A sturdy roof does more than just keep rain out—it protects your home’s structure and everything inside. Step flashing is a small but vital component where the roof meets vertical surfaces like walls, chimneys, or dormers. In this blog, we’ll explore why step flashing matters, why you should replace it during a reroof, and exactly how to install it correctly.
Why Step Flashing Matters
Step flashing consists of individual L-shaped metal pieces tucked between each shingle and the vertical surface. Its purpose is simple but crucial: it channels water safely down the roof, preventing leaks and water damage along vulnerable junctions.
- Redirects water away from the joint between roof and wall
- Protects framing and sheathing from rot and mold
- Works with shingles to create a watertight barrier
Without properly installed step flashing, even a high-quality shingle job can fail at the edges, leading to costly repairs and interior damage.
Why Replace Step Flashing on a Reroof
When you reroof, you’re not just swapping old shingles for new ones—you’re rebuilding the roof’s defensive system. Reusing damaged or mismatched flashing can undermine the entire project.
- Flashing ages differently than shingles. Old metal can corrode, crack, or warp, creating gaps under new shingles.
- Building codes and best practices evolve. New flashing profiles, materials, and installation standards may offer better performance than what was used originally.
- A full replacement ensures compatibility. Matching new flashing with new underlayment, shingles, and sealants maximizes longevity.
Skipping flashing replacement is like patching a leaky pipe with duct tape—temporary at best and disastrous long-term.
Materials and Tools You’ll Need
- Step flashing pieces (galvanized steel, aluminum, or copper)
- Custom corner flashings for outside corners
- Underlayment (felt or synthetic)
- Roofing nails (non-corrosive)
- Hammer or roofing nailer
- Tin snips
- Roofing cement or appropriate sealant
- Shingles
Step-by-Step Installation Guide
- Inspect and prepare Remove old shingles and flashing. Check wall sheathing and roof deck for rot or damage and repair as needed.
- Lay underlayment Cover the roof deck with felt or synthetic underlayment, extending it a few inches up the wall.
- Install corner flashing At the lowest corner, set a custom outside-corner piece. Fasten it only to the wall—never nail through both roof and wall surfaces.
- Insert first step flashing Slide the vertical leg of the flashing up the wall and the horizontal leg onto the roof deck. Nail just above the bend, into the deck, so the next shingle covers the nail.
- Position the first shingle Overlap the flashing by at least ¾ inch. Nail the shingle normally, keeping fasteners clear of the flashing.
- Alternate flashing and shingles Continue up the slope: each flashing piece overlaps the one below by 2 inches and is covered by the next shingle.
- Seal and finish At the top termination, install head flashing (also called counter-flashing) over the step pieces. Apply roofing cement or a compatible sealant along all edges.
Common Pitfalls and Pro Tips
- Nail placement: avoid driving nails through the vertical leg of step flashing.
- Material mismatch: don’t mix copper and steel—galvanic corrosion can eat through metal quickly.
- Overlap consistency: maintain a uniform 2-inch overlap for each flashing piece.
- Sealant choice: use high-quality, roof-rated sealant that resists UV and temperature swings.
Final Thoughts
Step flashing is a deceptively simple solution to a complex problem. By replacing it during a reroof and installing it correctly, you safeguard your home against leaks, structural damage, and costly repairs. Next time you plan a reroof, remember: quality flashing work is just as important as the shingles.
Want a printable checklist or personalized project plan? Drop a comment, and I’ll craft one for you.