The Complete Guide to Roof Felt: Why It’s Essential for Your Roof’s Longevity

When it comes to building or repairing a roof, most homeowners focus on the shingles or tiles they see on the surface. However, one of the most crucial yet often overlooked components is roof felt — a protective underlayment installed beneath your roofing material. Roof felt plays a vital role in protecting your home from water damage, improving insulation, and extending your roof’s lifespan.

In this ultimate guide, we’ll dive deep into everything you need to know about roof felt, including:

What roof felt is and its purpose
Different types of roof felt available
How roof felt is installed
Benefits of using roof felt in roofing systems
Common roof felt problems and how to avoid them
Alternatives to traditional roof felt
Maintenance tips to prolong roof felt life
Frequently asked questions about roof felt

Let’s get started!

What Is Roof Felt?

Roof felt, also called roofing felt or tar paper, is a protective underlayment material that is installed directly on top of the roof deck (usually plywood or OSB). It acts as a secondary barrier underneath shingles or other roofing materials to protect the roof structure from water infiltration.

Traditionally, roof felt was made from a base material of either organic felt or fiberglass mats saturated with asphalt (bitumen). This saturation makes the felt waterproof and resistant to wind and UV rays during installation.

Why Is Roof Felt Important?

Roof felt serves as an essential defense layer for your roofing system. Here’s why it’s critical:

1. Waterproof Barrier

Roof felt helps prevent water from penetrating the roof deck when shingles fail or during heavy rain. This reduces the risk of leaks and interior water damage.

2. Protection from Ice Dams

In colder climates, ice dams can form along roof edges, causing water to back up beneath shingles. Roof felt provides an extra barrier to protect the roof deck in these vulnerable spots.

3. Temporary Weather Protection

During roof installation or repairs, roof felt protects your home from rain until the final roofing material is applied.

4. Improves Shingle Performance

Roof felt offers a smooth surface that helps shingles lay flat and adhere better.

5. Adds Fire Resistance

Some types of roof felt provide additional fire resistance for your roofing system.

Types of Roof Felt

There are several types of roof felt available, each with its pros and cons:

1. Organic Felt

Made from cellulose fibers like wood pulp or recycled paper saturated with asphalt.
Heavier and thicker than fiberglass felt.
Provides good grip for shingles.
Prone to tearing and deterioration over time, especially when exposed to moisture.

2. Fiberglass Felt

Made from woven fiberglass mat saturated with asphalt.
Lighter and more tear-resistant than organic felt.
More durable and less prone to shrinkage.
Becoming the industry standard.

3. Synthetic Roof Underlayment

Made from polypropylene or polyethylene materials.
Lightweight, extremely durable, and resistant to tearing.
Provides superior water resistance and UV protection.
Usually more expensive but offers longer life and better performance.

4. Self-Adhered Modified Bitumen

Peel-and-stick membranes with a sticky backing.
Offers excellent waterproofing and air sealing.
Commonly used in vulnerable roof areas such as eaves and valleys.

How Is Roof Felt Installed?

Proper installation of roof felt is crucial to ensure it performs its protective function. Here’s a step-by-step overview of a typical installation:

Step 1: Roof Deck Inspection

Ensure the roof deck is clean, dry, and free of debris or protruding nails.

Step 2: Start at the Eaves

Lay the first course of felt along the eaves (bottom edge) of the roof. Overlap edges according to manufacturer guidelines (usually 2 to 4 inches).

Step 3: Roll Out Felt Horizontally

Roll out the felt horizontally across the roof deck, working upward toward the ridge. Each row overlaps the previous one to ensure water sheds properly.

Step 4: Secure the Felt

Use roofing nails or staples to secure the felt in place. Nails should be placed along the edges and center every 6 to 8 inches.

Step 5: Flashing and Valleys

In roof valleys, ice dam areas, and around vents, additional waterproof membranes or self-adhered underlayments are often used for extra protection.

Step 6: Inspect and Repair

Check the felt for tears, wrinkles, or gaps, and repair any defects before applying shingles.

Benefits of Using Roof Felt

Here are the key benefits of having roof felt as part of your roofing system:

1. Enhanced Waterproofing

Provides a critical secondary barrier against water infiltration.

2. Prolonged Roof Lifespan

Protects the roof deck from moisture damage, mold, and rot.

3. Improves Energy Efficiency

Acts as an additional insulation layer to reduce heat loss.

4. Fire Protection

Certain roof felts improve fire resistance ratings.

5. Cost-Effective Protection

Roof felt is a relatively inexpensive way to safeguard the roof structure.

6. Peace of Mind During Construction

Provides temporary protection if there’s a delay between roof decking and shingle installation.

Common Problems with Roof Felt and How to Avoid Them

Even though roof felt is durable, improper use or installation can cause issues:

1. Tears and Wrinkles

Avoid walking on felt unnecessarily during installation. Use synthetic felt for better tear resistance.

2. Moisture Trapping

Ensure roof decking is dry before installation. Good attic ventilation is essential to prevent moisture buildup.

3. UV Damage

Roof felt exposed to sunlight for prolonged periods can degrade. Complete roof installation promptly.

4. Poor Overlapping

Incorrect overlapping can lead to water infiltration. Follow manufacturer instructions carefully.

5. Nail Pops and Fastener Damage

Use the proper fasteners and avoid overdriving nails.

Alternatives to Traditional Roof Felt

Some modern roofing projects use alternatives for better performance:

Synthetic Underlayment: Offers superior durability and longer life than traditional felt.
Peel-and-Stick Membranes: Used for high-risk areas requiring waterproof seals.
Ice and Water Shield: Specialized membrane designed for protection in freeze-thaw climates.

While these alternatives may cost more upfront, they can provide better long-term value.

How to Maintain Roof Felt

Once installed under your roofing material, roof felt doesn’t require much direct maintenance since it’s protected. However:

Schedule regular roof inspections to check shingles and flashing for damage that might expose the felt.
Keep gutters clean to avoid water backup that can seep under shingles.
Maintain attic ventilation to prevent moisture buildup beneath the roof deck.
Address roof leaks promptly to avoid prolonged moisture exposure.

Roof Felt and Your Home’s Warranty

Many roofing manufacturers require proper underlayment installation to honor warranties. Using quality roof felt and installing it correctly helps ensure your shingles’ warranty remains valid.

How to Choose the Right Roof Felt for Your Home

Consider the following when selecting roof felt:

Climate: Areas with heavy rain or snow benefit from synthetic or ice and water shield products.
Roof Type: Steep or complex roofs may require more durable materials.
Budget: Traditional felt is cheaper but less durable; synthetic costs more but offers better protection.
Contractor Recommendations: Experienced roofers will know what works best locally.

FAQs About Roof Felt

Q: Can I install roof felt myself?

A: While DIY installation is possible for experienced homeowners, professional installation ensures correct overlapping, fastening, and coverage.

Q: How long does roof felt last?

A: Traditional felt can last 10–20 years under shingles; synthetic underlayment lasts longer.

Q: What happens if roof felt gets wet?

A: Wet felt loses effectiveness and can trap moisture, leading to rot. It should be installed on dry decking and covered quickly.

Q: Does roof felt help with energy efficiency?

A: Yes, it adds an insulating layer that can reduce heat loss or gain.

Q: Can I use roof felt with metal roofing?

A: Yes, though underlayment types may vary depending on metal roofing specifications.

Conclusion

Roof felt is a critical yet often unseen part of your roofing system that protects your home from water damage, improves durability, and enhances energy efficiency. Whether you’re building a new roof or repairing an existing one, investing in quality roof felt and professional installation is essential for long-term peace of mind.

If you’re planning a roofing project, talk to a trusted roofing contractor about the best roof felt options for your climate and budget. Proper installation today will save you money and headaches tomorrow.

Roof Felt