Utility Knife with Hook Blade

A utility knife is a standard cutting tool on almost every roofing job. Roofers commonly fit it with hook blades, which have curved, hook-shaped cutting edges instead of the pointed ends of the standard trapezoidal blade. Hook blades are designed for cutting with a pulling motion through flexible sheet materials such as roofing felt, underlayment, asphalt shingles and some membranes, as well as linoleum and carpet in other trades.

Why hook blades

• Pull cutting: the hook draws through the material as the roofer pulls the knife along a straightedge or chalk line, rather than pushing a point into it.
• Protection of the surface below: because the tip is shielded inside the hook, cutting a shingle or membrane laid on the roof is less likely to slice into the layer underneath than with a pointed blade.
• Back cutting of shingles: asphalt shingles are often cut from the back (the mat side), where the hook cuts cleanly through the asphalt and mat without dragging through the granules, which dull blades quickly.
• Reversible blades: like standard trapezoidal blades, most hook blades have two cutting ends, so the blade can be turned when one end is dull.

Knife types

• Retractable knives let the blade be withdrawn into the handle when not in use, reducing accidental cuts.
• Fixed-blade knives hold the blade rigidly for heavy cutting.
• Folding knives fold the blade into the handle for carrying.
• Many models store spare blades in the handle and allow tool-free blade changes.
• Hatchet-knife combinations and holsters are sold for roofers.

Use and safety

Hook blades dull quickly on granule-surfaced products, and a dull blade needs more force, which increases the chance of slips. Practical guidance from tool makers and safety bodies includes changing blades frequently, cutting away from the body, keeping the free hand clear of the cutting line, wearing cut-resistant gloves, and retracting or sheathing the blade when moving around the roof. Used blades should go into a closed container rather than being left on the roof or in debris. In hot weather, asphalt products are softer and cut more easily; in cold weather they can crack, and some roofers warm shingles before cutting.