Roof Underlayment vs. Tar Paper

When roofing a newly-built house, many homeowners will focus on the exterior roofing materials and forget about the roofing underlayment. While it’s hidden below the roofing material, the underlayment plays a vital role. It adds another layer of protection to a roof.

With many roofing underlayment types available, you’re perhaps contemplating whether to invest in tar (felt) paper or synthetic underlayment. While both are great underlayment options, each has unique features, pros, and cons to consider before selecting any.

In this guide, we look at the features of the two types of roofing underlayment, including their pros and cons, to help you make an informed decision.

Synthetic Roofing Underlayment 

Synthetic roof underlayment consists of polyethylene or polypropylene weaved together with polymer to create a protective barrier on the roof. It’s a newer innovation that has taken over the roofing industry by storm due to its advanced features.

This roofing underlayment is an improvement of the tar paper underlayment. It is lighter and more robust than the latter, making it a popular choice among homeowners. Most synthetic underlayment has staples and roofing caps mechanically attached to them.

Notably, there are no standardized synthetic roofing underlayment materials. Meaning various manufacturers can make their products differently. As a result, you may have several synthetic underlayment materials with different levels of performance.

Pros of Synthetic Roofing Underlayment

If you are looking for an underlayment with improved resistance to water and other elements, you should choose the synthetic roof underlayment. It is moisture-resistant and has better protection against weather elements compared to tar paper.

Here are the other advantages of synthetic roofing underlayment.

  • Incredibly Durable: Designed with thermoplastic polymers, synthetic roofing underlayment is stronger in resisting wear and tear. It’s ideal for prolonged exposure to UV and moisture. They can also withstand boot traffic.
  • Longer Lifespan: It’s no doubt that synthetic underlayment has higher longevity than tar paper. Most manufacturers guarantee that it can last for more than 40 years. One factor that contributes to its longevity is its water resistance.
  • Available in Larger Rolls: Synthetic underlayment usually comes in larger rolls than felt paper underlayment. The felt paper comes in rolls of 2-4 roofing squares while synthetic underlayment in 10 roofing squares per roll.
  • Fast and Easy to Install: Since synthetic underlayment has more material per roll than tar paper, you’ll have fewer trips to the roof. That will save you a lot of time, allowing you to finish the job faster, especially if your roof is big.
  • Lightweight: Synthetic underlayment is lighter than its counterpart tar paper. It weighs about 2-4 pounds per roofing square, unlike felt paper that weighs around 15-30 pounds per square. That makes the installation process easier for roofers.
  • High Walkability: Another advantage of synthetic underlayment is that it offers a slip-resistant grip for enhanced walkability in wet and dusty conditions. That helps to improve the roofers’ safety while working on the rooftop.

Cons of Synthetic Roofing Underlayment 

Like any other roofing material, synthetic roofing material also has a few disadvantages.

  • More Costly: Synthetic underlayment usually has a higher price unit than tar paper underlayment. A plausible explanation is that they boast advanced roofing features. Besides, they come in larger rolls, making them more expensive.
  • Lower Permeability Rating: While this is an advantage for water resistance, it can also be a disadvantage. Moisture from within a building will not escape through the roof, calling for proper building and attic ventilation.

Tar Paper Underlayment

Also known as felt paper, tar paper is among the oldest roofing underlayment materials. It is manufactured by saturating a natural (natural fibers or wood cellulose) or synthetic (fiberglass or polyester) base with asphalt. That makes the material waterproof.

Most homeowners used this underlayment material in the mid and late 1900s. However, the introduction of newer innovations, like synthetics, is slowly phasing out tar paper underlayment. The good news is that it is still a viable underlayment option.

Notably, felt roofing underlayment is available in two forms: No. 15 felt and No. 30 felt. Each type has different strength and thickness. No. 30 felt is generally more robust, thicker, and less prone to wear and tear than the No. 15 felt underlayment.

Pros of Felt Paper Underlayment

Here are the advantages of felt or tar paper underlayment.

  • Relatively Cheaper: One roll of felt paper underlayment is less expensive than a roll of synthetic underlayment. If you are on a strict budget, the felt paper underlayment is a good option for you. 
  • Resistant to Water: Asphalt is water-resistant, helping a felt paper underlayment prevent water from penetrating its surface. That means no water will leak through a roofing structure. However, it has a higher permeability than synthetics.

Cons of Felt Paper Underlayment

Here are the drawbacks of felt paper underlayment.

  • Shorter Lifespan: A significant concern with felt paper underlayment is the short lifespan. It can’t last as long as synthetic underlayment. That’s why many roofers recommend that you use it with shingles, which have a lifetime of 15-20 years.
  • Fire Concerns: Asphalt is usually made from petroleum, making it a potentially flammable substance. Since manufacturers soak felt paper in asphalt during production, it makes the felt paper underlayment more prone to fire outbreaks.
  • Heavier Underlayment: Unlike the synthetic underlayment that is lightweight, tar paper underlayment is heavier. It can weigh anywhere between 15 and 30 pounds per square, while synthetic underlayment weighs around 2-4 pounds per square.
  • High-Temperature Issues: Felt paper underlayment is not very responsive to high heat. That’s because one of its components, asphalt, is a semi-solid form of petroleum. As a result, it’s more susceptible to higher temperatures.

Final Verdict

Now that you know the pros and cons of felt underlayment and synthetic underlayment, you probably wonder which is the right choice. Well, it depends on several factors, including how long you plan to stay in the house. If you find it tricky to decide, experts at Roof Master can help you choose what’s best for your home.

Contact us now to talk to one of our roofing experts.

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