Aluminium Door Threshold Drainage: Sills, Weeps and Wet-Area Interfaces

Water does not respect the line drawn between a door and a floor. It arrives at a threshold from the sky, from the ground, from a hose, from a wet-area floor being washed down, and from air pressure that pushes it through gaps too small to see. The aluminium threshold is the component expected to manage all of that, and it is usually the smallest item on the drawing.

This article treats threshold drainage as a system rather than a profile. It examines the sill and the sill pan beneath it, the weeps that discharge what collects, the falls that are always determined by the project, the seals, flashings and waterproofing boundaries that surround it, the flooring transitions above it, the glazing it carries, and the maintenance that keeps the whole arrangement working. It also sets out the Australian and New Zealand framework that governs the work. It deliberately quotes no dimensions, falls, costs or performance ratings, because none of those can be responsibly stated without the specific door system, the exposure, the structure and the tested assembly in front of you.

Why a Threshold Is a Drainage Component, Not a Trim

Most door problems are described in the language of hardware: the door sticks, the lock misaligns, the seal perishes. Threshold water problems are described differently, because they appear somewhere else. A damp patch at the base of a wall, a lifted floor finish, a musty smell in a wardrobe, a stain on a ceiling below. By the time the symptom appears, the water has travelled a long way from where it entered.

The Three Water Loads at a Door

The first load is direct rain landing on the threshold and on the lower part of the door leaf. This is the load most people picture, and it is the easiest to shed, because it arrives at a surface that can be shaped to fall outward.

The second load is wind-driven rain. Under pressure, water does not simply fall; it is pushed against the door line horizontally and forced into any path that is not closed. This is why a threshold that performs perfectly in still air can leak in a storm from a particular quarter, and why the performance of a door assembly is always tied to a test pressure rather than to the weather on the day it was installed.

The third load is water that arrives from behind the assembly rather than in front of it: from a wet-area floor, from a balcony that drains toward the door, from a planter bed, from a leaking pipe, or from the cavity of a wall. This load is the one that sill pans, upturns and membrane terminations exist to manage, and it is the one most often missed at design stage because it does not appear in the elevation.

Why Door Thresholds Differ from Window Sills

A window sill sits above a wall and drains to the outside face. A door threshold sits at the level of the floor and must be crossed by people. That single difference changes everything. The threshold cannot simply be built as a sloping shelf with a generous upstand, because the upstand becomes a trip hazard and an access barrier. It cannot be hidden behind a wall, because it is the wall opening. And it must reconcile two floors that are often built by different trades, in different materials, to different tolerances, from opposite sides of the same line.

The result is a detail where the water strategy, the structural support, the access requirement and the finish are all compressed into a narrow band of construction that receives almost no attention in the program. Good threshold drainage is therefore less about a clever profile and more about disciplined coordination.

Sill Pans as a Concept

The sill pan is the idea that a door opening should have a continuous, watertight tray beneath the frame, turned up at the ends, with a defined discharge point. It is a simple concept and it is routinely omitted, because a sill pan is invisible once the door is installed and because its absence only becomes evident under a water load that may not occur for years.

What a Sill Pan Actually Does

A sill pan collects water that has passed the outer line of defence and delivers it back outside. It provides a secondary barrier beneath the frame, so that a failure of the primary seal, a blocked weep or a poorly bedded sill does not admit water into the floor structure or the room below. It also protects the junction between the frame and the substrate from prolonged standing water, which is the condition that degrades sealants and accelerates corrosion at cut edges and fixings.

The pan only works if it is continuous, if it is turned up at both ends and at the back, if it falls toward its discharge point, and if the discharge point is not blocked by the frame, the flashing or the finish. A pan that is continuous but flat holds water. A pan that falls but is not turned up at the ends simply directs water into the wall cavity at each side. A pan with a correctly formed discharge that is then covered by a bead of sealant and a tile has been converted into a container.

Formed, Fabricated and Site-Folded Pans

Sill pans appear in several forms. A proprietary formed pan is purpose-made for the frame width and arrives with the correct upturns and outlet. A fabricated pan is folded from sheet metal, usually with soldered or welded corners, and relies on the fabricator’s workmanship at exactly the points where water concentrates. A site-folded pan uses flexible flashing membrane or a coated metal strip dressed up the jambs and across the sill, and depends almost entirely on the installer’s sequence and care.

All three can work. The choice usually follows the frame type, the substrate, the waterproofing system and whether the door is being installed into new construction or retrofitted into an existing opening. What matters is that the pan is specified as part of the door installation rather than improvised on site, that its material is compatible with the membrane and the sealants it touches, and that its discharge is coordinated with the flashing and the external surface.

Ends, Upturns and the Discharge Point

The two ends of the pan are where most failures occur. Each end must turn up far enough to sit above the highest water level that can reasonably occur in the pan, and must be integrated with the jamb flashing so that water running down the jamb is delivered into the pan rather than behind it. The back of the pan must turn up against the internal face of the frame or the wall, and the front must form a drip or a lap over the flashing below.

The discharge point deserves the same attention. It should be at the low point, it should be sized to pass the debris that will inevitably arrive, and it should be inspectable. Where the pan discharges through a weep in the frame, the two must be aligned. Where it discharges over the outer edge of the sill, the outer edge must be detailed so that water leaves the building rather than tracking back under the frame by capillary action.

Weeps: Purpose, Placement and Path

A weep is an opening that allows water to leave a cavity, a track or a sill. It is a small feature with a large influence on performance, and it is the first thing to be painted over, sealed up, blocked by debris or omitted when a frame is modified on site.

Open Weeps, Baffled Weeps and Cover Caps

An open weep is a simple slot or hole. It drains freely and is easy to inspect, but it also admits wind, insects and, under the wrong conditions, water driven inward by pressure. A baffled weep uses a small hood or flap to allow water out while reducing the direct path for wind and rain. A cover cap or weep cover performs a similar function and improves appearance.

Which is appropriate depends on the exposure and on the tested system. Door and window systems are tested as assemblies, and the weeps are part of the tested configuration. Replacing a baffled weep with an open slot, or deleting weeps because they look untidy, changes the assembly that was tested and documented. That change should be a documented decision, not a site convenience.

Why Weeps Block

Weeps block for ordinary reasons. Paint and powder coat bridge the opening during finishing. Silicone is applied over them by an installer trying to stop a draught. Dust, pollen, leaf litter and insect nests accumulate in the track. A recessed track fills with grit and the drainage path silts up. In each case the water that was designed to leave through the weep has nowhere to go, and it finds the next available path, which is usually inward.

The consequence is a threshold that leaks only after a period of rain, or only when the wind comes from a particular direction, or only in the season when the trees shed. These are the observations that should be recorded at handover and included in the maintenance regime, because they are the earliest available warning that the drainage path is compromised.

Pressure Equalisation and the Drainage Plane

Weeps are often described as though drainage were the whole story. In reality a drained and ventilated assembly works because the cavity behind the outer line is allowed to reach a pressure close to that outside, so that water is not pushed across the assembly by a pressure difference. Weeps and vents together provide that path. Sealing the vents to stop draughts, or filling the cavity with foam to improve thermal performance, can convert a drained assembly into a sealed one that holds water against the inner line.

This is why the drainage plane and the ventilation path must be understood as a single system, and why alterations to a tested door assembly should be reviewed by the supplier rather than decided on site.

Falls and Levels: Always Project-Specific

Every article about drainage eventually proposes a fall. This one will not, because a fall is a design outcome, not a default. It depends on the area being drained, the surface material, the frequency and intensity of rainfall, the wind exposure, the consequences of ponding, the structural set-down available, and the requirements of the membrane or paving system being used.

Why a Nominal Fall Is Not Enough

A fall stated on a drawing is a design intent. A fall achieved on site is a construction result. Between the two sit the tolerances of the slab, the screed, the topping and the finish, plus the reality that a tiler working to a small fall over a large area has very little margin for error. Where the design fall is modest, the construction tolerance can consume it entirely, and the result is a surface that is nominally drained but locally flat or reversed.

The correct approach is to design the fall with the construction tolerance in mind, to show the fall on the drawing with a direction arrow and a stated intent, to require the fall to be verified before the finish is laid, and to provide a secondary path in the form of a sill pan or a linear drain so that a local low point does not become an internal leak.

Threshold Height, Set-Down and Structure

The height of the threshold relative to the two finished floor levels is the single most consequential decision at a door opening, and it is usually made by default rather than by design. Three conditions are possible. The threshold may sit above the external surface, which is the most forgiving arrangement for water and the least forgiving for access. The threshold may sit flush, which requires the structure to be set down so that the frame, the pan, the membrane and the finish can all occupy the same depth. Or the threshold may sit below the internal floor, forming an internal step, which is common at wet areas and balconies but must be deliberate.

Set-down has a structural consequence. A slab that is set down at a door opening must be reinforced and detailed for it, and the set-down must be shown on the structural drawings, not discovered by the door installer. Where the set-down is insufficient, the alternatives are a raised threshold, a low-profile track that depends more heavily on seals, or a change to the floor build-up. Each alternative should be recorded, because each carries a different maintenance burden.

Site Verification

Levels should be checked at defined hold points: after the slab or frame is complete, after the screed or topping, and after the waterproofing but before the finish. A laser level and a photographic record at each stage cost very little. Rebuilding a threshold after a floor has been laid is a different order of expense, and it is rarely done properly, because by then the frame, the membrane and the finishes are all in the way.

Seals at the Threshold

Seals at a threshold perform two jobs that are often confused. Some are weather seals, intended to resist air and water movement. Others are movement joints, intended to accommodate differential movement without transferring stress into the frame or the finish. A product selected for one duty rarely performs the other well.

Compression Seals, Wipe Seals and Sill Seals

Compression seals rely on being compressed between two surfaces to form a barrier. Their performance depends on the compression being within the range the seal was designed for, which in turn depends on the door being correctly hung and the frame being correctly set. A compression seal that is over-compressed takes a set and stops recovering; one that is under-compressed does not seal at all.

Wipe seals are flexible blades that sweep across a surface as the door moves. They tolerate variation in the gap and are effective against air movement and light water, but they are not a pressure barrier. Sill seals sit at the bottom of the leaf and bear on the threshold; they take the most wear of any seal in the assembly and are the first to require replacement.

Sealant Selection and AS 4284

Sealants used at the threshold are structural in the sense that they must remain adhered through movement and weathering. Their selection should be based on the substrates involved, the movement expected, the exposure, the compatibility with the adjacent membrane and the finish, and the ability to be reapplied later. AS 4284 provides the test methods used to evaluate building sealants, and a specification that references it is asking for evidence rather than a claim.

Two practical rules matter more than any data sheet. First, sealant is not a substitute for a flashing; it is a supplement to one. Second, a sealant joint that is designed as a fillet in a corner will fail in shear as the joint moves, whereas a joint designed with a backing rod and the correct profile can accommodate movement. The shape of the joint is part of the design.

The Seal Path Must Close

Air and water sealing at a door depends on a continuous line from jamb to head to jamb to sill and back. That line passes through corners, through fixed and opening junctions, through the interface with the wall membrane and through the threshold. Every interruption is a potential leak. The most common interruptions are at the bottom corners of the frame, where the sill flashing, the jamb flashing, the pan and the sealant all meet within a small volume and where access for a proper seal is difficult.

A useful discipline is to draw the seal path as a single line on the detail, in the same way an electrician draws a circuit, and to check that the line is unbroken. If the line has to jump, the jump is a defect in the detail, not a detail to be resolved with more sealant.

Flashings and the Envelope Interface

Flashings do the work that sealant cannot: they shed water by gravity and by overlap. At a door opening, the flashing regime has to connect the sill to the wall, the wall to the frame, and the frame back to the wall, without creating a path for water to enter the construction.

Sill Flashings and Their Termination

A sill flashing sits under or behind the sill and turns up at each end into the jamb. Its purpose is to intercept water that reaches the base of the opening and deliver it to the exterior, in front of the wall’s weather-resistant barrier. The critical details are the end upturns, the lap over the wall flashing below, and the termination at the face of the wall, where the flashing must finish in a drip rather than a flat edge.

Terminations are where flashings and membranes compete for the same space. The wall’s weather barrier, the door’s sill pan and the flashing all have to be lapped in the correct order, shingle fashion, so that each layer sheds onto the one below. When the order is reversed, water is trapped between layers and the assembly behaves as a reservoir.

Head and Jamb Flashing Continuity

The head flashing is often well executed because it is visible and its purpose is obvious. The jamb flashing is less so, and the junction between head and jamb is the point where many otherwise sound details fail. The head flashing must lap over the jamb flashing, and both must lap over the sill, so that the assembly drains downward and outward without a reverse lap anywhere.

Where a door sits within a recess, a balcony or a deep reveal, the flashing regime also has to deal with water that runs down the reveal and along the soffit. A recess protects the door from direct rain, but it concentrates runoff at the base of the reveal, which is often directly in front of the threshold.

Dissimilar Metals and Isolation

Aluminium, steel, stainless steel, copper and zinc all behave differently when they are wet and in contact. Galvanic corrosion at a threshold is common where aluminium frames meet steel reinforcement, mild steel flashings, or fixings of the wrong grade, and it is accelerated in coastal and industrial environments. The remedies are material selection, isolation tapes and washers, and the avoidance of trapped moisture at the interface.

Cut edges of coated aluminium are particularly vulnerable, because the coating that protects the face does not protect the cut. Where a sill section is cut on site, the cut should be treated as the supplier requires, and the detail should not place the cut edge where water will stand.

Waterproofing Boundaries and Wet-Area Interfaces

An interior wet area is a room designed to get wet. A bathroom, a laundry, a shower, an ensuite, a commercial washroom: each has a floor that will be wet regularly, and each has a boundary where the waterproofing system stops. The door threshold is frequently that boundary, which makes it the most vulnerable line in the room.

Where the Membrane Stops

The membrane must extend to a termination that is above the wet area’s flood level and that is fixed and sealed independently of the finish. At a doorway, the termination is usually an upturn at the frame or a stop at the threshold, and the critical question is what happens to water that reaches the door. If the membrane stops at the internal face of the frame and the frame is sealed to the floor, the threshold becomes a dam. If the membrane is turned up and the door is detailed with a step or a raised sill, the water stays inside the room where the drainage is.

Waterproofing in domestic wet areas in Australia is governed by AS 3740, and the standard sets out where membranes are required, how they must turn up, and how penetrations and junctions are treated. In New Zealand, Clause E3 Internal Moisture of the Building Code governs, supported by the acceptable solutions. In both jurisdictions, the membrane system is a proprietary system, and it must be installed as a complete system by an applicator who is competent in that system. Mixing products from different manufacturers at a junction is a common cause of failure.

The External and Internal Boundary

Where a door separates an internal wet area from the outside, the threshold must satisfy both the internal waterproofing regime and the external weathertightness regime. Those regimes have different logic. The internal regime assumes water on the floor and relies on containment and drainage to a waste. The external regime assumes water on the outside face and relies on shedding, flashing and pressure management. The threshold has to do both, and the two systems must be joined without either one terminating in the other’s wet zone.

A common and effective principle is to keep the two drainage systems separate and to make the junction between them a raised element, so that water from the internal floor cannot reach the external door line by gravity. Where a level threshold is required for access, the internal drainage must be designed to remove water before it reaches the door, and the door assembly must be detailed with a pan and a secondary seal.

Balconies, Terraces and Roof Terraces

A door onto a balcony is a wet-area interface even though the room inside may be dry. The balcony is an external floor that collects rain, and the door is the point at which that floor meets the building. The threshold must therefore be detailed with the balcony’s waterproofing, its fall, its drainage outlet and its flashing all coordinated, and the door must not be installed until the balcony membrane has been tested and accepted.

Flooring Transitions

The flooring transition at a threshold is the visible result of everything beneath it, and it is the part the client will judge. It is also the part most likely to be changed late, when a finish is substituted or an owner decides on a different tile.

Tile, Stone, Timber, Vinyl and Carpet

Each finish behaves differently at a threshold. Tile and stone are rigid and dimensionally stable but require a substrate that will not deflect, and their edges need a trim or a rebate. Timber moves with moisture and requires a gap and a movement joint at the door line. Vinyl and resilient finishes are thin, which changes the height of the transition and often requires a separate transition strip. Carpet is compressible and hides small differences in level but traps water and dirt at the door line.

The transition detail should be drawn for the specific pair of finishes on each side, not for a generic condition. Where the internal finish is not yet selected, the detail should state the range of thicknesses the threshold can accommodate, and the frame height should be set accordingly.

Trims, Grates and Linear Drains

A transition trim covers the junction and protects the edge of the finish. It should be fixed to the substrate, not to the finish alone, and it should not create a barrier to drainage. A threshold grate or a linear drain at the door line can be an effective way to intercept water before it reaches the frame, but only if it is accessible for cleaning and if its outlet is connected and graded correctly. A linear drain that cannot be cleaned becomes a long, shallow reservoir.

Movement and Differential Settlement

The internal and external floors are usually supported differently and will move differently. A rigid transition that bridges both will crack or debond. The detail should therefore include a movement provision at the door line, concealed within the trim or the threshold, so that movement is accommodated rather than resisted.

Glazing at the Threshold

The glazing in a door is part of the threshold assembly, not a separate subject. Glass adds weight, it changes the way the leaf behaves when it is closed, and it introduces its own sealing and safety requirements.

Safety Glazing Under AS 1288

AS 1288 governs the selection and installation of glass in buildings, including the circumstances in which safety glazing is required, the marking of glazed panels, and the installation tolerances that protect the glass from edge damage. Doors are a location where glazing is likely to be human-impacted, and the specification should nominate the glazing type for each panel rather than leaving it to the fabricator’s default.

Glass edges are the vulnerable part. A glass edge that sits in water, or that bears on a hard point, or that is chipped during installation, is a future breakage. The threshold detail should ensure that the bottom edge of the glass is held clear of any water path and that the glazing pocket drains as the system requires.

Glazing Beads, Gaskets and Drainage

The glazing pocket in an aluminium door is a small cavity with its own drainage and ventilation requirements. Weep slots in the bead or the sash allow water that passes the outer gasket to escape. If those slots are sealed during painting or blocked by a poor gasket installation, water stands against the glass edge and the gasket. The gasket itself must be continuous, correctly mitred at corners, and of a material suited to the exposure.

Door Bottoms and Finned Doors

A glass-finned door, where the glass extends to the bottom of the leaf, has no bottom rail to house a sill seal. The seal must then be a channel or a shoe, and the threshold must be shaped to receive it. These doors demand closer attention to the sill and to the drainage path, because the bottom of the glass is close to the water and because the seal has less structure to bear against.

Maintenance and Inspection

Threshold drainage is a maintained system, not a permanent one. Every element in it either moves, wears, collects debris or degrades under ultraviolet light. A door that drains correctly on the day of handover will not necessarily drain correctly after a season of pollen and a winter of wind-driven rain.

A Practical Routine

Cleaning should follow the exposure rather than the calendar. Coastal sites, sites with trees nearby, and sites with significant airborne dust need more frequent attention than sheltered urban sites. The routine itself is simple: clear the track and the weeps of debris, check that water leaves when the surface is wetted, inspect the sill seal and the corner sealant for cracking or separation, check that the door closes against the seal without forcing, and confirm that the drainage outlet is clear.

Alongside the door itself, the external surface should be checked for ponding and for any reversal of fall, the drain or grate in front of the door should be cleared, and the surrounding sealant joints should be inspected for adhesion loss. Where a sill pan has an accessible outlet, it should be checked with the same discipline as a roof gutter.

Testing for Water Ingress

The most useful test is also the simplest: direct a controlled flow of water at the threshold from outside, at an angle that simulates wind-driven rain, and observe both the internal face and the space below where accessible. A hose test is not a substitute for a laboratory test under AS 2047, but it identifies blocked weeps, reversed laps and open corner joints far earlier and far more cheaply than a complaint from an occupant.

Where water appears internally, the source should be traced before sealant is applied. Adding sealant to the inside face of a leaking threshold traps water in the assembly and moves the damage into the structure, where it is more difficult and more costly to find.

Records

The maintenance record should capture what was inspected, what was found, what was done and what remains outstanding. Photographs taken before finishes are laid are the only permanent record of the pan, the flashing and the membrane termination. They should be retained with the building documentation and referenced in the handover manual, because every future investigation of a leak will begin with them.

The Regulatory Framework

Threshold drainage sits at the intersection of several parts of the regulatory system, and none of them deals with it in isolation. The framework sets outcomes and methods; the project documents have to translate them into a buildable detail.

The NCC and the ABCB

In Australia, the National Construction Code, maintained by the Australian Building Codes Board, sets the performance requirements for weatherproofing, waterproofing, structural performance, access and glazing. The NCC is performance-based, which means it states the outcome required and then offers compliance pathways, including deemed-to-satisfy provisions and referenced standards. A threshold detail complies because it satisfies the relevant performance requirement, not because it looks like a detail in a magazine.

Volume One of the NCC applies to commercial and multi-residential buildings, and Volume Two to domestic construction. Both contain provisions relevant to wet areas, weatherproofing of openings and the interfaces between them. The NCC also references AS 3740 for the waterproofing of domestic wet areas, which is the standard most often engaged when a bathroom or laundry door is in question.

The Australian Standards

AS 2047 is the central standard for windows and external glazed doors in buildings. It sets out performance requirements and the test methods used to demonstrate them, including resistance to water penetration under pressure. A door assembly’s water performance is therefore a tested characteristic of a complete assembly, not a property of a sill profile, and the test report should match the configuration actually being supplied.

AS 1288 governs glass in buildings, including selection for location and the installation requirements that protect the glass. In a door, it determines when safety glazing is required and how the glazing must be marked and installed.

AS 4284 provides the test methods for building sealants. Referencing it in a specification requires evidence of performance rather than a manufacturer’s assertion, and it is particularly relevant at the threshold, where sealant is asked to perform in a wet, moving and exposed location.

AS 4666 is called up in many specifications for the installation of window and door assemblies and for the treatment of the frame-to-building junction, alongside the manufacturer’s installation instructions; the edition cited in the project documents governs which requirements apply. Installation is where tested performance is either preserved or lost, and a specification that names the standard, the fixing regime and the sealing requirements gives the installer something to be held to.

Other standards are drawn in as the project requires: AS 3740 for wet-area waterproofing, AS/NZS 4858 for wet-area membranes, and the relevant loading and structural standards for the support of the frame and the set-down.

New Zealand References

In New Zealand, the Building Code sets performance requirements through its clauses. Clause E2 External Moisture deals with the control of water from outside, and Clause E3 Internal Moisture deals with moisture generated inside a building, including wet areas. Both are supported by acceptable solutions and verification methods, of which E2/AS1 is the most familiar for residential construction.

E2/AS1 addresses the weathertightness of openings, including the need for flashings, the treatment of the frame-to-cladding junction and the management of water at the base of an opening. For glazing, NZS 4223 sets out the requirements for glass in buildings, including safety glazing in doors. Where a project uses a proprietary door system, the supplier’s installation requirements sit alongside these documents, and the building consent documentation should show how both are satisfied.

New Zealand practice places strong emphasis on the drained and ventilated cavity behind the cladding, and the door threshold is the point where that cavity terminates. The detail must allow the cavity to drain and vent at the base of the opening while still closing the building to water and air. That is a demanding combination, and it is one of the reasons New Zealand details at door openings tend to be more explicit than their Australian equivalents.

Specification and Quality Assurance

Most threshold failures can be traced to a document that was silent when it should have been specific. The specification does not need to draw the detail, but it must state the performance required, the standards that apply, the sequence of work and the evidence that will be accepted.

What the Specification Should State

The specification should nominate the door system and its tested configuration, including the weeps and the sill. It should state that the assembly is to be installed to the manufacturer’s instructions and to the named installation standard, and that no modification to the drainage features is permitted without the supplier’s written acceptance. It should require a sill pan of a nominated type, continuous and turned up at the ends, with a discharge point coordinated with the flashing.

It should define the flashings, their material, their laps and their termination, and it should require the wall’s weather barrier, the pan and the flashing to be lapped in the correct order. It should identify the waterproofing standard and system for any adjacent wet area, and require the membrane to be terminated independently of the finishes. It should require falls to be verified on site before finishes are laid.

Finally, it should require records: photographs of the pan, the flashing, the membrane termination and the sealant joints before they are covered, and a maintenance schedule at handover.

Hold Points and Inspection

A small number of hold points will catch most problems. Inspect the opening and the set-down before the frame is installed. Inspect the pan, the flashing and the membrane termination before the finishes go down. Inspect the seal path and the weeps before handover. Test with water before the building is occupied.

Each hold point should have a named person responsible for releasing it, and the release should be recorded. Where a hold point is released without inspection, the record should say so, because an undocumented release is indistinguishable from an uninspected one when a problem appears later.

Coordination Between Trades

The threshold is built by at least four trades in sequence: the structural contractor, the waterproofer, the door installer and the floor finisher, with the flashing installer somewhere in between. Each one can compromise the work of the others, and none of them owns the finished result. A short coordination meeting at the start of the works, with the detail on the table and the sequence agreed, is the cheapest form of quality assurance available at a door opening.

Frequently Asked Questions

Why does my aluminium door leak only in certain weather?

Because the leak is driven by pressure and direction rather than by gravity alone. Wind from a particular quarter pressurises the door face and forces water through paths that remain dry in still air. The likely culprits are blocked weeps, an open corner in the seal path, or a sill that sheds inward under pressure.

Can I seal the weeps to stop draughts?

No. Weeps are part of the drainage and ventilation design of the assembly, and sealing them converts a drained system into one that holds water against the inner line. If draughts are the concern, the correct response is to address the weather seal and the door adjustment, not the drainage path.

Is a sill pan necessary if the door has a good seal?

The pan is a secondary defence, and secondary defences exist because primary ones fail. Seals wear, weeps block and sealant debonds. A pan ensures that a failure of the primary line does not admit water into the structure. Where the door sits above a habitable space, or where the threshold is flush and the floor build-up is shallow, the case for a pan is strongest.

How much fall should the threshold or the external paving have?

That is a project-specific decision. It depends on the area, the surface, the exposure, the drainage outlet and the tolerances that can realistically be achieved. It should be designed with the construction tolerance in mind, shown on the drawings, and verified on site before finishes are laid rather than stated as a generic figure.

Can a level threshold be both accessible and watertight?

Yes, but it demands more from everything else. A level threshold removes the upstand that normally provides the mechanical stop against wind-driven water, so the drainage, the pan, the seals and the internal floor drainage must all be designed to compensate. It is a system decision, not a profile decision, and it should be supported by a tested assembly and a documented detail.

Who is responsible for the threshold detail?

The designer owns the detail, the structural engineer confirms support and set-down, the hydraulic consultant confirms drainage, the door supplier confirms the tested system and its installation requirements, and the builder confirms the sequence. Where that ownership is unclear, the threshold becomes the place where every unresolved interface appears at once, generally during the first significant rain.

Conclusion

Aluminium door threshold drainage is not a product category. It is a junction where water management, structure, access, waterproofing and finish all meet within a narrow band of construction, and where the consequences of a poor decision appear somewhere else entirely.

The principles are consistent even though the details are not. Provide a continuous path for water to leave, and a secondary defence beneath the frame for the water that does not. Keep falls and levels as explicit design decisions, verified on site. Close the seal path as a single continuous line. Lap flashings in the correct order and terminate them in a drip. Keep the internal wet-area membrane and the external weathertightness system separate, and make the junction between them a deliberate element rather than an accident of construction. Detail the flooring transition for the actual finishes. Protect the glass edges and the glazing drainage. Then maintain the whole assembly, because none of it is permanent.

The regulatory framework, from the NCC and the ABCB through AS 2047, AS 1288, AS 4284 and AS 4666, and in New Zealand through Clauses E2 and E3, E2/AS1 and NZS 4223, sets the outcomes and the methods. It does not draw the detail. That remains the work of the designer, the supplier and the installer, working from a documented sequence and a tested system, on a detail that is resolved before the slab is poured rather than after the floor is laid.

Aluminium Door Threshold Drainage: Sills, Weeps and Wet-Area Interfaces