How to Use a Hook Blade Utility Knife for Shingles and Membranes
Score from the right side, pull toward safe space and change the blade often. The hook keeps the cut on the line and your hand behind the edge.
- Beginner
- Learn in under an hour
- Updated
The short answer
A hook blade knife has a curved, recessed cutting edge that cuts shingles, felt, underlayment and membrane when pulled toward you along a straightedge. Put a sharp hook blade in, support the material on a solid surface, pull toward a safe space with your other hand behind the cut, score and snap shingles, and change blades as soon as they drag. Retract or cap the blade between cuts.
The hook blade is the roofer's knife. It is a short, curved blade with the cutting edge on the inside of the hook, so it cuts on a pull stroke and stays on the line of the cut better than a straight blade does. It cuts asphalt shingles, felt and synthetic underlayment, ice and water shield and roll roofing quickly. Because the hook points away from your hand on a pull cut, it is also the safer blade for cutting on a roof, provided it is used properly.
Nearly every roofer has a story about a knife. Most injuries happen because of a dull blade, a cut made toward the body, or a blade left exposed in a pocket. This guide covers choosing blades, how to cut each material, how to change a blade safely and how to care for the knife. For more on the cuts themselves, see how to cut asphalt shingles and how to install ice and water shield. Membrane cutting is also part of torch-on cap sheet installation.
Tools
- Utility knife that takes hook blades
- Spare hook blades in a dispenser
- Straightedge or shingle cutting guide
- Chalk or marker
- Cut-resistant gloves
- Hard surface such as a cutting board or bundle of shingles
Materials
- Hook blades, carbide if the material is tough
- Shingles, underlayment or membrane to cut
- Blade disposal container
Safety first
- Always cut away from your body and your free hand. Keep the free hand behind the knife, not in front of it, and never hold the material against your thigh while cutting.
- Change the blade as soon as it drags. A dull blade needs more force, and more force means a slip that goes where it should not.
- Retract the blade or fit the guard whenever you put the knife down or carry it, and never leave an exposed blade in a pocket or on the roof.
- Dispose of used blades in a sharps container, a metal tin or a dispenser made for it. Loose blades on a roof or in a bin injure people.
Step by Step
Step 1: Choose the right blade and knife
A hook blade cuts on the pull and is best for shingles and roll goods. A straight blade is better for marking, scoring and delicate trimming. Standard steel blades dull quickly on the mineral granules of asphalt shingles, and carbide-tipped hook blades last many times longer. Choose a knife with a firm blade lock, a comfortable grip and a blade storage compartment.
Check that the blade fits the knife, since hook blades have a different shape and mounting than standard straight blades.
Step 2: Put in a fresh blade correctly
Do the change on a stable surface, not on a slope. Pull the old blade out with pliers if it is hot or stuck, and put it in a sharps container, not in your pocket. Seat the new blade fully in its slot and make sure the lock engages. A loose blade flexes and can snap. Keep your fingers clear of the edge while you change it.
Step 3: Support the material on a solid surface
Cutting into a roof deck dulls the blade and can cut the layer beneath, so cut shingles on a bundle or a board when you can. Keep the material flat and stable, and keep the line of the cut free of your hand. Do not cut in the air or while holding the material against your leg.
Step 4: Mark the line and use a straightedge
A guide such as a shingle cutting square, a drywall square or a straight board keeps the cut straight. Place your free hand on the straightedge well back from the blade's path, so if the knife slips off the edge, it does not meet your hand. For cutting shingles to fit valleys, see how to cut asphalt shingles.
Step 5: Score the material with a steady pull
For asphalt shingles, score through the top surface and the mat, then bend the shingle along the score and snap it, finishing with a cut from the back if needed. For roll goods, use a lighter pull and let the blade do the work. Pressing too hard forces the blade and skids it off the line. Several light passes are safer and cleaner than one heavy one.
Position your body so the blade cannot travel toward your legs if it slips. Stand to the side of the cut, not behind it.
Step 6: Cut membranes and felt without cutting what is underneath
A knife that cuts through ice and water shield can also cut the sheet below it or scratch the deck. Use a light touch, and slide a flat piece of scrap under the line where you can. For single-ply membrane, the cut is often made from the top using a sharp blade and a straightedge, with a fresh blade each time you start a run. On torch-on sheet, keep the knife away from the flame and away from hot asphalt.
Step 7: Retract and stow the knife every time
A knife left on a slope slides off the roof or cuts the next person who reaches for it. Retract the blade every time you put it down. Use a holster or a belt clip with a retracting blade. Hang a tool lanyard from the belt if you work at height.
Step 8: Sharpen, swap and dispose of blades safely
A sharp blade cuts with little pressure. A dull one catches and tears. Swap often, and keep a dispenser on your belt or in your bucket. Collect used blades in a tin or a sharps container and tape it shut when full, so they do not cut anyone handling the garbage.
Hook Blade Versus Straight Blade
A straight blade is more versatile, and is better for marking, trimming and delicate cuts. A hook blade is made for pulling through thick or layered material, keeps to the line, and puts the tip out of the way of your hand. On a roof, where most of the cutting is through shingles, membrane and underlayment, the hook is the standard. Many roofers carry a knife of each type.
Carbide Blades
Carbide-tipped blades cost more, but they hold an edge through many more shingles than a steel blade, and they reduce the number of blade changes. They are harder and can chip if dropped or twisted, so use them for straight pulling cuts and do not use them as a pry bar.
Common Mistakes
- Working with a dull blade. It needs more force and slips off the line.
- Cutting toward the body or the free hand. One slip is a serious cut.
- Holding the material against your leg while you cut it.
- Pocketing an exposed blade. It cuts you or the next person who reaches in.
- Cutting into the deck or the layer below. Dulls the blade and damages the roof.
- Dropping used blades loose on the roof or into a bin.
When to Call a Professional
Cutting shingles and membranes with a hook blade is a skill you can learn on scrap. The place to get help is on cuts that have to be precise, such as around valleys, penetrations and curbs, where a bad cut means replacing material or a leak.
If you have a deep cut, get first aid and medical help at once. Keep pressure on the wound and do not try to keep working.
Fraser Roofing does free roof inspections across the Fraser Valley, from Hope to Abbotsford. See our Roof Replacement service or the towns we cover.
How to Use a Hook Blade Utility Knife: Questions
What is a hook blade used for in roofing?
A hook blade is a curved utility blade that cuts on a pull stroke and stays on the line, used for asphalt shingles, felt, synthetic underlayment, ice and water shield, roll roofing and membrane. The recessed cutting edge and the direction of the pull keep the tip away from your hand. It is the standard roofing knife.
How do you cut shingles with a utility knife?
Lay the shingle flat on a bundle or board, lay a straightedge along the marked line, and pull a hook blade along it in one or two firm passes to score through the top and the mat. Bend the shingle along the score to snap it, and finish with the knife from the back if needed.
How often should you change a utility knife blade?
As soon as it starts to drag, tear or need extra pressure. Asphalt shingles are abrasive, so a steel blade can dull after only a few cuts. Carbide blades last much longer. A sharp blade is safer because it cuts with less force and is less likely to slip.
How do you change a utility knife blade safely?
Retract the blade and open the knife as its manual describes, taking the old blade out with pliers if needed. Drop it in a sharps tin, seat the new blade fully in its slot, and check that the lock engages. Do the change on a stable surface, away from the edge of the roof, with your fingers clear of the edge.
Is a carbide blade better for roofing?
Carbide-tipped hook blades stay sharp far longer than steel through the mineral granules on shingles, which saves blade changes and cuts more safely. They cost more and can chip if twisted or dropped, so use them for straight pull cuts only. Many roofers carry both carbide and steel blades for different jobs.
Related Guides
All Roofing Tools guides|The full How-To Library
This guide is general education. Always follow the product manufacturer's installation instructions, the BC Building Code and WorkSafeBC requirements, which take priority over anything written here.
Want someone to look at your roof?
Kory & Johnny have roofed homes across the Fraser Valley since 2016. Free inspections, honest estimates, no pressure.
604-728-0146Text UsEmailServing Hope, Agassiz, Chilliwack, Rosedale, Abbotsford & the entire Fraser Valley