Roofing Questions Synthetic Underlayment VS Felt

Roofing Questions Synthetic Underlayment VS Felt

For decades roofers in Atlanta have been installing felt paper as an underlayment when replacing roofs.  Felt is time tested and approved as a viable option with most residential roofing systems, but does this necessarily mean that felt is the best option in every case?  To answer this question we first need to understand what options exist for roofing underlayment and the value they provide.

Roofing Felt:

Generally speaking, 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, but this is the basic idea behind how felt works.  Felt is commonly sold in either 15# or 30# rolls measuring 36 inches wide.  Long ago a 15# role actually weighed 15 pounds, but over the years that has changed.

Synthetic Underlayment:

Synthetic Underlayment was developed 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.

Reasons to Use an Underlayment

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

  • Water Resistant (Not waterproof)
  • Protection from resins in the decking that can be damaging the asphalt shingles
  • Vapor protection
  • Temporary protection in the event of storm damage

Not every roof needs the best 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 at every nail hole. So which underlayment is better for your application?

Roofing Felt

If you are on a tight budget the best choice for your roof might be 15# felt.  Felt has been used for generations in Atlanta and has served its purpose well.  Is there a better solution than felt for most roofs? Sure there is, but felt is a great choice.  Also felts offer a great fire rating and are slow to burn.

Synthetic Underlayment

One of the main barriers to using synthetic underlayment for roofing contractors is the cost is higher per sq. ft. than traditional felt.  However, companies such as Interwrap have recently introduced new products that offer great durability and competitive prices.  Some of the major benefits to synthetic underlayment are:

  • Incredibly lightweight
  • Safer for roofers to walk on while installing shingles
  • Stands up to high winds in the event of shingles being blown off
  • Both water resistant and vapor resistant
  • Great for metal roof applications
  • Lays flatter on the roof decking which prevents the appearance of wrinkles that may appear where felt is used.

How Much Does Synthetic Underlayment Cost

Every single roof Fowler Homes quotes includes 15# felt as a base option, so there is no additional cost when it comes to felt; however a good quality roll of felt generally cost between $20.00-$30.00 dollars for material and covers around 400-440 sq. ft.  Synthetic underlayment varies widely between brands, job applications, and quality.  Most residential asphalt roofs can be roofed with products that cost around $150.00-$175.00 per roll installed, but each roll covers 1000 sq. ft.  Of course this price can be much different depending on the application so make sure you get an exact price for upgrading. Fowler Homes includes an option for upgrading to Synthetic Underlayment on every roof replacement we quote.  If you have more questions about synthetic underlayment vs. felt, feel free to email me at: or call me at (770)773-6830.

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