When installing a new roof or replacing old materials, one of the most specific and critical questions contractors and DIY enthusiasts face is whether the drip edge goes on top or under the felt. This decision is not merely a matter of aesthetics; it is fundamental to the long-term integrity of the roofing system. The drip edge is the first line of defense against water intrusion, while the asphalt felt acts as a secondary barrier. Getting this sequence wrong can lead to expensive repairs down the line, as water can seep beneath the shingles and into the roof deck, causing rot and mold.
The Golden Rule: Drip Edge First
The overwhelming consensus among building manufacturers and professional roofers is that the drip edge must be installed before the underlayment, which is typically the asphalt felt. This sequence creates a protective shingle effect that directs water away from the fascia and into the gutters. If the felt is laid first, it creates a uneven surface that the drip edge cannot seal properly against. Water will easily find its way between the edge of the felt and the drip edge, negating the purpose of both components and allowing moisture to work its way up the underside of the shingles.
Step-by-Step Installation Logic
To understand why the drip edge goes on top, it helps to visualize the layering of the roof deck. The correct order from the bottom up is: roof deck, drip edge, underlayment (felt), and finally shingles. By nailing the drip edge tightly to the fascia board first, you create a solid, sealed perimeter. When the felt is subsequently rolled out, it overlaps the drip edge slightly. This overlap ensures that any water making it under the first row of shingles is caught by the felt and then guided down and over the drip edge, not behind it.
Consequences of Reversing the Order
While some older construction methods or specific regional exceptions might exist, installing the felt before the drip edge is generally considered a critical error. When the drip edge is installed afterward, it has to bear the brunt of the flashing process. The installer must bend the edge metal over the rolled felt, creating a gap between the felt and the metal. This gap becomes a highway for water, allowing it to travel freely up the roof deck and cause rot. Furthermore, nails driven through the felt to secure the drip edge can create new puncture points for leaks, bypassing the protective layer of the felt entirely.
| Installation Order | Water Management | Structural Integrity | Leak Risk |
|---|---|---|---|
| Drip Edge → Felt → Shingles (Correct) | Water is channeled away efficiently. | Creates a solid, sealed perimeter. | Low |
| Felt → Drip Edge → Shingles (Incorrect) | Water pools and seeps behind the barrier. | Creates gaps and weak points. | High |
The Role of Ice and Water Shield
Modern roofing often incorporates synthetic underlayments or ice and water shield membranes, particularly in colder climates or at the eaves. The rule of drip edge on top still applies rigorously here. In fact, with these newer materials, the installation is even more precise. The ice and water shield is a self-adhering membrane that must be carefully folded over the drip edge at the eaves. If the drip edge is not installed first, the adhesive of the shield cannot bond to the metal, creating a vulnerable seam where meltwater can penetrate during freeze-thaw cycles.
Manufacturer Warranties and Building Codes
Beyond the physics of water penetration, there are contractual and regulatory reasons to follow the standard. Most major roofing material manufacturers, such as GAF and Owens Corning, explicitly state in their installation guidelines that the drip edge must be installed prior to the application of underlayment. Failure to follow this sequence can void the warranty on the shingles. Additionally, modern building codes, including those in hurricane-prone regions, often reference the installation sequence directly. Inspectors will look for the drip edge being installed first; a deviation here can lead to a failed inspection and the requirement to tear the roof open to fix the mistake.
Practical Tips for the Roofer\
For the professional on the roof, the solution is straightforward to ensure a leak-free installation. Always begin by nailing the drip edge securely to the fascia, maintaining the correct overhang specified by the manufacturer. As you unroll the felt, allow it to overlap the drip edge by at least two inches. Secure the felt with cap nails, but avoid nailing directly through the drip edge slot if it compromises the metal's rigidity. By respecting this order, you ensure the roof functions as a cohesive system, where each layer works in harmony to shed water and protect the home for decades.
