Synthetic Roofing Underlayment VS Black Felt

Key Qualities of Black Saturated Asphalt Felt Paper:

  • #30 or 30lb felt / 2 square roll, 3’ wide, 72 feet in length / 216 square ft.
  • #15 or 15lb lb felt / 4 square roll, 3’ wide, 144 feet in length /432 square ft.
  • Products normally have a simple paper label with minimum information.
  • Felt paper comes in rated and un-rated varieties. Rated versions usually specify ASTM test standards such as ASTM D226, 4869

ASTM stands for: American Society for Testing and Materials – these are standardized test that allow for cross comparisons between products.

  • Standard Felt is a non-rated felt with no testing.
  • Felt normally has no printed anchoring points, codes, brand or manufacturer’s name.
  • Felt paper can take on moisture and during the seasonal changes can buckle.
  • Felt normally has no marking printed on the product, a few have overlap lines.
  • It is recommended you stay with ASTM rated felts that meet your local building code.
  • Read the label carefully for important information. If there is very little written information – beware.
  • 2 & 4 square rolls of felt can weigh in the same range as synthetic rolls with 10 squares per roll. Synthetic rolls have superior strength and durability performance, and unlike felt come with a manufacturer’s warranty.
  • Felt offers NO warranty because it’s a price point product and you cannot identify a brand.


How to install Black Saturated Asphalt Felt:

Felt is usually fastened with staples, but in high-wind areas, plastic windstrips may be used along the edges to prevent tearing.

Felt may also be attached in high-wind areas using plastic caps and roofing nails. Plastic caps offer better wind resistance than staples, and help prevent leakage through the holes made by the fasteners.

Key Qualities of Synthetic Roof Underlayments (SRU)

  • Roll dimensions range from the norm 42”, 48” to hard to find widths of 50”, 60”, to 72”. As a general rule SRU have a gross 1,000 SF per roll (10 squares) regardless of width. (a square is 10’ x 10’ or 100 square feet in coverage)
  • Constructed of (1) coated blown films or (2) high strength coated wovens
  • SRU comes in an array of colors: gray, white, light gray, dark gray, blue, to black and others colors. A color is added to give the synthetic underlayment a consistent look.
  • Synthetic underlayments are superior to felt paper in that they are held to a higher standard when they carry an ICC listing number – (International Construction Code) as well as other performance code listings printed on the product.
  • Synthetic underlayments will have a product label normally with detailed product information, code listings, product testing results, and installation instructions; some include Safety Caution Statements.
  • SRU should list (one or more of the following:) ASTM D226, ASTM D4869, may show AC 188 or AC 207. Higher quality products will be ICC Code listed (International Construction Code). If not, beware you may not be getting what you paid for.
  • The Synthetic Roof Underlayment Institute (SRUI) is an organization founded to recognize those SRU brands that have met a higher product testing standards and other good business practices. For more information visit:
  • SRU may have printed overlap lines of 3” or 4”. Most SRU have printed anchor markings in the overlay area and in the field between the overlay lines.
  • SRU is commonly used under in sloped roof application 2:12 and higher. Common primary roofing materials are as listed: Metal, Shake, Shingle, Title, Slate, Ceramic, Asphalt Shingles and Clay & Concrete Title.
  • SRU will not buckle during seasonal changes.
  • Most synthetics are printed ALL the proper codes, brand names, anchoring points and association affiliations. Synthetics rolls normally have a product label, installation instructions, anchoring information and other vital information to include a WARRANTY. See the manufacturer’s website for more information. InterWrap TITANIUM synthetic underlayment’s have a Life Time Warranty that match the primary roof manufacturer’s exposure warranty. See InterWrap’s website for more details.


How to install SRU:

SRU is recommended to be fastened with plastic or metal caps with 1” ring shank nails or smooth shank roofing nails.



All data and information appearing on this site is anecdotal in nature, reflecting the contributor’s personal experience and not fact-based research and, therefore, to be used for information purposes only. Read full disclaimer