Underlayment Talk: Park City Roofer Explains No. 15 and No. 30 Underlayment

The underlayment is the layer beneath your roof that provides a second line of defense against the elements. Today’s underlayment materials are made out of polyester or fiberglass, replacing the asphalt-saturated housewrap-like felt that was commonly used in homes before the 21st century. Under the International Residential Building Code, asphalt shingles are required to have an underlayment.

A Park City roofing contractor offers two kinds of underlayment materials, No. 15 and No. 30 felt. You can immediately spot the difference between the two: No. 30 underlayment is thicker and more rigid than the No. 15. Normally, the No. 30 underlayment would appear as the better choice, but the No. 15 underlayment also has its own advantages.

No. 15 underlayment

Modern innovation has made the underlayment significantly lighter than before. A No. 15 underlayment, despite its name, weighs about 4 pounds per 100 square feet. It is also ideal for low-slope roofing or roofs with slopes of 14 degrees (3:12) and above.

The National Roofing Contractors Association (NRCA) recommends having two layers of this kind of underlayment for roofs with slopes of 14 degrees (3:12) and 18 degrees (4:12). The double protection will prevent leaks from seeping into the roofing structure. However, the NRCA also emphasizes that two layers of the No. 15 underlayment don’t equal a layer of the No. 30 underlayment.

No. 30 underlayment

A Park City roofer would recommend the No. 30 underlayment for heavy-duty roofing. Being the thicker underlayment, the No. 30 variant can take the full brunt of the elements better than the No. 15 variant. On the other hand, roofing experts say the No. 30 underlayment should only be used for shingles that weigh more than 240 pounds per square foot.

Heavy tiles such as clay or slate fall under the heavy-duty underlayment category and have the added benefit of being longer lasting than most other roofing materials. In addition, unlike the No. 15 underlayment, the No. 30 variant is installed only as a single layer due to its weight of 9 pounds per 100 square feet.

Ultimately, your choice of underlayment depends on factors such as the material of your roofing and the local climate. It’s best to consult with a roofing company like S&S Roofing that offers services such as installation, replacement, and roof repair Salt Lake City homes can benefit from.