Roofing Underlayment: 15-lb and 30-lb Felt Paper
In this post, we are introducing a new series about roofing underlayment. Our focus will be on understanding its importance, how and why it works, and the various materials and components. As usual we’ll be drawing from our 20+ years of roofing experience in the Wichita, KS area. To start things off, we’ll be looking at the differences and benefits of 15-lb and 30-lb felt paper in protecting your home’s roof.
Why is underlayment important?
- It’s a second layer of protection if water penetrates the shingles.
- It protects the decking and inner structure of the home while the shingles are removed, especially if roof replacement takes longer than one work day.
- It provides slip protection for workers when they are installing shingles.
- It can increase the fire ratings of the home/roof.
The argument for using roofing felt paper
The benefits of using roofing felt paper far outweigh the consequences of not using it. Many codes, municipalities, and manufacturers require at least a 15 lb. felt underlayment for all roof installations or replacements.
You might hear some say, “If the felt paper is nailed, then it basically is ruined or is not applicable as a water proofing agent.” At S&A Roofing, we disagree with this statement. When nails are initially driven through felt paper, they are tight, and many roofing systems rely on properly functioning underlayment for the performance of the roof system. Since steep slope roofing systems are only designed to be water shedding, then a second means of water shedding protection is necessary for the performance of the system. And while driving nails does create holes in the felt paper, the nails remain in those small holes. If a shingle were to blow off without an underlayment below, a leak is certain! Felt underlayment can at least reduce the amount of water infiltration.
In S&A Roofing’s 20+ years of experience, we have spent a lot of time troubleshooting roof leaks that appear in the field of the roof or nowhere near any penetrations. Therefore, we do not hold that nails ruin underlayment as a valid argument.
The difference between 15-lb and 30-lb roofing felt paper
Historically, roofing felt paper was named for weight. 15-lb felt paper weighed 15 pounds per 100 sq. ft. (one roofing square) and 30-lb felt paper weighed 30 pounds per square. Felt paper is commonly produced with a certain number of recycled products and coated with asphalt. As technology has changed and manufacturing has improved, these are now lighter and have improved tensile strength. Many manufacturers offer upgraded felts with fiber glass reinforcement, making the felt paper extremely difficult to tear.
Some customers prefer 30-lb felt paper because it is a thicker product, less likely to tear, and should wear better over time. In addition, on steeper roof slopes 30-lb felt paper is necessary for the slip protection of the installer, and it is also less likely to tear during installation of the shingles.
Problem with your underlayment, need a roof inspection or quote?
Whether it be a leak repair, new roof install, or insurance claim filing, be sure to look for a roofing company who is willing to discuss the details including the underlayment. Remember, your roof protects your entire home and all that is within.
If you have any questions or if you are in the Wichita, KS area (including McPherson, Newton, and Hutchinson) and need a new roof or just an inspection, please consider S&A Roofing. Contact us any time at (316) 665-8482 or request a quote online.