Purpose of Tar Paper on Roof Underlayment
Tar paper on a roof serves as a critical layer in the traditional roofing system, acting as a secondary barrier that protects the structure from moisture intrusion. This article explains the purpose of tar paper, how it works within the roof assembly, and best practices for selection and installation. Understanding its role helps homeowners and builders make informed decisions about roof durability, weather resistance, and long-term maintenance.What Tar Paper Is
Tar paper, also known as roofing felt, is a thick, asphalt-saturated paper that comes in various weights and blends. It is installed over the roof decking and beneath the final roofing material, such as shingles or metal panels. The primary function is to provide a continuous water-resistant layer that slows water penetration during rain or snow events. In some modern roofs, synthetic underlayments have replaced traditional felt due to higher durability, but traditional tar paper remains common in many homes and renovation projects.Why Tar Paper Is Used
Moisture protection is the core purpose of tar paper. It creates a secondary barrier that helps prevent water from bypassing the roof covering if there are gaps, wind-driven leaks, or misaligned shingles. The underlayment also provides a cushion to the roofing material during installation, helping to prevent damage to the roof deck. Additionally, tar paper helps with temporary weather protection during construction and can improve the ease of flashing installation around chimneys, skylights, and vent penetrations.How Tar Paper Works Within the Roof Assembly
Tar paper sits directly on the roof deck and beneath the primary roofing material. It forms a continuous veil that minimizes moisture movement through the roof plane. When properly installed, it reduces the likelihood of capillary action drawing moisture into the attic space. The felt’s asphalt coating also adds a degree of wind resistance by helping to seal the joints where sheets meet. It is not a standalone waterproofing layer, but it significantly enhances the roof’s overall water resistance when combined with a robust final roof covering and proper flashing.Types Of Tar Paper And Standards
- Standard felt weight—common options include 15-pound and 30-pound felt, with 30-pound felt offering better tear resistance and longer life.
- Synthetic underlayment—not tar paper per se, but a modern alternative that provides superior water resistance, UV stability, and lighter weight.
- permeability and moisture resistance—higher-quality felts reduce the chance of moisture wicking and blistering under the roof covering.
In traditional homes, 15- or 30-pound tar paper remains widely used, while new builds may opt for synthetic underlayments. The choice depends on climate, roof pitch, and local building codes. Always check manufacturer specifications and local codes for the correct underlayment type and installation guidelines.Installation Basics
The installation sequence typically starts with removing existing roofing down to the deck and ensuring a clean, dry surface. Tar paper is laid horizontally from the bottom edge of the roof to the top, with a slight overhang at the eaves for drainage. Each sheet should overlap the one below by several inches to create a continuous barrier. Nails or staples secure the underlayment, and fastener placement should avoid ripples or loose spots. Special attention is paid to roof penetrations; custom cutouts and proper flashing are essential to prevent leaks.Common Mistakes To Avoid
- Inadequate overlap—insufficient overlap can create gaps that allow moisture intrusion.
- Over-tightening fasteners—driving nails too deep can tear the felt or create warping.
- Wrong underlayment for climate—using standard felt in high-humidity or high-wind areas may reduce performance.
- Skipping flashing details—poor flashing around chimneys, skylights, or vent pipes significantly increases leak risk.
Awareness of these mistakes helps ensure the tar paper performs as intended. Proper preparation, correct overlap, and attention to flashing details are essential for a durable roof assembly.Maintenance And Longevity
Tar paper itself is not meant to be a permanent, standalone waterproofing layer; its lifespan is tied to the roof system’s overall durability. Regular inspections after severe weather help identify wrinkles, tears, or loose edges. If damage is found, the underlayment should be repaired or replaced before installing the final roofing material. In some cases, particularly on older roofs, tar paper may show significant wear or blistering and warrant replacement alongside other roof components. Seasonal maintenance reduces the chance of moisture buildup and prolongs roof life.Environmental And Code Considerations
From an environmental perspective, older tar papers used more hazardous materials in some formulations. Modern products emphasize lower volatile compounds and more sustainable production practices. Building codes may specify minimum underlayment performance, including tear resistance and weather-tightness. In renovations, it is important to verify compatibility with existing roofing materials and to ensure the underlayment meets current code requirements. Homeowners should consult licensed roofing professionals to confirm product suitability and code compliance for their region.Choosing The Right Underlayment For Your Roof
- Assess climate and roof pitch to determine whether traditional tar paper or a synthetic underlayment is preferred.
- Check manufacturer installation guidelines for overlaps, nailing patterns, and flashing compatibility.
- Consider long-term maintenance and potential future roof replacements when selecting materials.
- Consult local building codes and a licensed contractor to ensure code compliance and durability.
Selecting the right underlayment is a balance between cost, performance, and climate resilience. For many residential roofs in the United States, tar paper remains a reliable and familiar choice when installed correctly and paired with proper flashing and final roofing material.Summary Of Key Points
- Purpose—adds moisture protection and a cushion under the final roof covering.
- Performance—works best when properly installed with adequate overlaps and flashing.
- Alternatives—synthetic underlayments offer improved durability in some climates.
- Maintenance—inspect after severe weather and repair defects promptly.
Understanding the purpose of tar paper on a roof helps homeowners evaluate options, ensure effective protection against moisture, and coordinate installation with final roofing materials for lasting performance. Proper selection, correct installation, and ongoing maintenance are essential to maximize the roof’s lifespan and resilience against weather.