Step flashing (roof-to-wall)

Step flashing is a series of overlapping L-shaped metal flashings stepped up a vertical wall at the line where a sloped roof meets the wall, used to seal the junction against water entry. Each individual piece is L-shaped (one leg under the roof tile or sheet, one leg up the wall) and they overlap each other as they climb the slope. Step flashings appear at chimneys, gable walls, parapets, dormer side walls, and roof-to-wall stepped junctions. NCC 2022 Housing Provisions Part 7.3 sets minimum dimensions: 75 mm upturn against the wall, 75 mm lap between adjacent pieces (verified 2026-05-16).

Geometry:

       Wall (chimney, gable, parapet)
       |
       |   ┐─── upper step flashing (laps top of next)
       |  ─┘
       |   ┐
       |  ─┘
       |   ┐ ─ slope of roof
       |  ─┘
       └─────────────  roof surface (tiles or sheet)

Mandatory dimensions (per NCC):

Dimension	Minimum	Reason
Upturn against the wall	75 mm	Holds against wind-driven rain; protects against deflected water
Cover onto the roof	100 mm (typical, more on shallow pitch)	Sheds water from upper to lower piece
Lap between adjacent step pieces	75 mm	Continuous water shed up the slope
Material thickness	0.55 mm or thicker (zincalume or aluminium); 0.45 mm copper minimum	Durability and rigidity

Counter-flashing (the upper cap):

The exposed top edge of the step flashing’s upturn against the wall is never left exposed. It is covered by a counter-flashing that is chased or tucked into a mortar joint, providing the upper water-seal:

Component	Purpose
Step flashing (this)	Catches water from above and sheds it onto the roof below
Counter-flashing	Covers the top edge of the step flashing’s upturn; tucked into the wall

Together they form the full roof-to-wall seal. Step flashing without counter-flashing is incomplete; counter-flashing without step flashing is incomplete.

Materials:

Material	Where appropriate
Zincalume (G300, AM150 coating)	Standard residential, away from coastal exposure
Aluminium	Coastal, where zincalume corrodes; powder-coated to colour
Copper	Heritage and premium residential; develops patina
Lead	Heritage repair only (banned for new work in most states; toxicity)
Stainless 316	Severe marine; expensive

Application sequence (on tiled roof at chimney side wall):

Install the roof tiles up to the wall in the usual sequence.
Place the first (lowest) step flashing at the eave-end. The lower edge sits on the tile below; the upper edge points up the slope.
Tuck the upturn behind the wall counter-flashing (or up the wall if counter-flashing comes later).
Place the next tile course so the lower edge sits over the flashing’s roof leg.
Place the next step flashing so its lower edge laps 75 mm over the previous one, and the cycle continues.
Continue up to the highest tile course.
Install the counter-flashing along the wall, chased into the mortar joint or held by a top-fixed channel, dressed down over the step flashings.

Step vs continuous flashing:

Flashing type	Where it’s used
Step flashing (this)	Where slope changes vertical position with each course (typical pitched roof against wall)
Continuous flashing	Where the wall is parallel to the slope edge (e.g. ridge against wall) and a single long piece works
Saddle flashing	At intersections of multiple slopes

Common defects:

Insufficient upturn: 50 mm against wall, fails wind-driven rain.
Short laps between pieces: 50 mm or less; water gets under at the joint.
Counter-flashing missing or surface-fixed: exposed top edge; water track behind the flashing.
Sealant used in lieu of overlap: sealant works for 5-7 years, then fails; lap is the permanent seal.
Wrong material in coastal sites: zincalume corrodes within 5-10 years near the coast.
Step flashings not lapping over tiles correctly: water tracks down the wall behind the flashing.

Repair:

Step flashing damage is hard to repair without removing the adjacent tiles. Plan replacement at re-roofing (every 25-50 years for tiles) rather than spot-patching. Spot-patches with sealant rarely outlast 5 years.

Also known as: stepped flashing; soaker (UK/heritage); L-flashing series; chimney step flashing; gable step flashing.

Category: Roof.

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