Roofing Underlayment Options

roofing underlayment

Roofing underlayment is what lies between the shingles and the roof sheathing. We install it on the roof deck and it provides a secondary layer of protection from the elements, including rain, snow, and wind. There are two main types of roofing underlayment: felt and synthetic. Each has its own pros and cons, and your choice will depend on your geographical area, roofing materials used, roof design, budget, and what your roofing contractor suggests. Which is the best option for you? We break it down in this blog so you can get the best roofing options for your home. 

What Does Underlayment Do?

To decide which underlayment is the best choice for your project, you first have to understand the actual uses of underlayment and what they can and cannot do:

  • Water-resistance (not waterproof) 
  • Protection from resins in the decking that can damage the asphalt shingles
  • Vapor protection
  • Temporary protection in the event of storm damage

Not every home needs the best roof underlayment available on the market and not every budget can afford it. A standard asphalt shingle installation does not require the same vapor protection that might be needed for a metal or slate roof, but a steep roof installation might be safer with the better walking surface provided by some synthetic underlayment.

A common misconception by homeowners is that underlayment is waterproof and that their roof will leak without it. While underlayment is resistant to water, it is not self-sealing, so water can penetrate every nail hole.

What Is Roofing Felt?

Roofing felt is a felt paper that is soaked in asphalt and other water-resistant compounds to produce a membrane. Of course, it is a bit more technical than that, but this is the basic idea behind how felt works. They typically sell felt in either #15 or #30 rolls measuring 36 inches wide. Felt #30 is typically thicker, stronger, and less prone to tearing or ripping off during installation and poor weather. 

Pros Of Roofing Felt

If you are on a tight budget, the best choice for your roof might be felt. Felt has been in use for generations and has served its purpose well. 

The major advantage of using felt roofing underlayment is cost. It’s cheaper than the synthetic alternative, so if lower final costs are a large part of your bottom line, felt is your best option.

Additionally, felt is breathable. Felt underlayment, while water-resistant, is still breathable. This is a significant plus for your roofing materials, especially asphalt shingles. Since the plywood roof deck can breathe, it adds to the longevity of your shingles.

You can use traditional tools to install felt underlayment. Felt can be installed with common tools, but synthetic underlayment can’t.

Cons Of Roofing Felt

There are several disadvantages to using felt underlayment on a roof. The biggest one is that roofing felt can’t be left exposed for more than a few hours. The material may dry out or leach oils in the heat. Other cons include:  

  • It is prone to tearing in high winds and during the strain of installation. 
  • If exposed to moisture, the mat can absorb water and wrinkle the felt, making it harder for the shingles to lay flat. Therefore, shingles should be installed immediately after felt they install the roofing underlayment.
  • Felt underlayment weighs more, which can make it harder for roofing contractors to drag rolls of it up a ladder and onto a roof.
  • It has a slippery surface, which can sometimes make it more difficult to install. 
  • The weight also leads to less material per roll.  This means more potential seams instead of a single course with no laps.

What Is Synthetic Underlayment?

They developed synthetic underlayment as a felt replacement. By weaving together polypropylene and polymer, a water-resistant and vapor-resistant underlayment was created. This new underlayment is lighter and stronger than its predecessor. Different manufacturers make their products differently and may have different levels of performance, so it is important to do your research when selecting the right synthetic roofing underlayment for your home. 

Pros Of Synthetic Underlayment

One of the main barriers to using synthetic underlayment for roofing contractors is the cost is higher per square foot than traditional felt. Some of the major benefits to synthetic underlayment are that it is:

  • Incredibly lightweight. Synthetic underlayment is up to four times lighter than felt underlayment in some cases. 
  • Very tough and durable. It rarely tears and is suitable for extended UV and moisture exposure sometimes. 
  • Fast to install. Because there is more material per roll compared to felt, it results in fewer trips up the ladder for your roofer. This saves them time and helps the job move along faster. 
  • Safer for roofers to walk on while installing shingles. It’s also usually well-marked with guides and indicators where fasteners should be placed, which helps improve consistency and accuracy during installation. 
  • Stands up to high winds in the event of shingles being blown off.
  • Both water-resistant and vapor-resistant. They build synthetic roofing underlayments to repel water. 
  • Resistant to mold and mildew growth.  
  • Great for metal roof applications.
  • Likely to have fewer wrinkles because of laying flatter on the roof decking.
  • Synthetic roofing underlayment will last a very long time. 

Cons Of Synthetic Underlayment

Most synthetic roofing underlayments are competitively priced, compared to the cost of felt. However, the main drawback of synthetic roofing underlayment is the cost. The upfront investment in higher quality roofing materials is worth it because it will save you money down the road. You can’t put a price on the peace of mind knowing your roof has protection.

Final Thoughts

There are many factors to consider about the type of roofing underlayment to use. Synthetic roofing underlayment has many advantages over felt and may be a worthwhile investment to protect your roof and home from the risks of water and moisture infiltration. However, if cost is your chief concern, it is best to go with a felt roofing underlayment. 

Which one will you choose? We are here to help and answer any questions you might have! Call us at (636) 699-0449 to get started on your roofing project today.