What is tar paper?

Tar paper is installed before shingles on a new roof.

Tar paper is a waterproof building material that serves as a base in civil construction. It works as a vapor barrier, preventing moisture ingress, as well as providing a thin layer of protection against airflow. Tar paper, also called felt, is made from cellulose fibers, glass fibers or polyester wool compressed into thin sheets. Tiles are treated with tar or asphalt to make them waterproof. Tar paper is typically installed under shingles, exterior cladding and hardwood floors.

Roofing tar paper is a waterproof building material.

Sold in rolls of various widths, weights, and lengths, tar paper is inexpensive and readily available at home improvement and building supply stores. The most common size rolls are 0.9144 meters wide by 50 or 100 feet (about 15.25 or 30.5 meters) long. It comes in 15 lb or 30 lb (6.8 or 13.6 kg) weights.

The weight designation means the weight of 100 square feet of tar paper. 15 lb (6.8 kg) tar paper is less durable than 30 lb (13.6 kg) tar paper and is used in less critical areas such as walls and floors. Tar paper is sometimes sand coated to prevent it from sticking while rolling.

The process of installing tar paper is called tar paper covering. It is normally installed on roofs over the sub-roof before installing shingles or gravel. In heavy rains, it is possible for water to be pushed under the tiles. The tar paper works as a secondary line of defense, preventing water from reaching the internal wooden structure.

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Tar paper is also applied as a coating on external walls. It is installed under the siding. This not only prevents water from reaching the internal wooden structure, but also helps to prevent the loss of heated or cooled internal air. Tar paper is sometimes used as a vapor barrier and dampening under hardwood floors, keeping the subfloor dry and helping to prevent hardwood floors from creaking.

Tar paper can help protect a building if the outside elements are lost or damaged. For example, if a shingle is ripped off during a storm, the underlying tar paper can protect the sub-roof until the shingle is replaced. While tar paper is an economical way to provide an additional layer of protection, it is not weather resistant. It will deteriorate if left exposed for long periods of time. Exposed tar paper should be covered as soon as possible to help maintain its integrity.

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