A roof is more than just the shingles on its surface. It’s made up of an assortment of parts that all play individual roles, and some are hidden from sight — one of which is the underlayment. Despite not being visible from the curb, it plays a vital role in keeping the entire structure healthy and stable.

Roofing repairs and replacements are no cheap fix, which is why you want to be sure to use professional roofers to install the underlayment and overall roofing on your house. Both improper installation and poor-quality materials can cost you thousands down the line, so investing in a roofing company is a must.

Let’s take a closer look at the types of roof underlayment that exist so you know the ins and outs of your roof.

The Anatomy of a Roof

Unless you’ve built a house or a similar structure, you may be unfamiliar with the components of a roof.

The basic parts of most roofs include:

Rafters
Sheathing or deck
Underlayment
Shingles

The sheathing, also known as the deck, covers the rafters or frame of the roof. The frame is essentially the skeleton, and the sheathing materials are fastened on top. Plywood or oriental strand board are the most common materials for the deck. Since the deck is most often made of wood, and moisture can degrade or warp it, it needs an extra layer of protection. Underlayment on a roof is what protects the deck and inside from water damage.

Each part of the roof plays an essential role in the structural integrity and protection of your home. The rafters and deck provide the support for your roof, and the underlayment and shingles serve to protect your house from weather and damage.

What Is Underlayment on a Roof?

As its name suggests, the underlayment is the layer underneath all the roofing materials, meaning it’s installed under the shingles. It’s essentially a waterproof barrier that serves as an additional layer of water damage protection between the shingles and your roof deck. When all else fails, the underlayment is the roof’s last line of defense from weather intrusion.

If a hurricane, tornado or another extreme weather event occurs, your roof could be in danger. If your roof shingles fail by becoming damaged or separating from the house, the underlayment should protect your home from moisture and damage. The climate of your region may mean one type of roof underlayment is better than another. For example, some underlayments protect better from ice and snow, and others are more impervious to damage from the heat.

Types of Roof Underlayment

When it’s time to schedule a roof replacement on your old roof, you’ll also need to replace the underlayment. You have three options for underlayment — asphalt-saturated felt, non-bitumen synthetic and rubberized asphalt.

Asphalt-Saturated Felt

Asphalt-saturated felt is the oldest method of underlayment. It was the quintessential underlayment type until the appearance of synthetic materials. Despite its loss of popularity, it’s still relatively common and provides a reliable and strong underlayment with innate strength and water resistance. This option is also readily available, making it the most affordable of the three.

Felt underlayment can be fiberglass substrate or organic — it’s called organic because it has a cellulose base rather than a fiberglass base. The two options for asphalt-saturated felt are 15-pound and 30-pound underlayment. The 30-pound option is much thicker and provides better protection during harsh weather conditions.

Benefits of Felt Underlayment

Repels water: Even though rain can find its way between your roof shingles, the felt ensures water and moisture drains off the roof.
Provides snow and ice protection: Asphalt-saturated felt can provide superior protection against snow and ice. If you live in an area with frequent cold weather, the 30-pound felt will provide excellent protection.
Protects roof deck during installation: The felt ensures your roof deck isn’t exposed to the elements while installers place and secure the shingles.
Improves look and uniformity of shingles: Since your roof deck may not be perfectly straight, felt underlay can provide a uniform surface on which to lay the shingles.

Disadvantages of Felt Underlayment

Water absorption: Even though the felt underlayment is water-resistant, there’s a possibility that poor quality underlayment might absorb water and warp or damage the roof deck.
Loss of volatile compounds: The asphalt may lose some of its integrity over time, making the roof underlayment less sturdy and more moisture absorbent.
Ultraviolet (UV) light exposure: Extreme heat and exposure to the sun’s UV rays can reduce the effectiveness of the underlayment.

Non-Bitumen Synthetic

Non-bitumen synthetic underlayments replaced asphalt-saturated felt underlayment styles and are now the most commonly used type for both residential and commercial roofs. You can think of it as the direct upgrade from asphalt-saturated, thanks to its higher water resistance and durability. It’s also manufactured so that it can be fully applied to the entire roof.

Advantages of Non-Bitumen Underlayment

Synthetic: Since non-bitumens are synthetic, they’re more durable and lighter than other underlayments.
Anti-fungal: The synthetic material also means it’s less likely to promote fungus growth.
No degradation: Since there’s no asphalt in this type of underlayment, you don’t have to worry about the breakdown of essential compounds.
UV resistant: Non-bitumen underlayment isn’t sensitive to UV radiation, so it can withstand exposure for longer periods of time.

Drawbacks of Non-Bitumen Underlayment

Cost: This underlayment can be the most expensive on the market.
Requires careful application: If one were to install this underlayment as they would asphalt-saturated felt, it would undermine its water resistance and create moisture absorption issues.

Rubberized Asphalt

Finally, there’s rubberized asphalt, which is widely considered a premium underlayment material. It has all the benefits of asphalt-saturated and non-bitumen synthetic but is also completely waterproof since it has more asphalt and rubber polymer content.

The application of rubberized asphalt also sets it apart — it usually has a peel-and-stick fastening method, which means there’s no need to attach it to the roof and it’ll self-seal around any nails or staples. Because it’s so durable, you can leave this kind of underlayment exposed for quite a while without damaging your roof deck.

Pros of Rubberized Asphalt Underlayment

Completely waterproof: Because this underlayment type is made of rubber, it completely protects your roof from water.
UV resistant: Unlike asphalt-saturated felt, rubberized asphalt underlayment isn’t sensitive to the sun’s UV rays.
Extremely durable: This underlayment can withstand extremely high temperatures and generally lasts much longer than other types.
Easy to install: The peel-and-stick application means it’s easy to apply and it keeps installation costs down.

Cons of Rubberized Asphalt Underlayment

Different varieties: Since this paper comes in multiple forms, be sure to get one that complies with all building codes. For example, only some rubberized asphalt underlayments are resistant to fire.
Cost: Since it’s completely waterproof and highly resistant to damage, the cost for this underlayment will be pretty high.

Is Roof Underlayment Necessary?

Roof underlayment is an essential component in the construction of your house. It protects the roof deck from damage and can prevent leaks from heavy rain and snow. Additionally, it’s supposed to be breathable to allow any moisture that does infiltrate the deck to escape. If moisture gets under the underlayment, it can wreak havoc on your decking, causing warping of the wood, mold growth and leaks.

three common reasons roof underlayment fails

While the roof underlayment is a sturdy material, there’s a chance it can fail. A failed underlayment is a frequent roofing problem, and there are three common reasons the underlayment fails:

Poor Quality Materials

While most manufacturers produce quality underlayments, some materials are better than others. If your roofing service skimps out on the quality of the underlayment, it can have an enormous effect on your roof’s overall longevity. Since the underlayment provides water protection, poor-quality materials can damage the underlying roof structures and lead to water damage in your home.

Bad Installation

Even if you have the most expensive, highest-quality underlayment, you could face enormous costs down the line the installers don’t use proper installing techniques. For one, improper handling and walking on the underlayment during installation could damage it, which is why you want to be sure to hire roofing professionals. Additionally, if the roofers don’t know how to install each specific type of underlayment properly, you might be left with pockets in the roof that can let in moisture and damage your home.

Too Much Exposure

If your roof is old or suffers damage from wind or storms, it’s crucial to get a professional roofing inspection. While you may not be able to see it, any exposed underlayment from old or missing shingles can wear out, especially if you have felt underlayment. Over time, exposed underlayment may degrade, and then you’ll be left with a more expensive fix.

How to Choose the Best Roof Underlayment

While some roof underlayment types are more durable and waterproof than others, different roofing materials may perform better with certain underlayments.

Metal Roof

Metal roofs are easy to install and they hold up well to high winds, storms and debris. However, you should keep in mind that metal roofing has some qualities that make choosing the right underlayment all the more important. Metal roofs, because of the material, heat up quickly and don’t have great permeability. That’s why the underlayment should be breathable yet waterproof.

Felt paper underlayment is more permeable than synthetic, but it’s more common in older houses and it’s definitely more cost-effective. On the other hand, synthetic isn’t cheap, but you’ll get superior water protection and UV rays won’t damage the material like it does asphalt. Additionally, synthetic underlayment generally has a Class A fire rating, which many building codes require.

Shingles

Asphalt shingles are the most common roofing material, and they work well with all underlayment types. However, your region’s climate and the structure of your home may help you determine which underlayment is best.

For example, since asphalt-saturated felt is generally more sensitive to UV rays, it might deteriorate faster if you live in a hot, sunny climate. Non-bitumen or rubberized asphalt may be a better choice in that scenario, and they have the added bonus of better waterproofing. Alternatively, asphalt-saturated felt has better water transference because it isn’t completely waterproof. Steep-slope roofs often utilize this underlayment since it allows water to run off more easily. However, if your roof is flat, you may need a more waterproof option since water tends to pool on those kinds of roofs.

Shake

Shake roofing has great durability and curb appeal without being too costly. Shake roofing comes in both wood and asphalt varieties, and for both types, non-bitumen synthetic roofing is best. The high durability, matched with the total waterproofing, is the perfect choice for extending the life of your roof.

Both asphalt-saturated felt and rubberized asphalt carry the risk of degrading over time, which is why synthetic underlayment is usually better protection for shake roofing. Additionally, if you go with wood shake roofing, the waterproof underlayments prevent the wood from suffering water damage.

Is Your Roof Underlayment Old or Damaged?

A failed roof underlayment is a common roofing problem and can lead to a host of issues. Most roofs have a lifespan of a few decades, but improper installation, poor maintenance and extreme weather conditions can all lead to roof damage and sooner replacements.

Signs of a damaged underlayment include:

Leaks in the attic: Improperly installed or damaged underlayment can cause water to seep through the roof deck. Be sure to regularly check your attic for signs of leaks if you suspect roof damage.
Sagging roof deck: If your underlayment is causing poor water ventilation, the water-logged sections of your roof may begin to sag. This problem is serious and is especially common on roofs with low slopes that allow water to sit.
High energy bills: In addition to providing water protection, the underlayment adds extra insulation to your house. If your underlayment fails, it might be the reason for your high heating and cooling costs.
Seeing outside light in the attic: In extreme cases, your underlayment might be so damaged you can see outside light from your attic. If that’s the case, you’ll need to get a professional roofing inspection to see the extensiveness of the damage.

If you notice any of these signs of roof damage, it could be due in part to your underlayment. Whenever you replace your roof, you need to replace the underlayment to ensure it offers you the proper protection. If your underlayment is high quality and durable, it can protect you well from storm damage and high winds that could impact your shingles or other roof materials.

Contact Scro’s Roofing Company

Your roof protects you from the elements and is an essential component in the safety and comfortability of your home. Don’t trust your roof and underlayment installation to just anyone. Roofing repairs and replacements are expensive, so you want to make sure the company and materials help your roof last for a long time.

At Scro’s Roofing Company, we offer complete roofing services. We’ll help you pick the right roofing underlayment for your home so your new roof is completely protected from water intrusion and the elements. We use the highest quality materials, and our knowledgeable roofing experts will ensure a proper roof and underlayment installation on every job.

*updated: 8/2/21

We had significant hail damage due to the May 2016 hail storm in Cary, and warded off all the storm chasers that came through our area for 2 months after. I called Scro’s Roofing after the insurance adjusted had written off the roof, and they worked us into their busy schedule. Amazing job done by an amazing and hard-working crew. I was impressed by the way they used tarps to protect the landscaping around the house, and Patricia was pretty particular about cleaning up after the crew. Danny was a pleasure to work with, and he provided several improvements to our roof like a installing a chimney cricket and ridge vents. We used Moire black shingles and the roof looks...

Larry O. | Cary, NC

In life you get what you pay for and this is certainly true with Scro’s Roofing. There are so many “fly be night” roofing companies out there who do not have the long standing customer service and support that a local roofing company can offer. Everyone should take the time to educate themselves about the roofing process and the track record of the company, as this is a very larger investment and an area where you don’t want to cut corners. The team at Scro’s Roofing provided me with many educational links and never pressured me into a sale. They wanted to ensure that I fully understood the process and trusted that I would make an intelligent decision. This sharing...

Kevin A. | Wake Forest, NC

Scro’s Roofing installed a new roof on our home and everything went exactly as planned and scheduled. The installation crew covered all our plants and deck when removing the roof and then cleaned up perfectly when the job was done. We were kept informed all along the job from start to finish so we knew how and when everything would be done. I’ve never experienced a contractor, a company or an owner like Danny who worked with us on every detail. Further, we had gotten several other quotes with Scro’s being the best. This project couldn’t have been done more smoothly… We greatly appreciate Danny the owner and Sarah our scheduling contact. They both were there for all and every...

Joe V. | Cary, NC

We just had our roof done by Scro’s Roofing, and we are very happy with the results. Danny and his office were very helpful in answering all of my questions. I did a good bit of research beforehand, and after talking with Danny, I had a lot of confidence that they are up to date on best practices and latest materials. In particular, I liked that they hand nail the shingles, use a synthetic underlayment instead of tar paper, install a drip edge, and provide a 10-year labor warranty. The thing about getting a new roof is that most people may not find out whether the installer did a bad job or used inferior materials for 5-10 years when they...

Matt B. | Cary, NC

The big hail storm of May 2, 2016 did extensive damage to our roof (and Leaf-Guard gutters as well). Our insurance company appraised the roof and said it all needed to be replaced. My first choice was again Scro’s Roofing. I was not about to use one of the “storm chasers” that descended on our neighborhood like carpetbaggers from who knows where. Danny, the owner of Scro’s Roofing looked up my record from seven years ago and was able to give me an estimate almost immediately from the information he already had on file. Their estimate was within a couple percent of what our insurance had already written a check which made the decision to go with Scro’s Roofing again...

David C. | Cary, NC

I had a great experience working with Danny and his team. Danny even recommended a less expensive roofing product based on our needs. Sarah was so helpful and accommodating throughout the process. I wish all home repairs/renovations were this easy and professional. A wonderful company to work with!

Kate L. | Cary, NC