Felt Paper

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Felt Paper

What is Felt Paper?

Felt paper is a building material used as an underlayment or moisture barrier to protect structures from water intrusion.

Description

Felt paper, also known as roofing felt or asphalt-saturated felt, is a flexible sheet material used in construction as a moisture barrier and protective underlayment. It is commonly installed beneath roofing materials or behind exterior wall finishes to help manage water penetration.

In construction, felt paper is typically made from cellulose or fiberglass mat saturated with asphalt. It is available in different weights, such as 15-pound and 30-pound felt, with heavier grades offering increased durability and moisture resistance. Felt paper is widely used under shingles, metal roofing, siding, and stucco applications.

Proper installation of felt paper is critical for effective moisture protection. Sheets must be lapped correctly and integrated with flashing and drainage details. While many modern synthetic underlayments are now available, felt paper remains a cost-effective and code-accepted option for protecting building assemblies.

FAQs

  • What is felt paper used for?

    It is used as an underlayment or moisture barrier beneath roofing and exterior wall finishes.

  • Is felt paper waterproof?

    It is water-resistant but not fully waterproof, which is why proper overlap and detailing are important.

  • What is the difference between 15-pound and 30-pound felt?

    30-pound felt is thicker and more durable than 15-pound felt.

  • Can felt paper be used on walls?

    Yes, it is often used behind siding or stucco as a weather-resistive barrier.

  • Is felt paper still allowed by building codes?

    Yes, felt paper is still code-approved for many roofing and wall applications.

Fun Fact

Felt paper has been used in construction for over a century, long before modern synthetic underlayments became available.

CSI Code

07 25 00

NAHB Code

720