Flashing
Flashing is a waterproofing strip or sheet at wall and roof junctions to prevent water ingress. Incorrectly lapped flashing is a top cause of water damage claims.
Ask Chalkline about this →Flashing is a strip or sheet of impervious material (typically aluminium, zinc, galvanised steel, or flexible membrane) installed at junctions in the building envelope to prevent water from penetrating behind cladding, into wall cavities, or around window and door openings. It is installed at window heads, jambs, sills, roof-to-wall junctions, penetrations, and any change of plane where water could otherwise track inward.
The fundamental rule for flashing is the shingle principle: upper layers must overlap lower layers so that water is always shed toward the outside. Where this principle is broken (for example, where a flashing laps incorrectly, is omitted at a head, or relies on sealant alone without a physical lap), water ingress typically results. Missing or incorrectly installed window head flashing is one of the most common defects identified in residential construction and a frequent source of warranty claims.
At window openings, flashing works together with the window frame’s own weatherproofing system, backing rod, sealant, and the adjacent wall sarking layer. The ABCB Housing Provisions 2022 Part 8.2 sets out clearance and installation requirements for windows that interact directly with flashing details.
Category: Building envelope / waterproofing
Related
See also
- Sarking, the membrane behind cladding that flashing typically laps over
- NCC, the code that governs weatherproofing requirements for external walls
Last updated: 2026-05-08. Verified: 2026-05-08.