What is roof flashing?

What does roof flashing do?

Flashing keeps rain out of the joints where a roof meets a wall or is cut through, and steers that water down the roof and into the gutter; U.S. Department of Energy guides explain it: “The fundamental principle of water management is to shed water by layering materials in such a way that water is directed down, out, and away from the building.” Source: U.S. Department of Energy, Building America Solution Center (Pacific Northwest National Laboratory), read 2026-10-29. “Step and kickout flashing should be installed at all roof-wall intersections to protect the wall and divert rainwater runoff into a gutter.” Source: U.S. Department of Energy, Building America Solution Center (Pacific Northwest National Laboratory), read 2026-10-29. “This flashing diverts rainwater runoff into gutters and protects walls from water intrusion.” Source: U.S. Department of Energy, Building Science Education Solution Center, read 2026-10-29. “Missing flashing can lead to water infiltration and major damage and rot that may be hidden beneath the walls or roof.” Source: U.S. Department of Energy, Building America Solution Center (Pacific Northwest National Laboratory), read 2026-10-29.

How does the Department of Energy describe roof flashing?

Roof flashing is a thin, waterproof material, most often metal, fitted at the weak joints of a roof so rain is sent down and off it. The U.S. Department of Energy's Building America Solution Center describes it this way: “Flashing is a thin, waterproof material, often metal, rubber, or vinyl, used to create a barrier against water intrusion at vulnerable junctions and penetrations in a building's exterior, such as where a roof meets a wall, or around pipes, vents, and windows.” Source: U.S. Department of Energy, Building America Solution Center (Pacific Northwest National Laboratory), read 2026-10-29. “Flashing directs water down and out of a building (Figure 1).” Source: U.S. Department of Energy, Building America Solution Center (Pacific Northwest National Laboratory), read 2026-10-29. “The most elegant expression of the concept of drainage is flashing.” Source: U.S. Department of Energy, Building America Solution Center (Pacific Northwest National Laboratory), read 2026-10-29.

What is roof flashing made of?

Most roof flashing is corrosion-resistant sheet metal such as galvanized steel at least 0.019 inch thick, while some pieces, like kick-out diverters and flashing tapes, are molded plastic or self-adhesive tape: In Minnesota, “Where flashing is of metal, the metal shall be corrosion-resistant with a thickness of not less than 0.019 inch (0.5 mm) (No. 26 galvanized sheet).” Source: State of Minnesota, Office of the Revisor of Statutes (Minnesota Rules, Department of Labor and Industry), read 2026-10-29. “If metal, the flashing should be made of galvanized steel at least 0.019 inches thick (IRC 2015).” Source: U.S. Department of Energy, Building America Solution Center (Pacific Northwest National Laboratory), read 2026-10-29. “Step flashing is often made of corrosion-resistant metal.” Source: U.S. Department of Energy, Building Science Education Solution Center, read 2026-10-29. “Diverters consist of prefabricated seamless, molded plastic pieces or metal with welded seams.” Source: U.S. Department of Energy, Building Science Education Solution Center, read 2026-10-29. “Metal flashing and self-adhesive flashing tapes protect vulnerable building components and help direct water down and out of the building (see Figure).” Source: U.S. Department of Energy, Building America Solution Center (Pacific Northwest National Laboratory), read 2026-10-29.

What are the types of roof flashing?

Flashing is named for where it sits: drip edge at the roof edge, step, continuous and kick-out flashing where a roof meets a wall, and boots around vent pipes; the U.S. Department of Energy lists them: “Look for drip edge flashing along the bottom edge of the roofing, look for step and kick-out flashing where walls meet roofs.” Source: U.S. Department of Energy, Building America Solution Center (Pacific Northwest National Laboratory), read 2026-10-29. “Look for flashing boots around vent pipes and stacks.” Source: U.S. Department of Energy, Building America Solution Center (Pacific Northwest National Laboratory), read 2026-10-29. “Either continuous L-metal flashing or step flashing is used to prevent water intrusion into the wall where a sloped roof intersects a vertical wall.” Source: U.S. Department of Energy, Building America Solution Center (Pacific Northwest National Laboratory), read 2026-10-29. “Step flashing is used with shingle roofs; continuous flashing is used with metal and rubber membrane roofs.” Source: U.S. Department of Energy, Building America Solution Center (Pacific Northwest National Laboratory), read 2026-10-29. “When installing metal or rubber membrane roofs, use continuous flashing rather than pieces of step flashing.” Source: U.S. Department of Energy, Building America Solution Center (Pacific Northwest National Laboratory), read 2026-10-29.

Where is flashing on a roof?

Flashing goes at every place water can get past the roof covering: where the roof meets a wall, where the slope or direction changes, around openings such as vents and chimneys, and along the edges: In Minnesota, “Flashings shall be installed at wall and roof intersections, wherever there is a change in roof slope or direction and around roof openings.” Source: State of Minnesota, Office of the Revisor of Statutes (Minnesota Rules, Department of Labor and Industry), read 2026-10-29. In Minnesota, “A kick-out flashing shall be installed to divert the water away from where the eave of a sloped roof intersects a vertical sidewall.” Source: State of Minnesota, Office of the Revisor of Statutes (Minnesota Rules, Department of Labor and Industry), read 2026-10-29. “Vents, flue stacks, chimneys, sky lights, mounting brackets, etc., are all penetrations through a roof’s water control layer, which is the roof covering together with the roofing felt, synthetic underlayment, or other weather-resistant barrier installed over the roof decking.” Source: U.S. Department of Energy, Building America Solution Center (Pacific Northwest National Laboratory), read 2026-10-29. “Any roof penetrations must be properly flashed to prevent water entry.” Source: U.S. Department of Energy, Building America Solution Center (Pacific Northwest National Laboratory), read 2026-10-29. “Code compliant metal drip edges should be installed at eaves and gables or rakes (applicable codes set the minimum gauge required).” Source: U.S. Department of Energy, Building America Solution Center (Pacific Northwest National Laboratory), read 2026-10-29.

Is roof flashing required by code?

Yes: U.S. Department of Energy guidance says the International Residential Code (IRC) requires step and kick-out flashing, and Minnesota's adopted rule sets when kick-out flashing is needed on existing homes: “Step flashings and kick-out diverters are required in the 2009 and 2012 IRC (R703.8) and 2015 and 2018 IRC (R703.4; R903.2.1).” Source: U.S. Department of Energy, Building America Solution Center (Pacific Northwest National Laboratory), read 2026-10-29. “Where flashing is metal, the metal shall be corrosion resistant with a thickness of not less than 0.019 inches (26-gauge galvanized sheet) (2018 IRC R903.2.1).” Source: U.S. Department of Energy, Building America Solution Center (Pacific Northwest National Laboratory), read 2026-10-29. As printed by Douglas County, Colorado, “IRC Section R905.2.8.3 Sidewall Flashing – Base flashing against a vertical sidewall shall be continuous or step flashing and shall be a minimum of 4” in height and 4” in width and shall direct water away from the vertical sidewall onto the roof and/or into the gutter.” Source: Douglas County, Colorado, Building Division, read 2026-10-29. In Minnesota, “Kick-out flashings shall be required in accordance with Section R903.2.1 when re-siding or simultaneously re-siding and re-roofing existing buildings and structures.” Source: State of Minnesota, Office of the Revisor of Statutes (Minnesota Rules, Department of Labor and Industry), read 2026-10-29. In Minnesota, “Kick-out flashings are not required when only re-roofing existing buildings and structures.” Source: State of Minnesota, Office of the Revisor of Statutes (Minnesota Rules, Department of Labor and Industry), read 2026-10-29.

Does roof flashing go under siding?

Yes: where a roof meets a sided wall, the upright leg of the flashing runs up behind the siding, and the siding stops just above the roof surface: As printed by Douglas County, Colorado, “Where siding is provided on the vertical sidewall the vertical leg of the flashing shall be continuous under the siding.” Source: Douglas County, Colorado, Building Division, read 2026-10-29. “Install house siding over the step flashing, ending at least one inch above the roof surface.” Source: U.S. Department of Energy, Building America Solution Center (Pacific Northwest National Laboratory), read 2026-10-29. “Extend step flashing at least 4 inches up the wall from the roof deck and at least four inches out along the roof deck (IRC 2015) and integrate the flashing with the drainage plane above (for example, overlap house wrap over it).” Source: U.S. Department of Energy, Building America Solution Center (Pacific Northwest National Laboratory), read 2026-10-29. “Flashing should be integrated with roof and wall drainage planes, such as house wrap or building paper, in a shingle fashion where the top layer of the weather-resistant barrier (WRB) or flashing laps over the bottom layer to prevent water draining behind the bottom layer.” Source: U.S. Department of Energy, Building America Solution Center (Pacific Northwest National Laboratory), read 2026-10-29.

Can roof flashing be replaced?

Yes: U.S. Department of Energy guides say new flashing should go in at roof-wall joints when a roof covering is replaced, and it can also be replaced on its own: “When the roof covering is being replaced on an existing roof, new flashing should be installed at roof-wall intersections.” Source: U.S. Department of Energy, Building America Solution Center (Pacific Northwest National Laboratory), read 2026-10-29. “This flashing may also be replaced as a stand-alone retrofit measure or as part of an exterior wall upgrade.” Source: U.S. Department of Energy, Building America Solution Center (Pacific Northwest National Laboratory), read 2026-10-29. “When the roofing on an older home is replaced, take the opportunity to inspect all of the flashing and repair or replace missing, damaged, or poorly installed flashing at all roof penetrations as well as at roof-wall joints and at valleys.” Source: U.S. Department of Energy, Building America Solution Center (Pacific Northwest National Laboratory), read 2026-10-29. “Install new step and kick-out flashing where an existing roof meets an existing wall as part of a roof replacement.” Source: U.S. Department of Energy, Building America Solution Center (Pacific Northwest National Laboratory), read 2026-10-29.

Sources

• Look for Missing Roof and Wall Flashing — U.S. Department of Energy, Building America Solution Center (Pacific Northwest National Laboratory); read 2026-10-29.
• Roof Edge Protection — U.S. Department of Energy, Building America Solution Center (Pacific Northwest National Laboratory); read 2026-10-29.
• Flashing of Penetrations in Existing Roofs — U.S. Department of Energy, Building America Solution Center (Pacific Northwest National Laboratory); read 2026-10-29.
• Flashing of Roof-Wall Intersections in Existing Homes — U.S. Department of Energy, Building America Solution Center (Pacific Northwest National Laboratory); read 2026-10-29.
• Step and Kick-Out Flashing at Roof-Wall Intersections — U.S. Department of Energy, Building America Solution Center (Pacific Northwest National Laboratory); read 2026-10-29.
• Kick-out Flashing at Roof-Wall Intersections — U.S. Department of Energy, Building Science Education Solution Center; read 2026-10-29.
• Step Flashing at Roof-Wall Intersections — U.S. Department of Energy, Building Science Education Solution Center; read 2026-10-29.
• Kick-out Flashing For Re-Roofing Detail (prints IRC Section R905.2.8.3, dated 2/20/2015) — Douglas County, Colorado, Building Division; published 2015-02-20; read 2026-10-29.
• Minnesota Rules part 1309.0903, Section R903, Weather Protection (amends IRC Section R903.2.1), published electronically March 31, 2020 — State of Minnesota, Office of the Revisor of Statutes (Minnesota Rules, Department of Labor and Industry); published 2020-03-31; read 2026-10-29.