The best way to cut metal roofing is with four tools: aviation snips, sheet-metal shears, electric metal shears, or a nibbler. These tools shear the metal without creating excessive heat, sparks, or filings that can damage the coating and lead to corrosion.
Metal Roofing Cutting Methods at a Glance
| Cutting Job | Best Tool | Main Limitation |
|---|---|---|
| Short straight cuts | Aviation snips | Slow on long cuts |
| Long straight cuts | Electric metal shears | Can be difficult across ribs |
| Cuts around valleys, hips and penetrations | Nibbler or metal shears | Harder to guide in a perfectly straight line |
| Flat areas of standing-seam panels | Electric power shears | Not ideal across raised seams |
| Heavy-gauge panels | Manufacturer-approved cold-cut saw | Rougher edge and metal chips |
| Abrasive wheel or grinder | Avoid where possible | Heat, sparks and swarf can damage the finish |
Follow the installation instructions and warranty requirements for the specific roofing product. Cutting rules can differ between galvanized steel, Galvalume steel, aluminum, painted panels and insulated metal panels.
What Tools Do You Need?
For most residential metal roofing projects, gather:
- Tape measure
- Chalk line or marker approved for the panel finish
- Aviation snips
- Heavy-duty sheet-metal shears
- Electric metal shears or a nibbler
- Clamps or panel supports
- Work gloves
- Safety glasses
- Hearing protection for powered tools
- Soft brush or vacuum for removing filings
- Manufacturer-approved touch-up coating, if required
Aviation snips are commonly color-coded:
- Green handles: left-cut snips
- Red handles: right-cut snips
- Yellow handles: straight-cut snips
Choose the snip that matches the direction of the cut. Forcing the wrong type can deform the panel and leave a jagged edge.
How to Cut Metal Roofing Step by Step
1. Check the Manufacturer's Cutting Instructions
Find the panel brand, profile and coating before cutting. Some manufacturers allow a cold-cut saw with a suitable tungsten-tooth blade. Others prefer hand shears or power shears.
The instructions should also explain whether a cut edge needs touch-up paint, sealant, a hem or concealment beneath flashing. An exposed edge that is not treated correctly can reduce corrosion resistance and affect the warranty.
2. Measure the Cut Carefully
Measure the roof opening or required panel length at least twice. Mark the cut with a chalk line or a marker approved for the finish.
Allow for:
- Panel overlaps
- End laps
- Eave or rake overhang
- Valley and hip angles
- Hemmed edges
- Flashing coverage
- Manufacturer-required clearances
For a valley or hip, transfer the roof angle accurately instead of cutting the panel square.
3. Support the Panel on a Flat Surface
Place the panel on sawhorses or another stable, flat surface. Support the metal close to the cut line so it does not vibrate or bend.
Cut on the ground whenever practical. This makes the work safer and helps keep filings away from installed roofing. If the panel is prefinished, protect the visible surface from scratches and position it as the manufacturer directs. ASC Building Products recommends cutting prefinished sheets on the ground where practical and keeping hot particles away from coated panels.
4. Choose the Correct Cutting Tool
For Short Straight Cuts
Use straight-cut aviation snips or heavy-duty sheet-metal shears. Start at the edge of the panel and follow the marked line.
If closing the snips completely causes the panel to buckle, make several controlled cuts instead.
For Long Cuts Parallel to the Ribs
Use electric metal shears or a suitable nibbler. Power shears work well for long cuts across the flat portion of a standing-seam panel. They can be harder to control when cutting across ribs.
For Valleys, Hips and Penetrations
A nibbler or aviation snips usually gives you more control than a large saw. Cut gradually and keep the tool aligned with the marked line.
For a vent, pipe or other penetration, mark the opening before cutting. Start from the nearest panel edge where possible. If you need to create an internal opening, use the starting method specified for the tool. Avoid making unnecessary holes in the panel.
For Thick or Difficult Panels
Use a cold-cut saw only when the manufacturer allows it and specifies a suitable blade. A cold-cut blade creates less heat than an abrasive disc, but the cut edge may still be rough. The process also produces metal particles that must be removed immediately.
Should You Use an Angle Grinder or Abrasive Saw?
Avoid an angle grinder or abrasive metal-cutting disc on prefinished metal roofing unless the manufacturer specifically allows it.
Abrasive blades create heat, sparks and high-velocity metal particles. They can damage the paint or metallic coating, leave a jagged edge and push swarf into the panel surface. The particles can later rust and stain the finish.
ASC Building Products warns that saw cutting can leave rust-producing particles on the panel and that exposed saw-cut edges are more likely to corrode.
Do not use a torch on coated metal roofing. The heat can damage the protective coating and make the cut difficult to control.
How to Finish the Cut Edge
After cutting:
- Remove loose shavings and filings.
- Use a soft brush or vacuum instead of rubbing debris across the finish.
- Check the edge for sharp burrs or distorted metal.
- Trim small irregularities with sheet-metal snips.
- Apply only the touch-up product or edge treatment approved by the manufacturer.
- Conceal the edge beneath ridge cap, gable flashing, valley flashing or another trim component when the design allows it.
Do not leave swarf on the roof. Small filings can rust on the coating and stain the panel, even when the panel itself is intact.
Safety Precautions When Cutting Metal Roofing
Wear cut-resistant work gloves, safety glasses and sturdy footwear. Use hearing protection with electric shears, nibblers or saws. OSHA identifies flying particles, sharp sheet metal, noise and falls as roofing-tool hazards. Its roofing guidance also calls for fall protection when workers are exposed to fall hazards.
Follow these rules:
- Cut on the ground whenever practical.
- Keep other people away from the cutting area.
- Do not cut in wet, windy or unstable conditions.
- Never hold the panel in your hand while using a powered tool.
- Secure the panel and tool so the metal cannot shift.
- Use fall protection when working at a height where a fall hazard exists.
- Keep sharp offcuts away from walkways and dispose of them safely.
When Should You Hire a Roofing Professional?
Hire a roofing contractor if the roof is steep, high, difficult to access or requires complex valley, hip or flashing cuts. Professional help is also a sensible choice for standing-seam systems, concealed-fastener panels, insulated metal panels and large amounts of custom cutting.