Should Drip Edge Go Over or Under Underlayment Complete Guide
Should Drip Edge Go Over or Under Underlayment?
One of the most common questions in roofing installation is whether drip edge should be installed over or under the underlayment. The answer is not the same for all parts of the roof and getting it wrong can lead to leaks, fascia damage, and premature roof failure.
The correct installation depends on whether you are working at the eaves or the rakes.
This guide explains the correct method, why it matters, and how to avoid costly mistakes.
The Short Answer
- At the eaves: drip edge goes under the underlayment
- At the rakes: drip edge goes over the underlayment
This is the standard method used across North America and required by most roofing codes.
Why This Difference Exists
The reason for this difference comes down to how water behaves on different parts of the roof.
Water Flow at Eaves
- Water flows directly down the roof
- Needs a clear path into the gutter
Wind Exposure at Rakes
- Water can be pushed sideways by wind
- Requires additional edge protection
Layering Principle
Roofing systems are installed in layers designed to shed water downward. The placement of drip edge and underlayment must follow this principle.
Drip Edge Placement at Eaves
Correct Installation
- Drip edge installed directly on roof deck
- Underlayment installed over drip edge
Layer Order at Eaves
- Roof deck
- Drip edge
- Underlayment
- Roofing material
Why This Works
- Water flows from underlayment onto drip edge
- Drip edge directs water into gutter
- Prevents water from reaching fascia
Drip Edge Placement at Rakes
Correct Installation
- Underlayment installed first
- Drip edge installed on top
Layer Order at Rakes
- Roof deck
- Underlayment
- Drip edge
- Roofing material
Why This Works
- Drip edge covers underlayment edge
- Prevents wind-driven rain from getting underneath
- Protects roof edge from uplift
What Happens If Installed Incorrectly
Drip Edge Over Underlayment at Eaves
Problem
- Water can run behind drip edge
Result
- Fascia damage
- Rot and mold
- Water infiltration
Drip Edge Under Underlayment at Rakes
Problem
- Wind can lift underlayment
Result
- Water penetration
- Edge leaks
Visualizing the Correct System
At Eaves
Water path
- Underlayment directs water onto drip edge
- Drip edge directs water into gutter
At Rakes
Protection system
- Drip edge shields underlayment edge
- Prevents water intrusion from sides
Code Requirements in North America
Most building codes require:
- Drip edge at both eaves and rakes
- Proper overlap of materials
- Correct layering sequence
Typical Requirements
- Minimum 2 inch overlap between sections
- Secure fastening every 8 to 12 inches
- Proper extension over fascia
Installation Tips for Best Results
Follow Correct Sequence
- Eaves first
- Underlayment second
- Rakes last
Ensure Proper Overhang
- Drip edge should extend slightly into gutter
Use Compatible Materials
- Match fasteners and metals
Maintain Straight Alignment
- Use chalk line for accuracy
Common Mistakes to Avoid
Using the Same Method for Entire Roof
- Eaves and rakes require different placement
Ignoring Building Codes
- Can lead to inspection failure
Poor Overlap
- Leads to leaks
Misalignment with Gutters
- Causes drainage issues
Special Cases
Metal Roofing Systems
- Follow manufacturer guidelines
- Placement may vary slightly but principle remains the same
Low Slope Roofs
- May require larger drip edge
- Ensure proper sealing
Retrofit Projects
- May require removing existing materials
- Ensure correct layering during replacement
FAQ Drip Edge and Underlayment
Does drip edge go over or under underlayment
Under at eaves over at rakes
Why is it different for eaves and rakes
Because water flow and wind exposure are different
What happens if installed wrong
Leaks fascia damage and reduced roof lifespan
Is this required by code
Yes in most North American regions
Can I fix incorrect installation
Yes but may require partial removal and reinstallation
Conclusion
Drip edge placement relative to underlayment is a fundamental roofing detail that directly affects performance and durability.
At eaves, drip edge must go under underlayment to direct water properly. At rakes, it must go over underlayment to protect against wind-driven rain.
Following this simple but critical rule ensures proper water management, prevents damage, and helps deliver a long-lasting, high-quality roofing system.