Window Weep Paths and Drainage Troubleshooting: A Practical Aluminium Façade Guide

A leaking aluminium window is rarely a window that was built to leak. In most investigations the frame, the glass and the gaskets are doing broadly what they were designed to do, and the water is arriving somewhere the design never intended it to go: a sill channel that cannot empty, a weep slot that was sealed during a touch-up, a head flashing lapped the wrong way, or a pressure-equalised cavity that was never allowed to equalise. Drainage is the least visible part of a façade system and the part most easily compromised on site, because every compromise is invisible at handover and only announces itself after the first driving rain. This guide explains how sill drainage and weep paths actually work, why outlets block, what pressure equalisation is meant to achieve, how flashing and sealant decisions help or defeat the system, what to look for during water testing, and where the boundary sits between routine maintenance and a repair that needs a fabricator. It is written for architects, builders, developers, facility managers and owners who need to resolve a leak rather than simply re-seal it.

Why Sill Drainage Decides Whether a Window Performs

Every opening in a façade is a hole in the weather skin, and every window is a machine for managing the water that inevitably reaches that hole. The glass and the outer gaskets are the first defence, but they are not a sealed vessel. Wind-driven rain arrives with enough energy to cling to surfaces, to be driven upward under an overlap, and to be pushed through gaps that are capillary-sized rather than visible. A window that relies only on the outer seal is therefore relying on a perfect gasket for the life of the building, which is not a realistic expectation for a component that moves, expands, contracts and is routinely cleaned and operated.

The industry answer is to accept that some water will pass the outer line and to design a path for it to leave again. That path runs through the sill. The sill is not a decorative bottom rail; it is a collection tray, a slope, a set of outlets and a pressure boundary, all formed in one extrusion. When it works, water that enters the frame collects at the lowest point and drains outward without ever reaching the interior. When it fails, the same water finds the line of least resistance, which is usually the interior sill, the wall cavity, or the floor structure below.

The Sill as a Collection and Discharge System

A drained aluminium sill typically combines several functions in a single profile. The outer face carries the fixed or sliding sash and presents an upstand that limits direct entry of water. Behind that upstand there is a channel with a floor that falls towards the exterior. The channel terminates at the outer leg, where openings are formed at the lowest point so that water can leave. The glazing rebate sits above or behind the channel, separated by a raised section that is slotted so that water trapped behind the glass can fall into the channel rather than sit against the glazing gasket. Corner joints and end caps close the hollow sections so that water cannot migrate sideways into the wall.

Each of those elements is doing a separate job, and each can fail independently. A sill can be perfectly formed and still fail because the channel floor is blocked by construction debris. It can be correctly slotted and still fail because the slots were painted over. It can drain freely and still fail because the outer leg sits below the level of the adjacent paving, so the outlet discharges into standing water. Diagnosis therefore has to establish which part of the sequence is broken, not simply that water is appearing inside.

Why Water Reaches the Sill at All

Water arrives in the sill by several routes. It can pass the outer gasket under wind pressure and run down the face of the glass into the rebate. It can enter the sash track of a sliding window and pass through the track drainage slots into the sill cell. It can be driven through the joints between frame sections. It can come from above, running down the wall or the head flashing and entering the frame at the head or jambs. It can also come from the wall itself, where a defective flashing or a saturated cavity discharges into the back of the frame.

Distinguishing these routes matters because they point to different trades. Water entering at the head and appearing on the sill is not a sill drainage fault at all, and no amount of weep-slot cleaning will fix it. A useful rule for any investigation is to trace the water backwards from where it appears, asking at every joint whether the water could have arrived there from a higher point. The sill is often the place where a problem becomes visible, not the place where it begins.

The Anatomy of a Weep Path

The term weep path describes the complete route water takes from the point where it enters the frame to the point where it leaves the building envelope. It is a path, not a hole. A window can have every weep slot open and still have no functioning weep path, because a path requires continuity of slope, continuity of opening, and a pressure condition that allows water to move outward rather than inward.

Slots, Baffles and Flap Valves

Weep slots are the visible part of the system: openings formed through the outer leg of the sill at the low point of the channel. Their size and position are set by the system design, and they are usually repeated along the length of the sill so that a single blockage does not disable the whole outlet. Many systems fit a baffle, hood or flap behind the slot. The baffle has two jobs: it reduces the direct impact of wind-driven rain on the opening, and it discourages insects and debris from entering. A flap valve does the same work dynamically, closing against wind pressure and opening under the weight of water.

These small components are a frequent source of trouble precisely because they are small. A flap that has been painted shut will not open. A baffle that has been fitted backwards will deflect water inward rather than outward. A hood that has been dislodged during cleaning leaves an open hole that admits both water and debris. When a drainage complaint is investigated, the condition and orientation of these fittings should be checked before anything more invasive is considered.

Rebate Drainage and Internal Continuity

Behind the visible slot there is a second, less obvious path. Water that passes the glazing gasket sits in the rebate, on the setting blocks, against the edge seal of the glass. If that pocket has no outlet, it becomes a permanent reservoir and eventually finds its way past the inner gasket or into the frame section. Rebate drainage slots or notches allow that water to fall into the sill channel. They are easily blocked by sealant during glazing, by swarf from site drilling, or by the bedding compound used to seat the glass.

Continuity also has to be considered in three dimensions. A sill channel that falls to the front but is interrupted by a fixing screw, a packer or a bead of sealant no longer drains as a single plane; it drains as a series of ponds, and only the pond nearest an outlet will empty. Hollow frame sections must be closed at their ends, or water will travel along the section and emerge somewhere unrelated, often inside the wall. Good drainage design is therefore less about the size of the outlet than about the absence of traps, dams and dead ends between the water and the outside.

Blocked Outlets: The Most Common Failure

If a drainage complaint is traced to its origin, the cause is frequently something that entered the slot after installation rather than a defect in the window. The list is short, repetitive, and almost entirely preventable.

Sealant. A bead run along the sill to “finish” the junction, a smear used to tidy a corner, or a full seal applied to stop a draught can close every outlet along an elevation. This is the single most common cause of a sill that holds water.
Paint and powder coating. Site painting or touch-up can bridge a slot or glue a flap shut. The film is thin enough to be overlooked and strong enough to seal the opening.
Render, mortar and tile adhesive. Masonry and cladding trades working after the windows are installed routinely drop material into sills and weep holes. Mortar droppings inside a masonry veneer cavity can also block the weepholes that the window drainage relies on.
Construction debris. Swarf, screws, offcuts, tape, plastic wrapping and foam fragments collect at the low point of the channel, which is exactly where the outlet is.
Biological growth and silt. In sheltered or coastal locations, dust, pollen, salt and organic matter accumulate in the channel and in the slot, progressively reducing the opening.
Later site works. Decking, paving, planter boxes, render and signage installed after handover can raise external levels above the outlet or physically cover it.

Reading the Symptoms

A blocked outlet does not always produce an obvious puddle. More often it produces a pattern. Water appearing on the internal sill after rain from a particular direction, staining or efflorescence at the frame-to-sill junction, paint blistering at the bottom of the reveal, a damp patch on the floor below, or a musty smell in a carpeted room are all consistent with a sill that is retaining water. Water that appears only during high wind, and disappears when the wind drops, points instead towards a pressure or venting problem rather than a simple blockage.

A simple diagnostic is to look at the sill during rain, from outside where it is safe to do so, and observe whether water is discharging from the outlets. If the channel is full and nothing is leaving, the path is blocked. If the channel is empty and water is still appearing inside, the water is bypassing the sill entirely through a joint, a flashing defect or the wall. That single observation separates two very different repair scopes.

Pressure Equalisation and Why Gravity Is Not Enough

Drainage is often described as though water simply falls out of a window. In reality, water leaves only when the pressure at the outlet is lower than the pressure pushing it from behind. Wind changes that balance. A façade under positive wind pressure experiences a higher pressure on its outer face than inside the building, and that difference is what drives water through gaps. A drained and vented window manages this by equalising pressure across the parts of the assembly that are meant to be exposed to weather.

The Rain Screen Principle in a Window Frame

The principle is straightforward. The outer skin, which is the sash, the glazing and the outer gaskets, takes the impact of the rain and sheds most of it. Behind that skin is a cavity, drained at the bottom and vented to the outside. Because the cavity is connected to the outside air, wind pressure acts on both sides of the outer skin, and the pressure difference across the skin is small. The inner line, which is the seal between the frame and the interior, is protected because there is little pressure to drive water across it. Any water that does pass the outer skin falls into the cavity and drains out through the outlets.

The system depends entirely on the cavity being both drained and vented. Seal the vents and the cavity stops tracking the outside pressure; the assembly then behaves like a sealed box with a small amount of water inside it. Seal the drains and the cavity fills. Either mistake converts a pressure-equalised window into a window that relies on a perfect outer gasket, which is precisely the condition the design was trying to avoid.

Why Equalisation Is Never Perfect

Equalisation is a process, not a state. Vents have finite area, cavities have volume, and gusting wind changes pressure faster than a cavity can respond. The result is that a small residual pressure difference always exists across the inner line, which is why the inner seal still matters and why the outer gaskets still matter. The design intent is to reduce the driving pressure to a level the inner seal can tolerate, not to eliminate it. This is also why a window that performs well in a laboratory test can still leak on a tall building corner where gust pressures and façade pressures combine in ways the test did not represent.

For the person troubleshooting a leak, the practical implication is that “the water is being sucked in” is a meaningful observation. Water drawn inward, particularly at a joint or under a gasket, suggests a pressure imbalance rather than a blocked drain. Common causes include sealed vent paths, a missing or displaced baffle, blocked or oversized openings that allow direct wind entry, an internal lining or seal that has been made airtight while the outer cavity was also sealed, and pressure differences created by mechanical systems or by a building that is much tighter than its façade detailing assumes.

Flashing and the Wall-to-Window Interface

Most water that enters a building around a window never touches the window’s drainage system at all. It enters at the interface between the frame and the wall, and the flashing is the component responsible for managing it. A window can be perfectly manufactured, correctly installed and properly drained, and still leak if the flashing above, below or beside it is wrong.

Head Flashings

The head flashing is the roof over the window. It collects water running down the wall above the opening and discharges it to the outside, clear of the frame. To do that it needs an upstand against the wall, a fall towards the exterior, a drip edge that throws water clear of the wall face below, and end dams or turned-up ends so that water cannot run off the ends and into the jamb. It must also be lapped correctly with the wall cladding and with any building wrap or cavity membrane, in shingle fashion, with the upper layer over the lower.

Head flashing defects are easy to introduce and hard to see. A fall that is too shallow, a drip edge that sits tight against the frame head, a flashing that stops short of the jamb, or a membrane that is dressed over the flashing instead of behind it will all produce water at the head during wind-driven rain. That water then runs down inside the frame or the wall and appears at the sill, where it is misdiagnosed as a drainage fault.

Sill and Jamb Flashings

The sill flashing sits under the frame and performs the same job in the opposite direction: it collects any water that reaches the base of the opening and discharges it outward, over the cladding or into a drained cavity. It needs a slope, a drip, an upstand at the back and turned-up ends. Where the window sits in a masonry veneer, the flashing must be integrated with the cavity and with the weepholes that drain the veneer itself, and those weepholes must remain open.

Jamb flashings are often omitted in speculative work because the jamb is assumed to be protected by the frame and the sealant. That assumption holds only until the sealant ages or the frame moves. A jamb flashing turned into the sill flashing and lapped behind the cladding gives water a path back to the outside instead of into the wall cavity.

Where Flashing and Drainage Meet

The critical detail is the junction between the window’s own drainage outlet and the flashing beneath it. Water leaving the sill must be able to fall onto the flashing and run away. If the outlet is set below the top of an upstand, if the flashing is dressed up over the outlet, or if the gap between frame and flashing is filled with sealant, the window drains into a closed tray. The detail works only when the outlet is above the drainage plane of the flashing and the water has an unobstructed route from one to the other.

Sealant Mistakes That Trap Water

Sealant is the most overused material on a façade. It is applied to solve problems that belong to flashing, gaskets, clearances or sequencing, and in doing so it frequently creates the leak it was meant to stop. The mistakes below account for a large share of drainage failures on completed buildings.

Sealing the Outlets

The first and most damaging mistake is sealing the weep slots themselves. It is usually done with good intentions: to stop a draught, to keep insects out, to tidy a visible opening, or to address a complaint about water on the sill. The result is a sill that fills and then overflows inward. Any instruction to seal a sill, and any maintenance procedure that involves applying sealant along the bottom of a window, should be checked against the system’s drainage design before work begins.

Sealing the Wrong Face

The second mistake is sealing the outer face while leaving the inner face open, or sealing both. A drained window expects the outer skin to shed most water and the inner line to be the air and water barrier. Sealant applied over the outer joints can trap water in the cavity with no way out; sealant applied over both faces turns the cavity into a container. The correct approach is to seal the line the system nominates, and to leave the drainage and venting paths exactly as the fabricator intended.

Bridging Movement and Rebate Details

Sealant also causes problems when it is used where a gasket, a backer rod or a drained joint should be. A bead applied with adhesion to three faces has nowhere to stretch when the frame moves, so it tears or debonds, and the failure creates a concealed channel. Sealant applied over the glazing rebate drainage slots during a re-glaze blocks the secondary path. Sealant applied to a damp, dusty or contaminated surface may look continuous but will not bond, and water will pass behind it. Sealant chosen for the wrong substrate or movement capability may fail within a season. None of these failures look like failures at the time of application, which is why records of what was applied, where and by whom are so valuable later.

Sealant Used as a Substitute for Flashing

The most consequential error is using sealant to correct a flashing defect. A bead across a poorly lapped head flashing, a mastic fillet where a sill flashing should turn up, or a sealant bridge over a gap between cladding and frame will hold for a while and then fail, usually at the point where movement is greatest. When it fails, the water reaches the same defective detail and the repair is now more difficult because the evidence has been covered. Sealant is a jointing material, not a waterproofing layer, and treating it as one moves the failure forward in time rather than removing it.

Water Testing Observations

Water testing is how a façade’s drainage behaviour is verified, and it is also one of the most misunderstood parts of the process. A test is only meaningful if the method, the specimen and the acceptance criteria are agreed in advance, and if the observations are recorded in enough detail to be useful when a problem appears later.

Laboratory Testing to AS 4284

AS 4284 sets out methods for determining the performance of windows, including water tightness under a pressure differential. A specimen is installed in a test chamber and subjected to a water spray on the external face while a controlled pressure difference is applied, so that the assembly experiences conditions that represent wind-driven rain. Observations are made on the internal face for the appearance and location of water penetration. Systems in the Meichen range are tested to this method and achieve water tightness up to 960 Pa under AS 4284, which is a statement about the tested configuration and the test conditions, not a prediction for every installation.

What the test reveals is where water first appears and whether the assembly’s drainage and venting details behave as intended. A specimen that passes has demonstrated that, at the applied pressure and for the duration of the test, water did not reach the internal face in a way that exceeded the criteria. It has not demonstrated that the sill channel will still be clear after a decade of site debris, or that the flashing on a particular building was installed correctly.

Site Water Testing

Site testing is a different instrument. A controlled hose test on a completed opening can confirm that water applied to a specific area appears or does not appear inside, and it is valuable for isolating a defect at a head, jamb, sill or corner. It cannot reproduce the pressure differential of a laboratory test, it is difficult to standardise between operators, and it can force water into places it would not reach under natural rain. Used with those limits understood, it is a useful diagnostic; used as a substitute for a laboratory performance test, it is misleading.

Good site testing is staged. The head is tested first, then the jambs, then the sill, with observation inside after each stage and a pause between stages so that the path of any water can be identified. The water is applied at a controlled rate from a sensible distance, not blasted at sealant joints with a high-pressure nozzle, which can damage the very components being assessed. The interior is watched at the sill, the reveal, the frame joints and the wall below, and photographs are taken before, during and after.

What to Record

A test record should identify the opening, the elevation, the system and the glazing, the method used, the equipment, the duration, the conditions, the acceptance criteria and the observations. Observations should describe where water first appeared, how long it took, whether it stopped when the water was removed, and what path it followed. “Leak at sill” is not an observation; “water appeared at the internal sill-to-reveal junction on the left-hand side after water was applied to the head for several minutes, and continued after application stopped” is. The second version tells an investigator that the defect is above the sill and probably at the head flashing or the jamb, which changes the repair entirely.

Interpreting Results Honestly

Two cautions are worth stating. First, a passed test does not prove that a drainage path is clear; water may never have reached the depth needed to test the outlet. Second, a failed test does not always mean the window is defective. Water appearing inside during a test may originate at a flashing, a wall membrane or an adjacent trade’s work. The purpose of testing is to locate the defect, not to allocate blame, and the most useful outcome is a recorded observation that points to a specific detail.

Standards and the Compliance Framework

In Australia, the National Construction Code (NCC) sets the performance requirements that a building must satisfy, and the Australian Building Codes Board (ABCB) administers the code and its referenced documents. For windows and doors, compliance is commonly demonstrated through a product that has been tested and certified to the relevant standards and installed in accordance with the manufacturer’s instructions and the project documentation. The standards that matter in a drainage investigation are the ones that define the product’s performance, the method by which that performance was measured, the way the glass was selected, and the way the assembly was installed.

AS 2047 is the product standard for windows and doors, and it is the reference against which performance characteristics are declared. AS 4284 provides the test methods used to establish those characteristics, including water tightness under pressure. AS 4666 addresses installation, and is the reference that links a tested product to a building that performs as tested. AS 1288 governs glass in buildings, covering the selection of glass type and thickness for the application and the safety requirements that apply. For New Zealand projects, SNZ TS 4211:2022 and SNZ 4223 provide the corresponding framework, and a product certified for one market is not automatically certified for the other.

Certification is specific. It applies to a system, a configuration and a set of components, and it does not automatically extend to a different glazing make-up, a different size, a different hardware set or a different installation condition. Meichen holds certification for 43 product series in Australia and 13 product lines in New Zealand, and the relevant certificate and test report should be checked whenever a project departs from a standard configuration. The practical point for a drainage investigation is that a change made on site, whether to the glazing, the sealant or the flashing, may take the installation outside the tested arrangement, and that this should be recorded rather than assumed away.

Standards are also revised. Any project specification should reference the editions that apply at the time of the contract, and any compliance statement should be read against those editions rather than a summary. Where a project adopts a performance solution rather than a deemed-to-satisfy route, the drainage and weatherproofing strategy should be documented as part of that solution, because the evidence required to support it is different.

Maintenance and Inspection

Drainage systems fail slowly and then suddenly. The slow phase is the accumulation of silt, salt, pollen and debris in a channel that nobody looks at. The sudden phase is the first storm after the outlet closes. A maintenance routine that addresses the sill, the outlets and the seals before they fail is far cheaper than a repair that follows water damage to linings, floors and cabinetry.

Cleaning should begin with the outlets and the channel. Debris is removed by hand or with a soft brush, and the slot is checked for continuity by observing whether water drains freely when the channel is gently wetted. Flap valves and baffles are checked for free movement and correct orientation. Tracks and rollers on sliding windows are cleaned, because a track full of grit both impedes operation and reduces the capacity of the track drainage. Gaskets are checked for continuity, compression and perishing, and sealant joints are checked for adhesion, cracking and separation from the substrate.

External conditions deserve equal attention. Weep holes in masonry veneer must remain open and aligned with the window outlets. Mulch, soil, paving, decking and planter boxes must sit below the drainage level. Render and paint must not bridge an opening. Pressure washing should never be directed into a weep slot or a vent, because the same pressure that removes dirt will drive water past seals that are otherwise sound.

The interval between inspections should be set by exposure and by what the inspections find, not by a fixed calendar assumption. A sheltered inland elevation accumulates debris at a different rate from an exposed coastal one, and a building with trees, construction activity or prevailing wind-driven rain will need more frequent attention. Start with a short interval after handover, inspect after significant wind and rain events, and extend the interval only where the records show that the condition is stable.

Repair Boundaries: What Can Be Fixed and What Cannot

Not every drainage problem belongs to the same trade, and misallocating the repair is one of the main reasons leaks recur. A useful way to think about it is to separate cleaning and adjustment, component replacement, glazing work, fabrication, and building envelope work.

Cleaning and adjustment covers blocked outlets, debris in channels and tracks, displaced baffles, stiff flaps and minor hardware adjustment. This is routine service work and should be within the capability of a competent maintenance team using the system’s own components.
Component replacement covers perished gaskets, damaged flaps, worn rollers and failed sealant joints. It requires the correct parts for the system; generic substitutes can change the drainage and venting behaviour of the assembly.
Glazing work covers re-glazing, replacement of a cracked or failed unit, and restoration of rebate drainage. It should be done by a glazier working to AS 1288 and to the system’s glazing instructions, because the rebate drainage and the setting method are part of the window’s water management.
Fabrication covers replacement of a sash, a sill section, a mullion or a complete frame, and any change to the drainage details of the profile. This belongs with the fabricator or supplier, because it affects the tested configuration.
Building envelope work covers flashing, wall membranes, cavity drainage, cladding laps and the interface between the window and the structure. This belongs with the builder or waterproofer, not the window supplier, and no amount of window repair will correct it.

The boundary is often blurred by the location of the symptom. Water on the internal sill looks like a window problem, but if the head flashing is defective the window is the messenger rather than the cause. A thorough investigation therefore establishes the path before the scope is agreed, and the repair is assigned to whoever owns the defective element. Where the cause is uncertain, an isolation test that separately wets the head, the jambs and the sill will usually resolve it faster than a general re-seal.

There is also a boundary in time. A repair that restores drainage is not the same as a repair that restores the assembly to its tested condition. If a section has been replaced with a different profile, if the glazing has been changed, or if the sealant regime has been altered, the installation may no longer match the certification. That does not necessarily make it unsafe, but it should be documented and reviewed with the supplier so that the project’s compliance position remains defensible.

Installation Records That Make Troubleshooting Possible

The difference between a leak that is resolved in an afternoon and one that consumes months usually comes down to records. A drainage investigation asks specific questions: which system was installed, which glazing, which sealant, which flashing detail, in what sequence, and what was covered up before handover. If those answers exist, the investigation narrows quickly. If they do not, the building has to be opened up to find out.

A useful installation record includes the window schedule and the system series for each opening, the profile and glazing specification, the hardware set, the sealant type and the joints it was applied to, the flashing details and lap sequence, the packers and fixings used, the treatment of frame ends and corner joints, and photographs of the drainage details before the wall or lining was closed. Test records, inspection and test plan hold points, and as-built markups should sit alongside them, as should any site instruction that changed a detail from the documented design.

These records serve the installer as much as the owner. They demonstrate that the work followed the manufacturer’s instructions and the project documentation, which is the position any party will need if a dispute arises. They also make maintenance possible, because a technician arriving years later can identify the system, order the correct baffle or gasket, and know where the outlets are before touching anything. In the absence of records, the safest assumption is that the assembly is not standard, and the investigation should proceed accordingly.

Frequently Asked Questions

Why does water appear on the inside sill only during strong wind?

Water that appears only under wind loading, and clears when the wind drops, usually points to a pressure problem rather than a simple blockage. The likely causes are blocked vent paths, a displaced or missing baffle, a cavity that has been sealed so that it can no longer track outside pressure, or a joint that opens under movement. Check that the weep slots and vents are open and that the baffles are correctly fitted before assuming the gaskets have failed.

Can I seal the weep slots to stop draughts?

No. Sealing the slots removes the only outlet for water that enters the frame, and the result is a sill that fills and overflows inward. If draughts are the concern, the correct response is to investigate the inner seal, the gaskets and the hardware, not to close the drainage path.

How do I tell whether the window or the flashing is leaking?

Isolate the elements. Apply water to the head only and observe inside, then to each jamb, then to the sill. Water that appears when only the head is wetted has not come through the sill drainage, whatever the location of the visible damp. A staged test of this kind is usually more informative than a single overall spray.

Is a site hose test as good as a laboratory test?

No. A laboratory test to AS 4284 applies a controlled pressure difference as well as water, so it represents wind-driven rain in a repeatable way. A hose test is a diagnostic tool for locating a defect on a specific opening. It is useful, but it does not establish the performance of the product and should not be presented as if it does.

Water is appearing at the head of the window. Is that a drainage problem?

Usually not. Water at the head points to the head flashing, the wall membrane, the cladding laps or the junction between the frame and the wall above. The sill may still be functioning correctly, and cleaning it will not stop the leak.

Do I need to remove the window to clear a blocked weep path?

In most cases no. Blocked slots, silted channels, displaced baffles and debris in tracks can be cleared from outside with hand tools and a soft brush. Removal becomes necessary when the blockage is behind the frame, when the rebate drainage has been sealed during glazing, or when a section has been damaged.

How often should weep paths be cleaned?

Base the interval on exposure rather than a fixed number. Coastal, exposed and tree-lined sites accumulate debris faster than sheltered inland ones, and buildings near construction or earthworks need more frequent checks. Inspect after significant wind and rain events, and let the recorded condition guide any extension of the interval.

Does a certified window guarantee that it will not leak?

No. Certification confirms that a tested configuration met the relevant performance criteria under the conditions of the test. It does not confirm that the flashing was installed correctly, that the drainage path was left clear, that the wall is weathertight, or that the assembly has been maintained. Those are separate responsibilities, and they are the ones most often responsible when a certified product leaks.

Can sealant fix a leaking corner?

Sealant can close a small joint temporarily, but a leaking corner is usually a symptom of a missing flashing lap, a gap in a gasket or a drainage path that has been bridged. Sealing over it conceals the cause and often traps water where it does more damage. The corner should be opened, the detail inspected and the defect corrected before any sealant is applied.

What records should I ask for at handover?

Ask for the window schedule with system series, glazing and hardware specifications, the sealant schedule, the flashing details and lap sequence, photographs of the drainage details before closing, test and inspection records, and the maintenance instructions. These documents are the baseline for every later investigation, and they are much harder to reconstruct once the building is occupied.

Conclusion

Window drainage is a system of small, unglamorous decisions that only become visible when they are wrong. The sill has to collect water and let it go; the weep path has to be continuous from the rebate to the outside; the cavity has to breathe so that pressure does not push water inward; the flashing has to take water away from the opening before the window ever sees it; and the sealant has to seal the line it was meant to seal without closing the lines that must stay open. When a leak appears, the useful question is not where the water is visible but where it entered, and the answer is found by tracing the path rather than by adding more sealant.

Testing, records and maintenance are what keep that system honest. A test to AS 4284 tells a project what a configuration can do under controlled conditions, with tested systems reaching up to 960 Pa. A complete installation record tells an investigator what was actually built. A maintenance routine that clears the outlets and checks the seals keeps the path open between inspections. Together they turn a leak from a matter of opinion into a matter of evidence, and they allow the repair to be aimed at the defect rather than at the symptom.