Leaky Roof? Should You Use Felt or Tar Paper Underlayment?

Is your roof springing leaks every time it rains? You may need to replace the underlayment beneath your shingles. But should you go with traditional tar paper or modern roofing felt?

Underlayment creates a protective layer under your shingles to prevent moisture penetration. Both asphalt-coated tar paper and synthetic roofing felts serve this purpose. But there are some key differences to understand before deciding which is best for your roof.

What is Roofing Underlayment?

Underlayment, also called roof deck protection, is required by building codes under shingles, tiles, and metal roofing. This thin, water-resistant layer acts as a secondary barrier against rain, snow, and moisture infiltration.

There are several types of underlayment material to choose from:

• Asphalt-saturated felt or tar paper
• Non-asphalt synthetic underlayment or roofing felt
• Rubberized asphalt
• Self-adhering peel-and-stick membranes

Tar paper and roofing felt are two of the most common and affordable underlayment options.

Tar Paper vs. Roofing Felt Underlayment

What is Tar Paper?

Tar paper is made from heavy paper or fiberglass mat that is saturated with asphalt or bitumen. It is a very common type of underlayment, as it is inexpensive and easy to install.

The asphalt coating makes tar paper water resistant. However, it can become brittle and cracked in extreme heat. It also absorbs moisture in humid climates. While tar paper is still code approved, it may not be the most durable or weather-resistant underlayment material.

What is Roofing Felt?

Roofing felt refers to synthetic, fiberglass-based underlayments. It is also called building felt or synthetic underlayment. Roofing felt is made from fibrous material like fiberglass or polyester bonded with asphalt, acrylic or rubberized asphalt coatings.

Since roofing felt is made from woven fabric and not paper, it is lighter, thinner, and more flexible than tar paper. It can stretch and conform around roof features. Roofing felt is very moisture resistant. It holds up better to foot traffic and resists tears, cracks, and brittleness.

Comparing Durability

Tar paper consists of multiple thick layers of paper making it heavy and durable. However, the paper itself is vulnerable to moisture damage and tears over time.

Roofing felt is thinner but the synthetic fabric is designed to be tear resistant. It retains its flexibility and waterproofing properties longer than tar paper. Roofing felt can last up to 50 years, while tar paper may need replacing after 10-15 years.

Weather Resistance

The asphalt coating gives tar paper an advantage in terms of waterproofing. It forms a thick, protective barrier. However, once cracked or damaged from heat or humidity, the asphalt is less effective.

Roofing felt is also treated with waterproofing agents. The synthetic fibers will not degrade or become brittle. Roofing felt provides excellent leak protection even after years of sun, rain, snow and wind exposure.

Environmental Factors

Local climate is important in choosing underlayment type. In hot southern regions, roofing felt withstands heat better than tar paper. In rainy climates like the northwest, felt provides better long-term water protection.

In areas with heavy snowfall, synthetic felt resists ice buildup. Along coastal regions, salt air corrodes tar paper more quickly than roofing felt.

Talk with local roofing contractors about the best underlayment choices for your area.

Cost Comparison

On average, tar paper costs $75 to $100 per roll while synthetic roofing felts range from $150 to $200 per roll.

Tar paper is less expensive per square foot. But roofing felt requires less labor to install since it is thinner, lighter weight, and easier to cut and handle. The material cost savings of tar paper may be offset by higher labor fees.

In the long run, roofing felt is often a better value. The higher upfront cost will be recouped over time thanks to a lifespan double that of tar paper. If your goal is a durable, long-lasting roof, felt is worth the extra investment.

Installation Process

Proper underlayment installation is key to leak protection. Here is an overview of the process for each material:

Installing Tar Paper

• Roll out tar paper horizontally across roof deck.
• Overlap seams 2-4 inches and nail in place.
• Around valleys or protrusions, cut and flatten paper.
• Tape any tears or seams with roofing cement.

Installing Roofing Felt

• Roll out felt horizontally in same direction as shingles.
• Overlap seams 2-6 inches but do not nail.
• Use flexible, reinforced tape at seams and edges.
• Cut felt around vents; do not overlap.

Roofing felt requires fewer nails, cuts, and seams so it goes down faster. Less labor means lower project costs.

Ideal Use Cases

Here are some guidelines on when to use each type of underlayment:

• Use tar paper for temporary roof repairs or structures, like sheds.
• Choose tar paper for low-pitched and simple roofs without many slopes or valleys.
• Use roofing felt for permanent homes or important buildings.
• Select roofing felt for steep, complex roofs in windy or rainy climates.
• Pick roofing felt for homes in areas with extreme hot or cold weather.

There are several factors to help determine which underlayment is right for your particular roof:

• Roof type and materials - shingles, metal, tiles
• Climate and weather conditions
• Roof features - pitch, slopes, skylights
• Expected roof lifespan
• Budget

When in doubt, consult with a professional residential roofer. They can assess your roof and recommend the ideal underlayment.

Both tar paper and synthetic roofing felts meet code requirements. But for superior leak protection and durability, roofing felt is typically the best choice.