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Step flashing vs counterflashing: what it means on an inspection

Rafter Tie editorial teamUpdated 3 min read

Step flashing is a series of small bent metal pieces, one per shingle course, that seal where a sloping roof meets a wall that rises above it. Counterflashing is a separate cap piece fixed to the wall or chimney that laps over the top edge of the flashing below. Step flashing is woven in, and counterflashing is placed over.

Two drawings: a sloping roof meeting a wall with bent metal pieces stepped up the roof, labeled step flashing, and a chimney through a roof with a base flashing and a cap strip over its top edge, labeled counterflashing
Step flashing is woven into the shingles. Counterflashing caps the flashing from above.
Use this diagram

How to tell them from each other, and check them

  1. Find where the roof meets a wall. Along a sidewall, where the roof slopes up to a wall that rises above it, step flashing goes in. Each piece is bent in an L, laid over a shingle course, and the next course covers its lower portion.
  2. Check the lap. Each step piece goes under the siding or wall covering above and over the shingle below. Water that gets past a shingle lands on the metal and runs down to the next course.
  3. Find the chimney or masonry wall. Here the base flashing sits at the roof and the counterflashing is a second piece set into the masonry or fixed to the wall above, folding down over the base flashing.
  4. Check the order. Counterflashing must lap over the base flashing, never under it, so water falling down the wall lands on the cap and drops onto the base.
  5. Check the attachment. The cap is fixed to the wall, usually in a joint or slot, and the base is fixed to the roof. The two move independently, which is why they are separate pieces.

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Common mix-ups

  • Step flashing versus continuous flashing. With shingles, a single long strip along a sidewall does not let each course lap properly. The step pieces exist for that reason.
  • Counterflashing versus cap flashing. Many people use the two terms for the same piece. The idea is the same: a cover piece that laps over a base piece.
  • Counterflashing versus a kick-out piece. A diverter at the bottom of a sidewall, where a roof ends against a wall, sends water into the gutter. It is a different part.
  • Base flashing versus step flashing. At a chimney, the front and back often use different pieces than the sides, where step flashing is used.

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Roof flashing on the B1

Roof flashing is part of the roof assemblies chapter, Chapter 9 of the IRC, and wall flashing is in Chapter 7. The roof and ceiling area is 14% of the B1 and wall coverings are in the 27% wall area. Expect a roof-to-wall or chimney scenario with a lapping question. Look up the roof flashing sections by name, and confirm their numbers in your edition before you tab them.

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Pair this with flashing, which covers where flashing goes on walls and openings, and roof pitch, which relates steepness to the roof coverings that need it. The IRC chapters guide shows where Chapters 7 and 9 sit, and the IRC terms glossary lists every term page.

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