How to Install Step Flashing On Your Roof

Installing step flashing correctly is crucial for preventing leaks and protecting your roof. With some basic skills and the right materials, you can add step flashing to your roof relatively easily. Here is a comprehensive guide on how to install step flashing properly.

What is Step Flashing?

Step flashing refers to small pieces of metal flashing installed along the roof planes where they intersect with walls or chimneys. The flashing is applied in ‘steps’, with each piece overlapping the piece below it to create a water-tight seal.

Step flashing provides a continuous path for water to run down over the roofing material without seeping underneath. It prevents water from getting behind the siding, causing rot and mold. It is commonly used when installing asphalt shingles but can also be used with other roofing materials.

Benefits of Step Flashing

  • Creates a watertight seal along roof-wall intersections.
  • Prevents water intrusion and damage to roof decking and wall structures.
  • Provides greater protection compared to larger single pieces of flashing.
  • Allows for expansion and contraction of roofing materials.
  • More aesthetically pleasing than large metal flashings.
  • Long-lasting when installed correctly.

When to Install Step Flashing

Step flashing should be installed any time a roof intersects with a vertical wall, dormer, chimney, etc. Common applications include:

  • Along the sidewalls of homes where asphalt shingles meet siding.
  • Around chimneys and skylights.
  • At dormer walls and roof-to-wall connections.
  • Wherever a change in roof direction occurs.

Step flashing is applied after roofing felt or underlayment but before shingles. For re-roofing projects, old step flashing should be removed before installing new flashing.

Choosing Step Flashing Materials

Step flashing is commonly made from galvanized steel, copper, or aluminum. Galvanized steel is the most economical option. Copper and aluminum are longer-lasting but more expensive.

The material should match or complement the color of the roofing. It should also be compatible with the type of roofing material to avoid corrosion or other failures.

The flashing pieces should be angled or bent to match the roof slope. Rectangular pieces 4-6 inches wide work for most applications.

How to Install Step Flashing on a Roof

Installing step flashing correctly takes some skill. Here are the basic steps:

Tools and Materials Needed

  • Metal step flashing pieces
  • Roofing cement/sealant
  • Roofing nails
  • Tin snips
  • Utility knife
  • Hammer
    -Tape measure
  • Level

Step 1 – Measure and Cut the Flashing

  • Measure the length of the roof-wall intersection needing flashing.
  • Cut pieces to 4-6 inches wide and the measured length.
  • Cut upper corners of each piece at 45 degree angles. This helps overlap the pieces.

Step 2 – Lift Bottom Edge of Siding (If Needed)

  • For roof-wall flashing, lift bottom edge of siding enough to slip flashing underneath.
  • Do not lift more than 2 inches to avoid revealing unpainted siding.

Step 3 – Install Roofing Felt Extending Over Wall

  • Run roofing felt or ice & water shield over roof edge at least 2-4 inches down the wall.
  • This provides an extra water barrier beneath the flashing.

Step 4 – Install First Flashing Piece

  • Place first piece snugly along wall and parallel with roof edge.
  • Ensure piece extends 1-2 inches over roofing felt.
  • Nail top corners in place, nailing into roof decking.

Step 5 – Embed in Roofing Cement

  • Apply a thick layer of roofing cement along top edge on back side.
  • This helps create a watertight seal.

Step 6 – Install Each Overlapping Piece

  • Working up the roof, install each piece 2-3 inches higher than previous piece along the wall.
  • Remove any cement squeeze-out between pieces.
  • Nail through flashing at corners, angling nails to avoid nailing through overlapping pieces.
  • Embed each piece in roofing cement along the top back edge.

Step 7 – Install Shingles Over Flashing

  • Once all pieces are nailed in place, install shingles over the step flashing.
  • The front lip should overlap bottom edge of each shingle.

Step 8 – Seal Top Edge

  • Apply roofing cement along top edge where flashing meets wall.
  • This seals top edge and edge of siding.

Step 9 – Trim Shingles Around Flashing

  • Trim shingles flush with the vertical flashing using a utility knife.

When done correctly, the step flashing should provide an effective, watertight seal along the roof-wall intersection. Be sure to inspect regularly and make repairs as needed. Contact a professional roofer if uncertain about proper installation. With the right techniques, you can avoid leaks and costly damage by installing step flashing on your roof.

Tips for Proper Step Flashing Installation

  • Clean surfaces thoroughly before applying flashing or sealant.
  • Avoid nailing through overlapping sections.
  • Use roofing cement generously, creating full coverage.
  • Lap individual pieces at least 2 inches.
  • Firmly press flashing into sealant to ensure good adhesion.
  • Consider painting flashing to match roof color.
  • Take precautions when working on taller roofs.
  • Hire a pro if unfamiliar or uncomfortable with roof work.

Common Step Flashing Problems

Flashing not lapped correctly – Leaks can occur if flashing pieces are not overlapped far enough. Ensure at least 2-3 inches of overlap with each piece.

Gap at top edge – Any gaps or cracks along the top edge can allow water intrusion. Generous sealant application is key.

Flashing not angled with roof – The flashing must run parallel to the roof slope. Make gentle bends if needed.

Exposed nails – Nails should anchor top corners only without puncturing overlapping sections.

Clogged drainage channels – Debris can clog channels on metal flashings, causing water to pool. Keep them clear.

Loose flashing – Wind or age can loosen flashing. Check for loose pieces and renail as needed.

Corroded metal – Rust, holes and cracking indicate metal flashing has corroded. Replace deteriorated flashing.

Cracked sealant – Dried out or cracked sealant requires new application to maintain the water barrier.


How do I know if my roof needs step flashing?

Your roof needs step flashing anytime it intersects with a vertical wall, dormer, chimney, skylight or other roof-to-wall transition. Check for gaps, cracking or signs of water damage which indicate it’s time to install flashing.

Should step flashing overlap shingles?

Yes, proper installation involves overlapping the front lip or lower edge of the flashing with each shingle course above it while leaving the back end tucked under the upper shingles. This provides a watertight seal.

What is the best way to cut flashing?

Aviation snips provide clean, straight cuts through flashing. Tin snips are optimal but regular metal shears can also work. Avoid torches as the heat can damage the flashing. Mark cut lines first and take it slow.

Should I caulk the top edge of step flashing?

Sealing the top edge where the flashing meets the wall provides an extra barrier against leaks. Use a quality roofing cement or polyurethane sealant and spread it generously along the top back edge before nailing in place.

What type of nails should be used to install step flashing?

Roofing nails are ideal as they have increased durability and large heads to properly anchor the flashing. Nails should be galvanized or stainless steel. Ring shank nails provide the best grip.

Should I paint step flashing for appearance?

Painting step flashing to match your roof color gives a more cohesive, attractive look. Use a high quality exterior metal paint in a color matched to your roof. Allow paint to fully cure before exposing to weather.


Installing step flashing properly is an essential process in roofing and waterproofing. While it may sound complicated, with the right materials and techniques you can correctly add step flashing around roof penetrations. Pay close attention to properly overlapping and sealing each piece while avoiding common mistakes. With some patience and basic roofing skills, you can master the process of installing step flashing on your roof. Be sure to take appropriate safety precautions when working on roofing projects. Contact a professional roofer if you have any concerns or questions.