Tar paper, also known as asphalt-saturated felt, is a versatile construction material used primarily as a roofing underlayment and moisture barrier. Its roles span temporary weather protection during construction to secondary weatherproofing in walls and crawl spaces. Understanding where tar paper fits in can help builders choose appropriate underlayments and improve a structure’s durability against water and air intrusion.
What Tar Paper Is
Tar paper is made from natural or synthetic fibers saturated with asphalt or bitumen. This creates a flexible, tear-resistant sheet that can be rolled out over roof decks or wall sheathing. Traditional tar paper comes in various weights, commonly referred to as #15, #30, or heavier, indicating its density and thickness. The material acts as a barrier to moisture, wind-driven rain, and some air infiltration, while remaining relatively affordable and easy to install.
Common Uses Of Tar Paper
Tar paper serves several distinct roles in construction. The most common uses include:
- Roofing Underlayment: Placed over the roof decking before shingles or other roofing materials, tar paper provides a secondary barrier against moisture that can seep through gaps.
- Weatherproofing For New Roofs: During installation, tar paper protects the attic and interior spaces from wind-driven rain as the primary roofing system is completed.
- Moisture Barrier In Wall Assemblies: In some climates, treated tar paper is used under siding or as a temporary moisture barrier before a more durable weather-resistant barrier is installed.
- Temporary Moisture Barrier In Construction: On job sites, tar paper can cover exposed sheathing to shield it from precipitation until the final exterior is installed.
- Vapor Management: Depending on climate zones, tar paper can influence vapor diffusion, helping to manage condensation risks when paired with other building enclosures.
Benefits And Limitations
Benefits: Tar paper is inexpensive, easy to cut and install, and provides immediate protection against moisture and wind. It offers a simple, familiar solution for many roofing and siding scenarios, and it can be installed quickly on job sites with basic tools.
Limitations: Tar paper is not a long-term weather barrier in extreme conditions. It can deteriorate under UV exposure and heavy temperatures, especially if left exposed for extended periods. It is less durable than modern self-adhered membranes or high-performance house wraps, and it may require careful overlap and fastener placement to maintain continuity of protection.
Installation And Practical Tips
Proper installation ensures tar paper performs as intended. Key practices include:
- Overlap And Fastening: Overlap sheets by 2–4 inches along seams and secure with a consistent pattern of nails or staples to minimize gaps.
- Sealing Edges: Seal overlaps with compatible flashing tape or mastic in areas prone to water intrusion, such as around valleys, chimneys, and vent penetrations.
- Climate Considerations: In hot climates, ensure tar paper is not left exposed longer than necessary, as sun exposure can degrade the material. In windy areas, use additional fasteners at edges.
- Combination With Other Materials: Use tar paper as an underlayment beneath asphalt shingles, metal roofing, or tile, and pair it with a compatible top layer such as a higher-performance underlayment or house wrap for enhanced protection.
- Ventilation And Condensation: When used in wall assemblies, ensure proper ventilation and consider vapor-permeable options in climates prone to condensation to avoid moisture buildup.
Environmental And Safety Considerations
Tar paper contains asphalt-based products and should be handled with care. Workers should wear gloves to reduce skin contact and ensure proper ventilation when cutting or installing. While tar paper itself is not significantly hazardous, it should be disposed of according to local regulations for construction materials. When renovations involve old tar paper, beware of potential asbestos-containing materials in very old homes; have suspicious materials tested by professionals before disturbance.
Alternatives To Tar Paper
Advances in building science have produced durable and more water-resistant alternatives. Options include:
- House Wrap: Permeable or breathable wraps (like Tyvek) provide superior moisture management and air sealing.
- Self-Adhered Underlayments: Peel-and-stick membranes offer strong waterproofing and fewer seams, reducing the risk of leaks.
- Liquid-Applied Roof Membranes: For flat or low-slope roofs, these can provide seamless waterproofing without layers of felt.
- Synthetic Roof Underlayments: Advanced fibers offer higher tear resistance and longer service life under a variety of weather conditions.
Summary Of Key Points
Tar paper provides an affordable, quick-to-install moisture barrier for roofing and, in some cases, wall assemblies. It is most effective when used as part of a layered roofing system, paired with appropriate top coverings and flashing. While not as durable as modern underlayments, it remains a staple in many traditional construction projects and can be a practical option for certain climate and budget scenarios.