Flashings manage water at every point where the cladding system meets something else - a parapet, a window, a floor slab, a corner, a pipe through the wall. In a rainscreen facade, the outer cladding deflects most rain and a drained cavity handles what gets through. That principle works well across the field of the wall. At junctions, it gets tested. Flashings are what keep the system honest at those transitions.
This guide covers the key junction types, material choices, and membrane detailing for aluminium rainscreen cladding - with specific reference to Valmond & Gibson’s interloQ and element13 systems.
How does water management work in a rainscreen system?
A rainscreen facade has two lines of defence. The outer cladding deflects the bulk of wind-driven rain. Behind it sits a ventilated cavity, typically 25mm or more, backed by a secondary weather-resistant membrane (sarking) on the building structure. Moisture that penetrates the outer skin drains downward through the cavity and exits at the base through weep openings.
Flashings exist at every point where this drainage path is interrupted. Their job is to collect water within the cavity and direct it outward. A flashing that fails or is missing at a single junction can undermine an otherwise well-designed system.
What are the key junction types?
Head flashing - top of wall and parapets
The head flashing prevents water from entering the top of the cavity. Water that gets behind the cladding at the top has the entire height of the wall to travel before reaching a drainage point, finding its way into the structure at any fixing, penetration, or membrane lap along the way.
A head flashing should extend over the top cladding panel and turn down into the cavity, creating a drip edge. At parapets, the flashing integrates with the capping and must direct water outward, not back into the cavity. The connection to the membrane behind must be continuous and sealed.
Sill flashing - base of wall
The sill flashing is the exit point for cavity drainage and prevents water pooling at the base where moisture can wick upward into the structure. It should slope outward and extend beyond the cladding face to form a drip edge.
The base is also a primary ventilation entry point - air drawn in here supports the convection cycle that dries the cavity. The detailing needs to allow both drainage and ventilation without creating an entry point for wind-driven rain. Perforated or slotted flashings achieve this balance.
Window and door head and sill
These are among the most critical junctions on any facade. The interface between the cladding and fenestration is where two different systems meet, often designed and installed by different trades.
At the window head, a flashing collects water draining down the cavity above and directs it out over the window frame with a drip edge, so water falls clear rather than tracking back into the window-to-wall junction.
At the window sill, the flashing collects water from the frame drainage and discharges it outward. The sill flashing should slope outward, turn up at the back to create a dam against the membrane, and extend beyond the cladding face. Sill flashings that are flat or slope inward are a common source of water ingress.
The installation sequence matters - membrane first, then flashing, then cladding. Getting this order wrong means water that reaches the membrane has no clear path outward.
Internal and external corners
A change of plane creates a junction where flashings from two adjacent wall sections must meet. The challenge is continuity - the water management path must be unbroken around the change of direction.
At external corners, flashings should be formed as a single piece around the corner where possible, or lapped with the upstream piece over the downstream piece. Butt joints at corners are a weak point - where pieces meet, the lap should be at least 50mm and sealed.
Internal corners collect water from two converging planes and must be detailed so water channels outward rather than pooling. A formed gutter piece at internal corners is more reliable than sealant alone.
Penetrations - pipes, services, and fixings
Any element passing through the facade interrupts both the cladding and the membrane behind it. The membrane should be cut and dressed around the penetration with generous overlap, sealed with compatible tape or sealant. A collar on the cladding face sheds water away from the penetration, and a small diverter flashing above it directs cavity water around the seal rather than pooling against it.
Fixings through the cladding are also penetrations, though often overlooked. In a rainscreen system, water entering at fixings drains down the cavity and exits at the base. But at junctions, fixings near flashings should be sealed or positioned so they do not compromise the flashing.
Floor level transitions
On multi-storey buildings, floor slabs intersect the facade zone at each level. A horizontal flashing at each floor collects water from the storey above and discharges it through a weep or drip detail at the cladding face, compartmentalising the drainage path rather than relying on a single exit point at the base of a multi-storey cavity.
What materials should flashings be made from?
For aluminium cladding systems, aluminium flashings are the natural choice - non-combustible, durable, and no risk of dissimilar metal corrosion. Stainless steel is also suitable where higher strength is needed. Coated steel (such as Colorbond) is common in general construction but requires care in contact with aluminium - without proper isolation, galvanic corrosion will occur, particularly in coastal or high-humidity environments.
The rule is straightforward: avoid direct contact between dissimilar metals without an isolating barrier. Neoprene, EPDM, or butyl tape between the flashing and the aluminium cladding prevents galvanic corrosion where different metals must meet.
How does the secondary membrane fit in?
The sarking or weather-resistant membrane on the building structure is the second line of defence. If every flashing were to fail, the membrane is what stands between the water and the structure. It needs to be continuous, correctly lapped (upper sheets over lower sheets so water sheds downward), and sealed at all penetrations, corners, and junctions.
Under the NCC, sarking-type materials less than 1mm thick with a Flammability Index of 5 or less are permitted under C2D10(6)(f) within non-combustible wall assemblies. This allows standard building wrap products as the secondary membrane behind non-combustible cladding - but the product must meet the Flammability Index threshold.
The membrane and flashings work together. The membrane provides a continuous waterproof plane; the flashings manage water at transitions and direct it outward. At every junction, the membrane must be dressed to the flashing so there is no path for water to get behind it. Sealant alone at these interfaces is not sufficient for long-term reliability.
How do interloQ and element13 handle junction waterproofing?
interloQ’s interlocking extrusion profile provides inherent weather resistance panel-to-panel - the mechanical interlock manages water at every joint across the field of the wall, tested as an assembly to AS/NZS 4284 at plus/minus 1500Pa SLS. But interloQ panels still terminate at edges. At top and bottom of wall, openings, corners, and penetrations, a flashing manages the transition between the interlocking panel field and whatever it meets.
element13 solid aluminium panels are typically installed with open joints - deliberate, as part of the rainscreen principle. Water entering through open joints drains into the cavity and down to the base flashing. This means the cavity and membrane carry a greater waterproofing burden than in a system with interlocking joints, and flashings at every junction must be detailed with particular care.
Why should you favour mechanical flashings over sealant?
Sealant degrades. UV exposure, thermal cycling, building movement, and ageing all take a toll. A sealant joint that performs well at handover may be compromised within five to ten years.
Mechanical flashings work through geometry, not adhesion - gravity pulls water downward and the flashing directs it outward. A well-formed aluminium flashing has the same service life as the cladding itself.
Sealant still has a role as a secondary seal at flashing laps, membrane interfaces, and around penetrations. But it should supplement a mechanical water management strategy, not replace one. If the only thing between water and the building structure is a line of sealant, the detail needs rethinking.
Where do V&G’s technical details fit in?
Valmond & Gibson provides typical junction details in the technical documentation for interloQ and element13. These cover each junction type and serve as a starting point for project-specific detailing.
Every project is different. The substrate, window system, insulation build-up, structural tolerances, and exposure conditions all influence how junctions should be detailed. The facade engineer is responsible for adapting typical details to the specific conditions and confirming the assembly performs as required.
V&G’s systems have been tested to AS/NZS 4284 at plus/minus 1500Pa SLS, demonstrating weather performance under simulated wind and rain. The junction details on each project must be consistent with the principles that underpin that tested performance.
If you need typical junction details, compliance documentation, or technical support for a specific project, contact the V&G technical team. The right time to resolve a flashing detail is during design - not when the installer is standing on the scaffold looking at a gap.
Related Reading
- Window and Door Integration with Rainscreen Cladding
- Penetrations Through Aluminium Facades: Best Practice
- Ventilated Facade Design: Principles and Performance
- Quality Control During Aluminium Facade Installation
Last updated: 4 April 2026