What are the Different Types of Roof Underlayment?

When building your roof or making repairs, it is essential you know the different parts that make up the roof. For a task that will make you dip into your pockets, it is only fitting you know a thing or two about it. The roof underlayment is the layer between the shingles (the roof covering you can see from the top) and the roof decking (the layer just below your ceiling), which is made of plywood, step sheathing, or OSB.

Although this layer is invisible, there’s no doubt about its importance in roofing. Its function is to prevent weather elements from making it to the wooden boards if the shingles get compromised. Therefore, it is usually a waterproof layer. 

“Felt paper” is another name for roof underlayment. However, this synonym is a type of roof underlayment. Due to the popularity of this underlayment type, the names are used interchangeably. Another synonym is “ice and water shield.” That name is self-explanatory. Now that you know the roof underlayment let’s see why you need it.

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Why Do You Need a Roof Underlayment?

If you’ve ever done an extensive roof repair, you’ll know a lot of money goes into buying these materials and labor costs. Hence, it is essential to have the proper structures in place to prevent unnecessary spending.

In your fight against the elements, the roofing underlayment serves the following functions:

  • Saves you money: Having to make any repairs in your home could be exhausting and would definitely cost you a fee. However, if the rood doesn’t get damaged in the first place, you get to keep your money.
  • Serves as protection for the roof decking: The roof decking is the most susceptible part of the roof to damage. This is why it has two protective layers about it. So even if your shingle gets compromised, the underlayment helps protect the decking from damage.

Also, the underlayment protects the decking from damage even during the installation of the roof. Constant walking on the decking will definitely damage the wood. However, there’s an extra mechanical protection layer with the underlayment layer.  

  • Increases the life expectancy of your roof: As time passes, most of these roofing materials start to deteriorate and lose integrity. However, with a durable protective underlayment, you’re sure you can enjoy your roof for years without making any repairs.

Types of Roof Underlayment

 There are three types of underlayment used underneath the shingles. They include:

  • Asphalt-saturated felt
  • Rubberized asphalt
  • Non-bitumen synthetic

Now, let’s examine each and see the advantages and disadvantages of using them.

1. Asphalt-saturated Felt/Felt Paper

Felt paper is the most popular type of roof underlayment. As mentioned earlier, it is commonly used as the common name for underlayment due to its popularity. This underlayment usually has an organic or fiberglass base soaked in asphalt to increase its waterproofing ability. The organic base is the more common variant and has cellulose as its major component.

Felt underlayment

There are two types of felt underlayment which include the 15 pounds per hundred square feet or No. 15 felt and the 30 pounds per hundred square feet or No 30 felt. The No. 30 felt is more durable and thicker; hence, it is more advisable for use in housing.

If you’re looking for a low-budget underlayment, you can’t do better than asphalt-saturated felt. However, this low price comes with some downsides. First, the asphalt-felt underlayment is quite heavy. While this might not really be significant, it could still increase your labor costs.

Also, felt paper isn’t as durable as the other types of underlayment. Once it absorbs water, it wrinkles and exposes your decking to the elements.


  • It is pretty easy to install. All it requires are roofing nails or staples.
  • Felt underlayment is quite effective as a moisture barrier when used in thick layers.
  • It is the most affordable of the three types of underlayment.


  • It absorbs water faster than other underlayment types. Hence, it has a higher tendency to get easily damaged.
  • It doesn’t fulfill modern ASTM standards.
  • Heat could cause evaporation of the volatile compounds in asphalt, causing the felt paper to lose its integrity.

2. Rubberized Asphalt

Credit: Pinterest

Just as the name implies, this underlayment comprises rubber polymers and asphalt. This is the only underlayment that is entirely waterproof. It is also very easy to install. It has a sticky waterproof base that a seal protects. The sticky base is simply installed on the decking, and the underlayment is ready.

This underlayment has a durable build with many other constituents added to make it stronger. Components like polyester or polyethylene confer anti-skid properties on its surface, making it safer for laborers to walk on it to install shingles. Mineral coatings also make it suitable for installation and use in harsh weather conditions. This makes it harder for the volatile constituents of the asphalt to evaporate. Some manufacturers also ass fiberglass to the mix.


  • It is entirely waterproof, hence offering more protection.
  • Rubber underlayment is resistant to UV radiations hence can be installed and used in harsh temperatures.
  • It is extremely easy to install.


  • It is expensive.
  • The installation also costs more.

3. Non-Bitumen Synthetic

Up to 12 times stronger than asphalt felt non-bitumen synthetic is one of the new breeds of underlayments used in roofing. It consists of a mixture of polymers such as polyethylene and polyester. They are incredibly light in weight and have non-skid properties. Manufacturers use these polymers to make the underlayment more flexible, durable, and resistant to damage. Its resistance to fungal growth also means any water that gets through from the shingles won’t breed microbes.

Its polymeric properties mean it is highly heat-tolerant and can be used in extreme conditions. In fact, you can leave the underlayment exposed to the elements for six months to one year (depending on the manufacturer’s recommendations) without any damage. Hence, if your shingles installation is delayed, you don’t have to worry about the integrity of the underlayment. Also, if you ever decide to take it out, they are recyclable and can be used in another housing project.



  • They’re quite expensive (worth up to 5 times the price of asphalt felt).
  • The market for non-bitumen synthetics is not regulated by ASTM standards.
  • Some manufacturers might not build these underlayment to meet current building code requirements.

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