Roof Paper Under Shingles: A Guide to Roofing Underlayment

Roof paper under shingles refers to the layer of underlayment installed between the roof deck and the shingles. This foundational barrier protects against moisture, wind-driven rain, and ice damming, while also providing a surface for nail sealing and rollback protection during installation. In the United States, choosing the right roof paper—whether traditional tar paper or modern synthetic underlayment—can influence durability, ventilation compatibility, and long-term energy performance. This guide explains what roof paper is, the different types available, installation best practices, and how to avoid common mistakes that compromise a roof’s integrity.

What Is Roof Paper And Why It Matters

Roof paper, or roofing underlayment, is a protective layer installed over the roof deck before shingles are laid. It acts as a secondary moisture barrier and provides a smooth surface for shingle installation. In storms or wind-driven rain, underlayment can prevent water from seeping into the attic and structure. It also helps seal nail penetrations during shingle installation, reducing the risk of leaks. Proper underlayment selection aligns with climate, roof slope, and local building codes, making it a critical component of roof longevity.

Types Of Roof Underlayment

Underlayment comes in several forms, each with distinct performance characteristics. Traditional asphalt-saturated tar paper is economical and familiar to many builders, while modern synthetic underlayments offer higher tear resistance and weather resistance. Some products include reinforced or “peel-and-stick” membranes for improved sealant properties around fasteners and penetrations. The choice depends on climate, roof design, and installation method. In high-snow or high-precipitation regions, a more robust underlayment is often recommended to mitigate moisture intrusion.

• Tar Paper (Asphalt-Impregnated Felt): Inexpensive and widely used for decades, but more susceptible to tearing and moisture in extreme conditions.
• Synthetic Underlayment: Made from polyethylene or polypropylene, offering higher strength, lighter weight, and better moisture resistance.
• Self-Adhered Membrane: Peel-and-stick variants provide a continuous moisture barrier with strong adhesion, ideal for tricky roof transitions.
• Ice and Water Shield: Typically a self-adhesive membrane used in eaves or valleys to prevent ice damming and edge leaks.

When To Use Tar Paper vs Synthetic Underlayment

Tar paper has a long track record and remains a cost-effective option for basic roofs, especially on older homes or budget projects. Synthetic underlayment is preferred for new construction or remodeling in climates with heavy rainfall, snowfall, or rapid temperature changes. Self-adhered membranes are favored in areas with complex roof shapes, low-slope sections, or high wind exposure. Builders consider the roof slope, local weather patterns, and warranty requirements when selecting underlayment. Always verify compatibility with the chosen shingles and flashing details.

Installation Basics

Proper installation ensures the underlayment functions as intended. The process begins with a clean, dry roof deck and precise nailing patterns to avoid wrinkles and gaps. Overlapping seams must be oriented to shed water, typically with a prescribed offset. Fasteners should penetrate through the underlayment and into the roof deck at required intervals. In areas with wind uplift risks, additional fasteners or adhesive-backed sections may be necessary. For self-adhered membranes, removal of release film must occur carefully to avoid air pockets that can trap moisture.

1. Deck Preparation: Remove debris, repair damaged boards, and ensure the surface is dry.
2. Edge and Valley Details: Pay special attention to eaves, rakes, hips, valleys, and penetrations around chimneys and vents.
3. Seam Alignment: Align seams to prevent water from entering beneath the underlayment; use the recommended overlaps by product.
4. Nailing And Fastening: Use the correct nail type, length, and spacing; avoid overdriving nails and tearing the material.
5. Ventilation Compatibility: Ensure underlayment works with roof ventilation systems and does not block attic intake vents.

After installing underlayment, the next step is attaching shingles per manufacturer guidelines. Nails must be placed within specified zones to maintain shingle integrity and warranty coverage. In colder temperatures, heating or warming the underlayment slightly can improve handling, but follow product instructions to avoid compromising adhesion or surface integrity. Regular checks during the first year help identify loose edges or lifted seams that require minor repairs.

Common Mistakes And Maintenance

Common mistakes include selecting the wrong type of underlayment for climate conditions, improper seam overlaps, and insufficient fastening in high-wind regions. Skipping underlayment in some areas or relying solely on house wrap can lead to moisture intrusion. Maintenance is straightforward: inspect roof edges after storms, look for lifted seams or wrinkles, and replace damaged sections promptly. For homes in freeze-thaw climates, ensure the underlayment remains intact through seasonal expansion and contraction. Regular inspections help catch potential issues before they become leaks.

Code And Ventilation Considerations

Building codes in many U.S. jurisdictions specify minimum requirements for underlayment type, installation, and wind resistance. Homeowners and contractors should consult local codes to determine accepted products and installation practices. Ventilation plays a crucial role in the overall roof system; underlayment should not obstruct ventilation paths or create condensation zones in the attic. Some modern underlayments integrate with roofing vents and flashing systems to maintain air movement while providing a moisture barrier. Selecting products with recognized certifications can support code compliance and warranty protections.

Practical Tips For Homeowners

Choose underlayment based on climate, roof slope, and shingle type. In regions with heavy precipitation or wind, synthetic or self-adhered membranes offer superior protection. Maintain proper attic ventilation to complement the underlayment’s moisture barrier role. When in doubt, follow the shingle manufacturer’s recommendations and local building codes to ensure warranty validity and performance. Finally, consider professional installation for complex roofs or areas prone to wind uplift to maximize long-term durability.