Roofing Scissors: Best Tools for Cutting Underlayment
Quick Answer:
“Roofing scissors,” more accurately known as specialized aviation snips or heavy-duty metal shears, are $15 to $30 forged steel tools absolutely mandatory for precisely cutting galvanized drip edge, aluminum step flashing, and copper valley metal. Unlike standard utility knives which are used exclusively for scoring asphalt shingles, these compounded-leverage snips effortlessly slice through dense 26-gauge sheet metal without aggressively bending or warping the protective anti-rust coating. Attempting to cut flashing with a hacksaw will severely mangle the edge.
When a DIY homeowner prepares to roll out the heavy synthetic underlayment on their new roof deck, they naturally grab a standard utility knife from their toolbelt. However, they quickly discover a frustrating reality: pulling a small, sharp razor blade through 100 feet of highly engineered, woven synthetic polymer fabric is incredibly difficult. The razor blade snags, tears the material, goes dull in minutes, and requires you to kneel awkwardly on the steep pitch. To achieve long, perfectly straight, rapid cuts, professional roofers rely on a vastly superior tool: the heavy-duty roofing scissors.
Before you start cutting massive rolls of expensive underlayment, you need to calculate exactly how many rolls you need to buy. Use our Free Roofing Calculator right now to compute your exact roof surface area and generate a mathematically flawless material estimate in seconds.
Table of Contents
- What Are Roofing Scissors? (Tijeras para Roofing)
- Why Standard Utility Knives Fail
- The Power of the Micro-Serrated Blade
- Cutting Ice and Water Shield
- Conclusion: The Secret to Speed
- Frequently Asked Questions
What Are Roofing Scissors? (Tijeras para Roofing)
Roofing scissors (widely known on jobsites as tijeras para roofing) are not the delicate paper scissors sitting in your kitchen drawer. They are massive, heavy-duty industrial shears engineered to cut through thick, abrasive building materials.
- The Build: They are forged from heavy, high-carbon stainless steel. They usually measure 10 to 12 inches long, featuring massive, oversized rubberized handles that easily accommodate a worker wearing thick leather work gloves.
- The Design: The handles are heavily offset (angled upwards) from the blades. This brilliant ergonomic design allows the roofer to slide the bottom blade perfectly flat along the plywood roof deck while keeping their hand comfortably elevated above the abrasive wood.
Why Standard Utility Knives Fail
While a standard utility knife (a box cutter) is the perfect tool for scoring and snapping rigid asphalt shingles, it is terrible for cutting flexible synthetic underlayment.
Modern synthetic underlayment is not made of simple paper; it is woven from incredibly tough, tear-resistant polypropylene fibers. When you drag a straight razor blade across this woven fabric, the blade constantly snags on the tough cross-threads, resulting in a jagged, ugly, ripped edge. Furthermore, the microscopic sand and grit on the roof deck will instantly dull the tip of the razor blade, forcing you to constantly stop and change blades.
With heavy-duty roofing scissors, you simply open the massive jaws, bite down on the edge of the underlayment, and effortlessly glide the scissors forward to slice a perfectly straight, clean line across the entire 30-foot length of the roof in seconds.
The Power of the Micro-Serrated Blade
If you examine the cutting edge of premium roofing scissors (like the famous Clauss or Wiss brands), one of the blades is not perfectly smooth. It features micro-serrations.
These microscopic teeth are critical. When you try to cut a tough, slippery polymer fabric with a smooth blade, the fabric tends to slide forward and push out of the jaws. The micro-serrations instantly grip the tough synthetic fibers, locking the material in place while the opposite smooth blade slices cleanly through it with immense shearing force.
Cutting Ice and Water Shield
The true test of a roofing tool is cutting Ice and Water Shield. This is a heavy, thick membrane made of incredibly sticky rubberized asphalt, installed in the valleys and along the eaves of the roof.
If you try to cut this thick, sticky rubber with a utility knife, the tar instantly coats the razor blade, gluing it in place. The massive shearing power of the long roofing scissors allows you to slice cleanly through the heavy rubber membrane and the plastic release film simultaneously without getting bogged down in the tar. (Pro tip: If the scissor blades eventually get sticky from the tar, simply wipe them down with a rag soaked in WD-40 or mineral spirits).
Conclusion: The Secret to Speed
Drying-in a roof (covering it entirely with waterproof underlayment) is a high-stakes race against the rain. If you are struggling on your knees trying to tear through tough synthetic fabric with a dull razor blade, you are losing valuable time. By equipping your toolbelt with a massive pair of micro-serrated roofing scissors, you gain the mechanical leverage to slice perfectly straight lines while standing comfortably, drastically increasing the speed and safety of your installation.
Once the roof is fully waterproofed and the scissors are put away, you must ensure you have the exact amount of shingles ready to install over it. Head over to our Free Roofing Calculator right now. By inputting your roof’s basic dimensions, the tool will instantly output your exact total square footage, giving you the flawless data required to order your roofing materials.
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Frequently Asked Questions
Can I use roofing scissors to cut asphalt shingles?
No. While industrial shears are incredibly powerful, they are designed to cut flexible fabrics, rubber membranes, and thin plastics. If you try to cut a massive, heavy, stone-coated asphalt shingle with scissors, you will instantly dull the blades and likely snap the handle pivot point. You must use a specialized roofing utility knife with a hook blade to cut shingles.
What is the difference between tin snips and roofing scissors?
Tin snips (aviation snips) are specialized metal-cutting tools featuring very short, thick, jagged jaws designed specifically to bite through heavy-gauge steel drip edge and metal flashing. They are too short and aggressive to smoothly cut a 30-foot roll of fabric. Roofing scissors have long, 5-inch blades designed for rapid, straight cuts on flexible materials.
How do I sharpen roofing scissors?
Because the bottom blade features highly specialized micro-serrations, you cannot simply grind it on a whetstone, or you will destroy the teeth. You can only sharpen the top, smooth beveled edge using a fine-grit diamond sharpening rod. However, high-carbon industrial shears stay sharp for years; if they become severely dull or damaged by cutting wire, it is usually cheaper to buy a new $25 pair than to have them professionally machined.
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