Quick definition
Thin, water-resistant material, usually metal, installed at joints, intersections and penetrations to direct water away from vulnerable areas of the roof.
Most roof leaks don't start in the middle of a slope. They start where the roof meets something else: a wall, a chimney, a pipe, a valley. Flashing is what keeps water out at those joints.
What is flashing?
Flashing is thin, water-resistant material, usually galvanized steel, aluminum, copper or lead, and sometimes a flexible membrane, installed wherever the roof covering stops or changes direction. It is shaped and layered so water flows over it and away, rather than into the joint.
What does flashing do?
- Seals the joints the roof covering can't seal on its own, such as where a slope meets a wall.
- Directs water away from penetrations like chimneys, vent pipes and skylights.
- Lines valleys, where two slopes send their water into one channel.
- Protects roof edges, as drip edge does at the eaves and rakes.
What are the types of flashing?
| Type | Where it goes |
|---|---|
| Step flashing | Where a sloped roof meets a sidewall or chimney side, one piece per shingle course |
| Counter flashing | On the wall or chimney, overlapping the step or base flashing below it |
| Valley flashing | Along valleys, as open metal or under woven or cut shingles |
| Drip edge | Along eaves and rakes |
| Pipe flashing (pipe boot) | Around plumbing vent pipes |
| Chimney and skylight flashing | Kits or custom-bent pieces around these openings |
| Kickout flashing | At the bottom of a roof-to-wall joint, turning water into the gutter |
What problems happen with flashing?
- Sealant instead of flashing: caulk or roof cement used as the only seal fails as it ages and shrinks.
- Missing kickout flashing: water runs down behind the siding and rots the wall below.
- Reused old flashing: worn or rusted pieces left in place during a re-roof.
- Exposed fasteners: nails through the flashing face become leak points.
- Corrosion: including galvanic corrosion where dissimilar metals touch.
- Cracked pipe boots: rubber seals that crack in sun and heat.
Do building codes cover flashing?
What it means for you
What Flashing means for homeowners
Stains on ceilings near a chimney, skylight or wall usually point to flashing rather than the shingles. On a replacement quote, ask whether flashing will be replaced or reused.
Frequently asked questions
Sources
- International Residential Code, Chapter 9: Roof Assemblies. International Code Council.
Tier 1 authority 路 code - Roof covering manufacturer installation instructions. Technical Reference.
Tier 1 authority 路 manufacturer - The NRCA Roofing Manual: Steep-slope Roof Systems. NRCA.
Tier 2 authority 路 industry - Architectural Sheet Metal Manual. SMACNA.
Tier 2 authority 路 industry