—such as valleys, eaves, and roof penetrations—specialized underlayment products may be used to provide additional protection. These self-adhering membranes help seal around nails and fasteners, offering enhanced leak prevention where water is most likely to collect or back up.
This extra layer of protection is especially valuable in preventing leaks caused by wind-driven rain or ice dams.
Choosing the Right Underlayment for Your Roof
Selecting the appropriate underlayment depends on factors such as climate, roof design, and the type of roofing material being installed. While felt underlayment can still be used in certain situations, synthetic underlayment is often the preferred choice for homeowners seeking long-term performance and peace of mind.
A properly installed underlayment system enhances the overall effectiveness of the roof, helping it withstand weather, resist moisture, and protect the home for years to come.
A Small Layer with a Big Impact
Although roof underlayment is hidden from view, its role in protecting your home is anything but minor. It serves as a critical safeguard against leaks, moisture damage, and premature roof failure.
By understanding the difference between felt and synthetic underlayment—and why this layer matters—homeowners can make more informed decisions about their roofing investment. A high-quality underlayment system doesn’t just support the shingles above it; it protects everything beneath them.