What Type of Roof Underlayment Do I Need?

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Between the plywood and tiles or shingles of your entire roof deck exists a powerful underlayment. Roofing underlayment, a thin sheet of material, acts as that extra layer of superhero protection for your home against the elements. From decades of roofing experience, we get to see both the good and the bad.

Back in the day, felt was your only option. Now, you have more options, but which underlayment is best for your roof? Here, we'll cover the different types of roof underlayment and how to make your choice for personalized weather protection.

What is roof underlayment?

Roof underlayment is a critical part of any roofing system. It's installed directly over the roof deck and beneath the tiles or shingles, acting as a secondary barrier that helps protect your home from water intrusion, heat, and wind. If any water was to find its way beneath the surface of your roof, the underlayment can help stop that moisture from reaching the wooden roof deck below. Without it, even a small leak can lead to rot, mold, or costly water damage over time.

Beyond just protecting your home from moisture, underlayment also adds a layer of insulation to shield against Arizona's excessive heat. It also helps to create a more even surface for shingle or tile installation, reduces sound transfer, and seals around flashing points for added weather resistance.

Why roof underlayment is important

Before we begin exploring the different types of roofing underlayment, let's take a closer look at why this layer matters so much in the first place.

Second line of defense against water

Your roof tiles are the first barrier against rain and wind, but they're not completely waterproof. If tiles are damaged, or wind pushes rain underneath them, the underlayment helps prevent water from reaching the roof deck and causing leaks, mold, or wood rot. In Arizona's monsoon season, this added layer of protection can make a huge difference in protecting your home.

Protects your home during the installation process

Underlayment also helps protect your home while the roof is being installed. If a storm was to hit before the tiles were secured in place, the underlayment keeps your exposed roof deck safe from moisture damage.

Holds shingles and tiles in place

A smooth and uniform underlayment surface helps shingles and tiles lay flat and stay properly attached. This is important for long-term performance, especially during periods of high winds or extreme heat.

Improves energy efficiency

Some underlayment can help reduce heat transfer through the roof, improving insulation in the attic space and helping to stabilize indoor temperatures. That means less strain on your HVAC system during those scorching summers and better energy-efficiency all year round (and potentially lower electricity bills!).

Meets local building codes and regulations

Most building codes require underlayment as part of a complete roofing system. Shingle and tile manufacturers also include it as a condition of their product warranties. This means that skipping underlayment doesn't just put your home at risk, but can also void your warranty and cause code compliance issues.

A look at roof underlayment types

The main options you have with roof underlayment are: synthetic, felt, rubberized asphalt, and Low-E insulation.

1. Synthetic underlayment: Newer, stronger, and cost-competitive

Synthetic underlayment is one of the most popular underlayment options, and for good reason. It's made from durable polymers and combines the best properties of traditional organic felt and synthetic products.

When we inspect roofs that are failing or leaking, the two primary contributing factors are tears in the felt or wrinkles caused by moisture. Synthetic underlayment is wrinkle-free, even when wet, and has a high tear strength.

Pros of synthetic underlayment

• Lightweight and easy to install

• High tear resistance and UV protection

• Excellent moisture barrier 

Cons of synthetic underlayment

• Typically more expensive than felt

• Can be slippery during installation.

2. Felt underlayment: The only option until now

Felt underlayment is made by soaking organic materials in asphalt (which is why it's also called asphalt-saturated paper). Because felt is a lower-cost and environmentally friendly option, it's commonly used to get the job done. Although water-resistant, felt underlayment may still absorb water when exposed to moisture.

Felt underlayment ranges from 15-pound to 90-pound rolls, indicating its thickness and asphalt content in pounds per hundred square feet. Despite a reduction in today's average roll weights, they are still categorized as 15-pound, 30-pound, 40-pound, and 90-pound. Naturally, a thicker felt will offer more durability.    

Pros of felt underlayment

• Inexpensive and widely available

• Suitable for many residential applications.

Cons of felt underlayment

• Absorbs water if left exposed

• More prone to tearing and wrinkling

• Heavier to install compared to synthetic options.  

3. Rubberized asphalt underlayment (aka SBS modified)

Rubberized asphalt is a self-adhered underlayment made of a fiberglass sheet with recycled rubber polymers superimposed on both sides. Its composition means that SBS-modified underlayment is very versatile and stable. It creates a waterproof seal against the roof deck, making it ideal for leak-prone areas like valleys, skylights, chimneys, and eaves.

Pros of rubberized asphalt underlayment

• Self-sealing means excellent water protection

• Great for extreme weather or high-risk areas

• Flexible and durable, even in extreme heat or freezing temperatures.

Cons of rubberized asphalt underlayment

• Higher upfront cost

• Must be installed carefully to avoid bubbles or wrinkles. 

4. Low-E underlayment (insulation)

Low-E, also called ThermaSheet®, acts as a thermal break and reflects radiant heat. If you want to get technical about it, Low-E insulation is insulation. Low-E is used in combination with your underlayment to stop heat from getting into your house or attic space. Without it, your air conditioner needs to work much harder to expel heat.  Low-E is extremely helpful in areas like Arizon awhere the outside temperatures routinely exceed 90 F. 

Choosing the right roof underlayment

Now that you know the types of underlayment available, let's look at some things to consider when choosing the right underlayment for your roof.

Climate and weather conditions

The first thing to consider is your local environment. In Arizona, our hot and dry climate calls for materials that can handle high temperatures and resist UV degradation. Synthetic underlayments tend to perform well in this environment due to their heat resistance and longevity under intense sunlight. Of course Low-E underlayment is probably the best choice for Arizona given its insulative properties.

If you live in a cold and wet climate, rubberized asphalt might be more ideal thanks to its waterproof and self-sealing properties.

Roof slope

The pitch of your roof might also impact your underlayment choice. For example, steep-sloped roofs can benefit from lightweight, easy-to-install synthetic underlayments as water runoff is fast and pooling is minimal. Low-slope roofs, however, might require stronger waterproofing, like rubberized asphalt, to prevent water intrusion and damage from pooling.

Compatibility with roofing material

Your roofing material also plays a role, since not all underlayments work with all types of roof. If you have asphalt shingles, most types of underlayments will be compatible, but synthetics often offer better performance and a cleaner installation. For metal roofing, look for underlayments designed to handle thermal expansion and prevent condensation. If you have wood shakes or shingles, rubberized asphalt offers the best protection against moisture intrusion.

Cost and budget

Of course, the cost of underlayment and your available budget is also an important consideration. Even though underlayment is far from being the most expensive part of a roof, prices can vary between the different types.

Felt is generally the most affordable underlayment type, however it has a shorter lifespan and can be less resistant to heat and UV. Synthetic roofing sits in the middle and offers good value, while rubberized asphalt is often the most expensive but offers a long-lasting option.

Durability and lifespan

Choosing a more durable underlayment can save you money on future repairs. In some cases, it might be worth making a bigger investment on a more durable underlayment that will last you longer.

Felt tends to be the most basic and affordable, but not built for long-term exposure. Synthetic roof underlayment is durable and resistant to tears, UV, and moisture. It's also mold-resistant and the best option if you plan to install solar panels in the future as it can withstand high temperatures. Rubberized asphalt also offers high performance, able to withstand extreme heat and weather conditions. It also self-seals around fasteners so offers excellent leak protection.

Which type of underlayment do you need?

The type of underlayment that's best for you depends on your priorities:

“I don't want to break the bank”

If your priority is a traditional, lower-cost roofing system, felt is a good option.  

The pros of felt include:

• More affordable

• Extra breathability (higher perm rating)

• Satisfactory results.

The cons of felt include:

• Less effective insulation in extreme temperatures

• More susceptible to ripping and tearing

• Prolonged exposure to water causes the felt to wrinkle.

Satisfactory installation requires the shingles to be installed as quickly as possible once the felt installation is complete. This is because if any moisture gets to the felt, the felt can wrinkle, creating an uneven roof surface that won't last. Thanks to the newer solutions available, felt is no longer the option we recommend on most roofing systems.  

“Give me the best home protection”

If you're concerned about premium roofing protection, leak prevention, and extreme temperatures, choose rubberized asphalt underlayment.

The pros of rubberized asphalt include:

• Stable with superior tear resistance

• Strong enough to go up against extreme weather conditions

• More heat resistant than felt

• Longer lasting than felt.

The cons of rubberized asphalt include:

• Higher initial cost

• Heavier than some options

• Not as much coverage per roll.

With rubberized asphalt, you get what you pay for. Although it is more expensive than other options, it's also the underlayment of choice for many homeowners due to its durability and water resistance properties. This means that you can enjoy a longer-lasting roof with proper installation.

“Lower my home's temperature”

If your goal is to lower energy bills, prevent degradation, and lower your home's temperature, choose Low-E underlayment.

The pros of Low-E include:

• Reduces energy usage

• Won't heat other roof materials

• Durable and easy to install.

The cons of Low-E include:

• Higher initial cost

• The need for an additional underlayment 

• Lack of accessibility (it may not be available in all areas).

Low-E ThermaSheet is gaining popularity as more people realize the potential energy bill savings and extended roof life.

“I need long-lasting with the option for solar panel installation”

If you need tear resistance and mold resistance and/or want solar panels installed in the future, choose synthetic underlayment.

The pros of synthetic include:

• Durable and tear-resistant

• Thin and lightweight, can conform to complex roof shapes

• More coverage per roll

• Withstands high temperatures even under solar panels.

The cons of synthetic include:

• Higher initial cost

• Lack of accessibility (it may not be available in all areas)

• Must be installed correctly for proper mold resistance.

This is a popular choice for Arizona homeowners for good reason! Although it's higher cost than traditional felt, synthetic underlayment is ideal for homeowners who want benefits similar to rubberized asphalt but also plan on solar power installation in the future.

In the long run, synthetic underlayment is cost-effective because of its durability and long-lasting nature. In other words, you get the best-of-the-best solution with the option to go solar later on. 

Still not sure which type of underlayment is right for you?

Other considerations — such as what materials are used for your roof system — could alter which type of underlayment is ideal for your situation. 

Don't worry about it! We've got you covered with a complimentary, no-obligation site evaluation where our roofing experts will look at your setup and present you with the best options for your home.

Request Your Site Evaluation.