What is synthetic underlayment and why do I need it?

Roofing felt has been around for over one hundred years. The purpose was to provide waterproof roof until the roof was complete and new shingles were installed. Other names for this include tar paper or roll roofing. The most common within the roofing industry is Synthetic Underlayment. Some people debate about the usefulness of the underlayment, and some even deem it unnecessary.

A great benefit to underlayment is that it can act as a moisture barrier. When the hot air rises through the house and reaches the roof, any moisture in the air can cause condensation on the underside of the shingles, so when you have synthetic underlayment it will help catch that moisture. This also helps prevent damage to the wood decking.

The moisture barrier is very important nowadays, we spend so much time in our homes, so cooking, bathing and even breathing can cause moisture build up and that needs to find a way out.

  • Is synthetic underlayment waterproof? Yes, underlayment is in fact waterproof. This provides a barrier between the decking and shingles so as not to deteriorate the shingles at a faster rate.

Roof Underlayment Types

3 main types of underlayment that roofing contractors can choose from when it comes to protecting the roof.

  1. Asphalt-saturated Felt

This used to be the most popular choice for roof underlayment until it was replaced by synthetics. It’s usually known as tar paper or felt paper and it can be made from various mixtures of asphalt, polyester, cellulose, or bitumen.

All types of underlayment are made with a basemat, which acts as a flexible base layer. In felt paper, this basemat achieves water resistance with a saturation of asphalt.

  1. Rubberized Asphalt

The most expensive option for roof underlayment due to higher amounts of rubber polymers and asphalt. This mixture creates a 100% waterproof seal but comes with a high price tag.

  1. Synthetic Underlayment

The most popular choice for roof underlayment, and with good reason. Made with an asphalt-saturated basemat and constructed with a mix of fiberglass, this product is not only extremely water-resistant, much stronger and more resistant to tears than other types of underlayment.


Underlayment sizes

There are 2 types of sizes #30 and #15. The only difference between the two is how strong they are.

#30 is the stronger of the two, throughout the roofing process the material is less likely to rip therefore creating a safer environment for the installers. However, #15 works just fine if installing a roof doesn’t take more than a day or two.


Underlayment is highly recommended

  1. It provides backup protection in the event of ice or snow damage. When the heat from your home melts the ice or snow on your roof, water can then get into the nooks and crannies and ultimately cause damage to your walls, and/or ceiling.
  2. Underlayment may also be required by the city for inspection. Without underlayment the shingle alone may not meet the Class A fire requirements. Your roofing contractor should be using underlayment comply with building codes.
  3. Protects the wood decking while the roof is being installed.
  4. Improves the look and framing effect. It provides a uniform surface that is even and helps prevent the wood decking showing through your shingles.
  5. Prevents wood resin stains. Over time wood tends to bleed small amounts of liquid that stain. The layer of underlayment will help block the resin and prevent stains.
  Underlayment and hot climates

The underlayment we use at Tomlin Roofing come in a cool white surface – up to 30 degrees cooler than other black underlayment. Our manufacture, CertainTeed also offers a UV protection feature in there DiamondDeck® Underlayment.


If you would like to learn more about our installation process then visit here>>https://tomlinroofing.com/residential-roofing/