Tar Paper Under Shingles: Roofing Basics, Benefits, and Installation Tips

Tar paper, commonly known as roofing felt, plays a crucial role in protecting roofs when installed beneath shingles. This guide explains what tar paper is, why it is used under shingles, how it affects roof longevity, and practical installation tips for homeowners and professionals. By understanding its function, homeowners can better assess roof quality, navigate building codes, and ensure effective moisture control and insulation.

What Is Tar Paper And How Does It Work

Tar paper, or roofing felt, is a lightweight, waterproof layer made from asphalt-impregnated paper or fiberglass with bitumen coatings. Its primary purpose is to act as a moisture barrier between the roof deck and shingles. In older roofs, asphalt-saturated felt was common, whereas modern roofs often use asphalt-saturated fibrous felt or synthetic underlayment. The material slows water intrusion, helps with seam protection, and provides a stable surface for shingles to adhere to during installation.

Key points about tar paper under shingles: it adds an extra line of defense against leaks, improves airflow for drying, and contributes to temperature regulation by reducing radiant heat transfer into the attic space. In some climates, a second layer of underlayment is used for enhanced protection, especially in areas prone to heavy rainfall or snow.

Types Of Roofing Underlayment Used Beneath Shingles

Understanding the differences helps in selecting the appropriate underlayment for a given roof. The main categories are:

• Organic Felt (Roofing Felt) — A traditional option made from cellulose fibers saturated with asphalt. Comes in weights such as 15-pound and 30-pound per square and is less common on modern installations due to lower tear resistance.
• Synthetic Underlayment — Made from polyethylene or polypropylene. It is lightweight, tear-resistant, and offers better waterproofing and UV resistance. Many contemporary roofs preferred synthetic underlayment for durability and ease of installation.
• Rubberized Asphalt Underlayment — A self-sealing option often used around penetrations, valleys, and roof edges to provide superior water resistance and pliability in cold temperatures.
• Ice and Water Shield — A self-adhesive, rubberized asphalt product installed in vulnerable areas such as eaves, rake edges, and valleys to prevent ice dams and water intrusion in freezing climates.

Why Tar Paper Under Shingles Matters For Roofing Performance

The underlayment beneath shingles contributes to several critical performance aspects:

• Moisture Management — It acts as a secondary barrier if the outer shingles are damaged or blown off, reducing the risk of leaks reaching the interior.
• Seam Protection — It helps seal the gaps between shingles and around fasteners, minimizing water ingress through minor imperfections.
• DIY And Professional Install Safety — Provides a safer working surface during installation and assists with proper alignment of shingles.
• Code Compliance — Many building codes require specific underlayment types in certain climates to meet fire resistance, wind uplift, and moisture standards.

Climate Considerations And Building Codes

Regional climate heavily influences underlayment choice. In the United States, regions with heavy rainfall, snow, or freeze-thaw cycles often require more robust underlayment or the use of ice and water shield at critical locations. In milder climates, synthetic underlayment may suffice. Local building codes and manufacturer installation instructions are authoritative; contractors should check for updates to ensure compliance. Installing the correct underlayment improves energy efficiency by reducing heat gain in the attic and extends the life of the roof system.

Installation Tips For Tar Paper Under Shingles

Proper installation is essential to maximize the effectiveness of tar paper under shingles. The following best practices help ensure an effective roof assembly:

• Surface Preparation — Clean the roof deck of debris, fix protruding nails or fasteners, and ensure gaps are sealed before laying underlayment.
• Underlayment Over Existing Deck — Roll out from the eaves to the ridge with minimal wrinkles. Overlap edges according to manufacturer specifications, typically 19 to 24 inches for synthetic underlayment and 2 to 4 inches for traditional felt.
• Seams And Fastening — Use corrosion-resistant nails or staples as directed. Avoid over-tensioning the underlayment, which can cause wrinkles and pooling water at the seams.
• Valleys, Rakes, And Eaves — Reinforce critical areas with additional layers or self-adhesive ice and water shield in climates prone to ice dams. Ensure transition areas are properly flashed to prevent water intrusion.
• Ventilation Considerations — Maintain proper attic and roof ventilation, as inadequate ventilation can trap moisture and degrade underlayment faster.
• Weather Window — Install underlayment in dry weather with temperatures above the product’s minimum installation range to ensure proper adhesion and performance.

Common Problems And How To Avoid Them

Several issues can compromise tar paper under shingles if not addressed:

• Bunching Or Wrinkles — Can trap moisture and reduce seal integrity. Fix by smoothing the underlayment before shingle installation.
• Inadequate Overlap — Increases potential for leaks. Strictly follow overlap recommendations from the manufacturer.
• Damaged Or Missing Sections — Can expose the deck to water. Inspect after weather events and replace damaged areas promptly.
• Improper Sealing Around Penetrations — Causes leaks at pipes and vents. Use appropriate flashing and sealants compatible with underlayment material.

Maintenance And Lifespan

Tar paper under shingles typically lasts as long as the roof itself, assuming proper installation and typical climate exposure. Synthetic underlayments often offer longer lifespans and better resistance to UV light when exposed during construction. Regular inspections, especially after storms or hail, help identify deteriorating sections early. If a roof replacement is planned, contractors might upgrade to high-performance underlayment or ice and water shield in vulnerable areas to extend roof life and reduce maintenance needs.

Choosing The Right Underlayment For A New Roof Or Replacement

Making an informed choice involves considering climate, roof slope, deck type, and budget. For most modern American homes, synthetic underlayment with ice and water shield in low-slope intercepts and near eaves provides a balance of durability and cost. For homes in regions with severe winters, prioritize self-adhesive ice and water shield in valleys and eaves and ensure the overall underlayment meets the latest building code standards. Always consult the roof’s manufacturer guidelines and local building codes when selecting tar paper or alternative underlayment options.

Frequently Asked Questions

• Is tar paper required under shingles? Some climates and codes require it, while others permit synthetic underlayment. Always verify local code requirements and manufacturer recommendations.
• Can I install shingles directly over tar paper? No. Tar paper is the underlayment; shingles should be installed over it to ensure proper moisture management and long-term performance.
• How long does tar paper last? The lifespan depends on climate, material quality, and installation. Synthetic underlayment typically outlasts traditional felt, especially in sunny or wet conditions.