What Coil Size Do I Need for Hemmed Drip Edge?
Hemmed Drip Edge Coil Size Guide (Before Roll Forming)
Hemmed drip edge is a premium roofing flashing profile featuring a folded (hemmed) edge for improved safety, rigidity, and finish quality. It is widely used in residential and commercial roofing systems where durability and appearance are important.
The most critical starting point in production is selecting the correct coil size before forming — especially the coil width, which must account for hems and multiple bends.
For hemmed drip edge, coil size directly affects:
- Profile dimensions and fit
- Hem formation quality
- Edge strength and rigidity
- Roof edge coverage
- Production efficiency
This guide explains exactly what coil size you need before forming hemmed drip edge flashing.
What Is Included in “Coil Size”?
Coil size includes:
- Coil width (most critical)
- Thickness (gauge)
- Coil weight
- Coil inside diameter (ID)
- Coil outside diameter (OD)
- Material type and coating
All must match both profile design and machine capability.
1. Coil Width (Primary Factor)
The most important factor is the coil width before forming, based on the developed strip width.
For hemmed drip edge, this includes:
- Roof flange (top leg)
- Fascia leg (vertical drop)
- Drip return (kick-out edge)
- Hemmed edges (critical additional material)
- Bend allowances
Typical coil width ranges:
- 250 mm – 350 mm → small residential profiles
- 350 mm – 550 mm → standard hemmed drip edge
- 550 mm – 800 mm+ → large or commercial flashing
👉 Coil width must include extra material for hems, which is often underestimated.
2. Thickness (Gauge)
Hemmed profiles require material that can fold cleanly without cracking.
Typical ranges:
- 0.3 mm – 0.5 mm → aluminum (very common)
- 0.4 mm – 0.6 mm → standard steel flashing
- 0.6 mm – 0.9 mm+ → heavy-duty applications
Thickness affects:
- Hem quality
- Bend performance
- Edge strength
- Durability
3. Coil Weight
Coil weight depends on production setup.
Typical coil weights:
- 0.5 – 2 tons → manual or small production
- 2 – 5 tons → standard roll forming lines
- 5 tons+ → automated high-volume systems
4. Coil Inside Diameter (ID)
The coil ID must match the uncoiler.
Common sizes:
- 300 mm – 400 mm → small coils
- 508 mm (20”) → standard
- 610 mm (24”) → larger systems
5. Coil Outside Diameter (OD)
OD depends on coil weight and thickness.
Typical OD:
- 800 mm – 1500 mm+
Must match:
- Uncoiler capacity
- Handling systems
- Production space
6. Material Type and Coating
Material selection is critical for both forming and durability.
Common materials:
- Pre-painted galvanized steel
- Aluminum (ideal for hemming)
- Coated steel
Material affects:
- Corrosion resistance
- Surface finish
- Hemming performance
Why Coil Size Is Critical for Hemmed Drip Edge
Hemmed drip edge requires precise material allowance for folding.
If coil size is incorrect:
- Hems will be incomplete or distorted
- Profile dimensions will be wrong
- Flashing may not fit properly
- Edge strength will be reduced
- Installation issues will occur
Accuracy is critical for both function and finish quality.
Hemming (Key Feature)
The defining feature is the hemmed edge:
- Improves safety (no sharp edges)
- Increases rigidity
- Enhances appearance
Hemming requires:
- Extra coil width
- Correct material thickness
- Accurate forming
Incorrect coil size leads to:
- Cracked hems
- Poor fold quality
- Dimensional errors
Common Coil Size Mistakes
Not allowing for hems
- Profile too small
- Hems cannot form properly
Incorrect width
- Flashing does not fit roof edge
Wrong thickness
- Cracking during hemming OR too flexible
Incorrect material
- Poor finish or corrosion resistance
Poor slitting quality
- Visible edge defects
Machine Matching (Critical)
Before ordering coil, confirm your machine supports:
- Coil width range
- Thickness range
- Maximum coil weight
- Hemming capability
- Material compatibility
👉 Coil size must match machine + flashing design
What Buyers Must Confirm Before Ordering Coil
Always confirm:
- Hemmed drip edge design (including hem size)
- Developed strip width (including hems)
- Thickness
- Material type and finish
- Coil weight
- Coil ID / OD
- Machine limits
Never estimate — always include hem allowance in calculations.
Final Thoughts
For hemmed drip edge, the coil size before forming defines profile accuracy, hem quality, and installation performance.
Getting the coil size right ensures:
- Accurate dimensions
- Clean, strong hems
- Proper roof edge fit
- Improved durability
- Efficient production
Hemming adds complexity — coil size accuracy is essential.
FAQ
What coil size do I need for hemmed drip edge?
You need the correct coil width, thickness, weight, ID/OD, and material type, including extra width for hems.
What is the most important factor?
Coil width — especially allowing for hemming.
Why is hemming important?
It improves safety, strength, and appearance.
Does thickness affect hemming?
Yes — too thick may crack, too thin may be weak.
Can coil size be adjusted during production?
No — it must be correct before forming.