Drip Edge Over or Under Tar Paper Best Practices for Roofing

Drip edge placement relative to tar paper affects water shedding, roof integrity, and longevity. This guide explains when to install drip edge over or under tar paper, how each method impacts flashing, underlayment, and fascia protection, and how to choose the best approach for typical American roofs.

Understanding Drip Edge And Tar Paper

Drip edge is a metal or plastic strip installed along the eaves and rakes to direct water away from the fascia and prevent fabric wear. Tar paper, or roof underlayment, sits beneath shingles to provide a secondary barrier against moisture. The interaction between drip edge and tar paper influences wind-driven rain resistance, edge coverage, and the ease of shingle installation. Building codes in many U.S. locales specify drip edge installation to ensure proper water shedding, while underlayment guidelines vary based on climate and roof slope.

Over Tar Paper Installation

Placing the drip edge over tar paper means the drip edge is mounted on top of the underlayment. This arrangement is common when the roof sheathing and fascia are in good condition and the drip edge needs to catch water at the edge before it interacts with the tar paper. Benefits include easier inspection of fascia, simplified nail placement into the fascia through the drip edge, and a clean look where the edge can be visible after roofing is complete. Key considerations include ensuring the tar paper remains flat and adequately overlapped to prevent wrinkles that could trap moisture, and verifying that shingle overhang remains consistent to promote proper drainage.

When installed over tar paper, the drip edge typically receives fasteners that penetrate into the underlying fascia. Care must be taken to avoid puncturing the tar paper in a way that creates misalignment or leaks. The over-placement method is often favored in retrofits where existing tar paper layers are intact and the fascia is sound.

Under Tar Paper Installation

Installing drip edge under tar paper involves placing the drip edge beneath the underlayment, so water is directed by the tar paper first and then by the edge. This approach can enhance flash protection on the fascia by allowing the tar paper to act as an initial moisture barrier before water reaches the metal edge. It also helps protect the fascia from direct exposure, which may extend the life of painted or vulnerable finishes. Important notes include ensuring the tar paper is properly sealed at corners and valleys around the drip edge to prevent wind-driven moisture from slipping behind the edge.

Under-tar-edge installation is common in new construction or when the roof deck and fascia are being replaced, and it can require careful alignment to preserve the intended drip line. To maintain a neat appearance and robust waterproofing, installers often pair this method with a felt or synthetic underlayment that provides continuous coverage behind the drip edge.

Choosing The Right Approach For Your Roof

The decision between over or under tar paper depends on several factors. Climate plays a role: regions with high wind-driven rain or heavy snowfall may benefit from a configuration that minimizes exposed edges and maximizes moisture control. Roofing material type and installer experience influence the choice: metal drip edges often perform well in both setups, while some underlayment brands have specific recommendations. Fascia condition matters: damaged or rotted fascia might necessitate an over-tar approach for easier replacement, whereas sound fascia can accommodate under-tar installation. Retrofit considerations include whether existing tar paper must remain intact or if a full tear-off is planned, which could favor under-tar edge installation to align with new underlayment.

In general, if the goal is straightforward water shedding with minimal risk of edge exposure, installing drip edge over tar paper is a practical choice for many residential roofs. If fascia protection and layered moisture barriers are prioritized, under tar paper may be advantageous. Homeowners should consult local building codes and a licensed roofing contractor to confirm the best method for their specific roof assembly and climate.

Installation Tips And Common Mistakes

• Follow code and manufacturer guidance: Always verify local building codes and underlayment/drip edge manufacturer specifications before proceeding.
• Ensure clean, dry surfaces: Dry fascia and deck surfaces improve fastener holding power and edge alignment.
• Maintain consistent overhangs: Shingle overhang should match the drip edge projection to promote reliable drainage.
• Use proper fasteners: Choose corrosion-resistant nails or screws appropriate for the roof deck and drip edge material.
• Seal joints at corners and valleys: Apply flashing and sealants where necessary to prevent wind-driven infiltration behind the edge.
• Avoid damaging underlayment: If installing over tar paper, avoid compressing or tearing the underlayment, which could reduce its effectiveness.
• Inspect after installation: Check for gaps, misaligned edges, and secure fastening along the entire perimeter.

Common mistakes include installing the drip edge without considering tar paper overlap, which can create gaps; using incompatible fasteners that rust; and neglecting to seal at joints, which increases the risk of leaks. A meticulous approach that integrates drainage, wind resistance, and fascia protection will yield the best long-term performance.