Why Is Felt Used As a Roofing Underlayment?

Felt is used as a roofing underlayment because it is cheap and easy to install, according to BobVila.com. It can vary in weight and is sometimes called felt paper or builder's felt.

Underlayment

Underlayment adds extra protection above the roof sheathing to prevent moisture from entering. Felt was the first type of roofing underlayment, introduced more than 50 years ago. The felt has a paper base that is either coated or saturated with asphalt, which strengthens it. The underlayment is rolled across the roof, then fastened in place by staples or nails.

Disadvantages

Problems with felt underlayment include a slippery surface, which can be less safe for installers to walk on, it can tear and it may have issues breathing, which can ultimately cause moisture to become trapped in the roof.

Modern Products

Modern underlayments consisting of polypropylene cost more but they breathe, are waterproof, lighter, resist mold, stay cooler and last longer. There are also self-adhering underlayments, which do not require fasteners to install.

References

• Bob Vila: Building a Tighter Roof with Roofing Underlayments