Roof Underlayment 101: What is it & Why is it Important?

roofing underlaymentWhen you think of your roof, you probably picture either your tiles or shingles sitting on top of the main part of your house. This depiction wouldn't be inaccurate, but there's an unsung hero just below the surface that you shouldn't forget about. This hero is your underlayment, part of your overall roofing system that doesn't typically get paid much attention since it's out of sight, out of mind.

Roofing underlayment plays an essential role in ensuring your roof is healthy and your home is protected from the elements. In this blog post, we cover the basics of roofing underlayment and why it's important to keep this part of your roof in mind when thinking about its overall health and longevity.


What is roofing underlayment?

We'll start with a simple explanation of what, exactly, underlayment is. Roofing underlayment is a thin sheet of fabric installed between your roof plywood and your roof tiles or shingles. Its main job is to provide an extra layer of protection to your home from the elements. 


Why is underlayment important?

It might seem redundant to have underlayment when your tiles or shingles do most of the protective work. Some homeowners wonder if it's really necessary - to which we usually respond yes. Flat roofs and metal roofs are generally the exceptions to the rule. Below are our two top reasons why your roofing underlayment is important.

1. An added layer of protection

The most important function of your roof underlayment is adding another layer of protection. Consider it a second front to protect your home from monsoon storms or high winds. Your underlayment is the backup barrier between the inside of your home and Mother Nature. If some shingles or tiles are damaged or blow off when a monsoon rolls through the Valley, you'll be glad your underlayment is there as a backup. 

2. It helps to reduce heat

Living in Arizona, anything we can do to keep heat out of our home during the summer is a must. Many people don't know that what kind of underlayment they select can help reduce heat transfer into the home and result in HVAC units running more effectively. The new synthetic underlayment on the new roof below will help keep the roof's temperature down, save on electricity costs, and extend the life of the HVAC units and shingles.

old roofing underlayment

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Types of underlayment

The type of underlayment that's best for your roof largely depends on where you live and your local climate. Below are some of the most common options for roofing underlayment.

Synthetic Underlayment

Synthetic underlayment serves as a great waterproof vapor barrier between the wood roof deck and the roofing materials on top. In addition to its water resilience, synthetic underlayment is also a lighter underlayment option that contributes to healthy roofing systems. Synthetic underlayment is our preferred underlayment choice for shingle roofs. 

SBS Modified underlayment

This type of underlayment is comprised of a sheet of fiberglass with recycled rubber layered on both sides of the fiberglass, which gives it superior tear resistance and stability. This is our preferred underlayment for tile roofs since it's more durable, higher-quality, and holds up well in our wet monsoon summers.

Low-E ThermaSheet

Low-E ThermaSheet is a great second layer option that can help protect your roof while lowering roof temperature. Low-E protects your roof and your home from all three ways heat is transferred. The result is lower attic temperatures and a healthier overall roofing system. Learn more about Low-E and its numerous benefits in our dedicate blog.

Felt Underlayment

Felt underlayment is a common type of underlayment in some climates because it's a more affordable option than synthetic underlayment. This option is water-resistant, not fully waterproof, so it wouldn't be ideal in wetter climates. At Azul Roofing Solutions, we rarely use felt underlayment as there are higher-quality and more durable options available.


Damaged Underlayment 1What do I need to replace if my underlayment is damaged?

This answer depends on how much of your underlayment is damaged and what health your overall roof is in. If it's a localized area of damage, a qualified roofing company can replace that part of the underlayment and ensure the tiles or shingles on top of it are also healthy to prevent future damage.

If your underlayment is at the end of its life and showing it, we would recommend replacing all of your underlayment at once. This can help you save money in the long run by not paying for individual patches and repairs to it. If your tiles or shingles are also in need of replacing, then doing it all at once can also help save some money, too.


Underlayment is a critical component of an overall roofing system. If you think your underlayment is damaged or in need of a replacement, contact us for a free, no-obligation roof evaluation.

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