Understanding Roofing Underlayment: What’s Beneath Your Shingles?

When people think about roofing, they often picture shingles, tiles, or metal panels—but what’s underneath is just as important. Roofing underlayment is a hidden yet crucial component of a well-built roof, providing an extra layer of protection against moisture, leaks, and extreme weather.

In this guide, we’ll explore what roofing underlayment is, the different types available, and why it plays a vital role in your home’s defense against the elements.

1. What Is Roofing Underlayment?

Roofing underlayment is a protective layer installed between the roof deck and the outer roofing material (shingles, tiles, or metal panels). It acts as a barrier against water, ice, and wind-driven rain, ensuring your home remains dry and secure.

Key Functions of Underlayment:

✔ Prevents water infiltration – Provides extra protection if shingles are damaged or lifted in a storm.
✔ Enhances roof durability – Reduces wear and tear on your roof decking.
✔ Improves fire resistance – Many types of underlayment add an extra layer of fire protection.
✔ Ensures smooth shingle installation – Creates a uniform surface for proper shingle attachment.

Even though underlayment isn’t visible once the roof is complete, it’s an essential component that can extend the lifespan and performance of your roof.

2. Types of Roofing Underlayment

There are three primary types of roofing underlayment, each with its own advantages and best-use scenarios.

A. Asphalt-Saturated Felt (Traditional Felt Paper)

✔ Made from: A combination of felt, asphalt, and fiberglass.
✔ Best for: Budget-conscious homeowners, older homes, and moderate climates.

Pros:
✅ Affordable and widely available
✅ Provides basic water resistance
✅ Works well in mild climates

Cons:
❌ Not as durable as synthetic alternatives
❌ Can absorb water and deteriorate over time
❌ Heavier and harder to install

While traditional felt underlayment has been used for decades, it’s gradually being replaced by synthetic options due to its limited lifespan.

B. Synthetic Roofing Underlayment

✔ Made from: Polypropylene or polyester-based materials.
✔ Best for: Homes in extreme weather conditions or those wanting longer-lasting protection.

Pros:
✅ Highly durable and resistant to moisture
✅ Lightweight and easy to install
✅ More resistant to tears, UV exposure, and mold

Cons:
❌ Typically more expensive than felt
❌ Not always required for low-budget roofing projects

Synthetic underlayment is becoming the industry standard due to its superior performance and longer lifespan.

C. Rubberized Asphalt (Peel-and-Stick) Underlayment

✔ Made from: A rubberized asphalt membrane with an adhesive backing.
✔ Best for: High-risk areas such as valleys, eaves, and around chimneys where leaks are more common.

Pros:
✅ 100% waterproof, ideal for ice and water-prone regions
✅ Self-sealing around nails for extra leak protection
✅ Extremely durable and resistant to cracking

Cons:
❌ More expensive than other options
❌ Requires professional installation

Rubberized asphalt is often used in combination with synthetic or felt underlayment to provide maximum protection in vulnerable areas.

3. Why Is Roofing Underlayment Important?

A. Protection Against Water Damage

Even the best shingles can’t stop all water infiltration, especially in storms with strong winds. Underlayment ensures water doesn’t seep into your home.

B. Adds an Extra Layer of Insulation

A properly installed underlayment helps regulate attic temperature, reducing heat buildup in the summer and keeping warmth inside during the winter.

C. Prevents Roof Deck Damage

Without underlayment, moisture can penetrate the wooden decking, leading to rot, mold, and weakened structural integrity.

D. Essential for Meeting Building Codes

Many building codes require underlayment installation for new roofs or roof replacements, ensuring homes meet safety standards.

4. How to Choose the Right Underlayment for Your Roof

When selecting underlayment, consider these factors:

✔ Climate: If you live in a wet or snowy area, rubberized asphalt underlayment offers the best protection.
✔ Roofing Material: Some materials, like metal, require specialized underlayment.
✔ Budget: Synthetic underlayment provides superior durability but at a higher cost than felt.
✔ Local Building Codes: Check regulations to ensure compliance with local roofing standards.

For best results, consult a professional roofing contractor to determine the right underlayment for your specific home and location.

Final Thoughts

Although it’s hidden beneath your shingles, roofing underlayment is one of the most important layers of your roof. It protects against moisture, extends the life of your roof, and improves overall durability. Whether you’re replacing your roof or installing a new one, choosing the right underlayment ensures long-term protection and peace of mind.

At Altru Roofing, we help homeowners select the best roofing materials for their climate and budget. If you’re planning a roof replacement or want to learn more about underlayment options, contact us today for expert advice and professional installation!