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Flashing: what it means on an inspection

Rafter Tie editorial teamUpdated 3 min read

Flashing is thin, water-resistant material, usually metal, installed where a wall or roof has a joint, an opening or a change of plane. It directs water out and away from the structure. It works by lapping like shingles, with each upper layer over the lower one, so water runs down and out and never behind a joint.

A side section of a wall above a window with blue arrows for water running down, a flashing tucked behind the weather barrier above and turned out over the window head so water is sent out and past the window
Upper layers lap over lower layers so water never runs behind a joint.
Use this diagram

How to check flashing

  1. Find the weak points. Look above windows and doors, at the junction of a roof and a wall, around chimneys and penetrations, where a deck or porch attaches to a wall, and above projecting trim. These are the places the code expects flashing.
  2. Check the lapping order. Water runs down, so the upper piece must lie over the lower one. At a window head, the weather barrier above laps over the flashing, and the flashing laps out over the window. A reverse lap leads water behind the layer.
  3. Check the material. Flashing is corrosion-resistant. Some metals attack each other or react with treated lumber or masonry, so the material has to be compatible with what it touches.
  4. Check the ends. Water finds the end of a flashing. Look for turned-up ends or end dams where the flashing meets an obstruction.
  5. Check the attachment. Fasteners should not be placed where water collects and should not pierce the part that sheds water. Sealant alone is not flashing.

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Common mix-ups

  • Flashing versus caulk. Sealant is a maintenance item that fails over time. Flashing is a mechanical barrier. A joint relying only on caulk is a finding.
  • Flashing versus weather barrier. The weather barrier is the sheet behind the siding. Flashing is the set of pieces that integrate openings and joints with that barrier.
  • Wall flashing versus roof flashing. Walls and roofs have separate sections of the code with different requirements. See the step flashing and counterflashing page for the roof-to-wall joint.
  • Flashing versus drip edge. A drip edge is a metal strip at the eave or rake of a roof. It is related to flashing but is a separate roofing part.

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Flashing on the B1

Exterior wall coverings and flashing are named in the wall construction area, 27% of the B1, and roof flashing falls under the roof assemblies chapter. Expect a location and a question about whether flashing is required, or a lapping order that is right or wrong. Tab the exterior covering flashing section in Chapter 7 and the roof flashing sections in Chapter 9, after confirming the numbers in your edition.

Practice it

Practice finding the sections with the code navigation drill. Then read step flashing versus counterflashing for roof joints, and wall header for the member above the window head you are flashing. The IRC terms glossary links the rest.

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