Aluminium Door Sill Transitions: Floors, Drainage, Accessibility and Weather Seals

A door sill is the narrowest element in the building envelope and one of the busiest. Within a strip that is often no wider than the frame itself, the sill has to shed water, carry the door, close the gap between two different floor finishes, survive being walked over and cleaned, and sometimes provide a step-free route for a wheelchair or a pram. When the detail works, nobody notices it. When it fails, the symptoms appear far from the cause: a damp patch at the skirting, a swollen timber floor, a corrosion bloom on the threshold plate, a trip hazard at a balcony door, or a failed waterproofing inspection that stops the project at practical completion.

This guide sets out the design and coordination issues that determine whether an aluminium door sill transition performs. It deals with the threshold as a system rather than a product, covering surface-mounted, recessed and raised options, the relationship between the sill and the floor build-up, drainage and falls, weather seals, flashings, finishes, accessible design, renovation work, quality assurance and the Australian and New Zealand regulatory framework. It deliberately avoids nominal dimensions, because the correct height, width, fall and clearance on any project are set by that project’s floor build-up, exposure, drainage design and access requirements, not by a generic detail copied from a brochure.

The Sill as a System, Not a Line on a Detail

Four Performances Meeting at One Line

Every external door threshold resolves four separate performance requirements at the same location. The first is weathertightness: the assembly must resist rain, wind-driven water and air leakage without allowing water to reach the interior. The second is structural: the door leaves, the frame and any glazed panels must be supported, restrained and connected to the building so that loads are transferred safely and the frame does not distort. The third is the level transition: the interface between the internal floor finish and the external surface must be buildable, durable and, where required, usable by everyone. The fourth is durability and finish: the exposed metals, coatings, sealants and adjacent materials must survive the local environment, including salt, UV, cleaning chemicals and abrasion from foot traffic.

These requirements pull in different directions. A generous upstand helps keep water out but creates a step. A flush threshold is excellent for access but leaves very little depth for drainage and flashing. A deep recessed sill gives the best of both, but it demands an accurately formed rebate, an earlier decision on finished floor levels and a waterproofing detail that can be inspected before the frame goes in. Most sill failures are not failures of any single product; they are the result of one of these four requirements being optimised at the expense of another and nobody noticing until the building is occupied.

Who Owns the Interface

The threshold sits between disciplines, which is why it is so often under-detailed. The architect or designer sets the intent and the visual relationship between inside and outside. The structural engineer determines the slab, the rebate and the support conditions. The hydraulic or drainage consultant determines where water goes and how the external surface falls. The waterproofing contractor owns the membrane and its termination. The window and door supplier owns the frame, the sill section, the seals and the drainage path within the system. The builder owns the setting-out and the sequence. The building surveyor or certifier confirms that the installed result satisfies the applicable provisions.

No single party can resolve the threshold alone. The practical rule is that the interface must be drawn once, at a scale where the floor build-up, the membrane, the flashing, the frame, the seal and the external finish are all visible together, and then signed off by the parties who own each layer before the slab is poured. If the only drawing of the sill is a manufacturer’s standard section with a note saying “builder to suit site conditions”, the project has not designed the transition at all.

Threshold Types: Sill, Recessed and Raised

Surface-Mounted and Rebated Sills

The most common arrangement in residential and light commercial work is a sill section fixed to the top of the slab or to a prepared rebate, with the door frame sitting on or behind it. The sill typically incorporates a raised front nose or a rebate that encourages water to drip clear of the wall below, and a sloped or stepped profile that directs water towards the outside face. Some sections include a drainage chamber behind the front upstand, with outlets or weep paths that discharge onto the external paving or into a sub-sill drainage layer.

Surface-mounted sills are straightforward to install and easy to replace, which makes them common in renovation. Their weakness is depth: because the section sits above the structural slab, the difference between the internal finished floor and the top of the sill has to be absorbed somewhere. If the internal floor is tiled on a screed and the external surface is paving on a bedding layer, the sill can end up sitting proud of the internal floor, creating a small step at the very place where a flush transition was intended. On exposed sites, a shallow surface-mounted sill also offers limited protection against water being driven across the threshold.

Recessed Thresholds

A recessed threshold sets the frame and sill down into a rebate formed in the slab or in the structural build-up, so that the finished floor can run closer to the door line and the top of the sill can sit at or near the internal floor level. The rebate also creates room for a sub-sill flashing, a drainage layer and a continuous waterproofing termination below the frame, which is why recessed details are favoured where water management and level access both matter.

The trade-off is tolerance. A recessed sill is only as good as the rebate. If the rebate is formed in the wrong place, at the wrong level, or with the wrong fall, the frame either will not sit correctly or will sit correctly only after the waterproofing has been compromised to make it fit. The rebate must therefore be set out from the finished floor level, not from the structural slab, and it must be inspected and recorded before the frame is installed. Recessing also makes later replacement harder, because the new frame must match an existing rebate that was built for a different product.

Raised Thresholds and Step-Down Details

A raised threshold introduces a deliberate upstand between the internal floor and the external surface. It is a legitimate and often necessary response where the external level is close to or above the internal floor, where the site is highly exposed, or where a balcony or terrace drains towards the door and the designer wants a physical barrier rather than relying on the door seal alone. The upstand provides a positive stop for water and gives the flashing and membrane a height to terminate against.

The trade-off with a raised threshold is paid on the accessible route. Any upstand is a step, and a step has to be either eliminated, ramped, or accepted as a deliberate change in level with the consequences that follow for access, door hardware and the adjoining landing. A raised threshold that appears on an architectural drawing as a neat line becomes a trip hazard, a drainage ponding point or a compliance argument on site unless the access implications are resolved at the same time as the waterproofing detail.

Choosing Between Them

The choice is driven by five questions. How exposed is the facade, and how much wind-driven rain will reach the door? How much depth is available between the structural slab and the finished floor? Does the door slide, hinge or pivot, and how much room does the track or the leaf need? Is the door on a continuous accessible path? And how easily can the detail be built, inspected and later maintained on this particular site? The answers usually point to one family of details and rule out the others before any product is selected.

Floor Build-Ups and the Transition

Reading the Build-Up from the Slab Up

The single most common cause of a poor sill detail is that the frame was ordered against the structural slab level while the finished floor was still a nominal figure on an architectural drawing. Between the slab and the finished surface there may be a levelling screed, a waterproofing membrane, an insulation layer, a heating system, a bedding layer and the floor finish itself. Each of those layers has a thickness that is nominally specified but actually varies across a real slab, and the frame has to sit at the top of the finished assembly, not at the top of the structure.

This means the sill height is a downstream consequence of decisions taken by other people. The tiler’s bedding depth, the screed contractor’s tolerance, the membrane thickness and the finished floor selection all move the level that the door frame must meet. If those decisions are made after the frame is manufactured, the transition is resolved on site with packers, additional trims or a bead of sealant, none of which is a designed detail. The correct sequence is to fix the finished floor levels and the build-up first, then set the sill and frame, then confirm the external levels against the drainage design.

Tolerances and Setting-Out

Every construction element has a tolerance, and the sill sits at the point where several tolerances accumulate. The slab may not be flat, the rebate may not be square, the wall may not be plumb and the floor finish may not be level to the drawing. A well-designed transition absorbs these variations in a controlled way, through a adjustable connection, a cover bead, a movement joint or a deliberate bedding zone, rather than by forcing the frame and hoping the sealant takes up the difference.

Setting-out should be recorded. A survey of the slab and the rebate before the frame is fabricated, and a second check before installation, is far cheaper than remaking a frame or rebuilding a threshold. On projects with repeated door types, a mock-up of the typical detail, built and inspected before the production run begins, exposes the accumulation of tolerances while there is still time to change the design.

Inside, Outside and the Wet Area Interface

Internally, the threshold may meet tile, timber, vinyl, carpet or a recessed mat well. Each of these finishes has its own thickness, its own movement behaviour and its own detailing requirement at the door line. A carpet that is tucked against the frame, a tile that finishes with a metal edge trim and a timber board that needs an expansion gap all demand different sill geometries. The transition should be drawn for each finish type on the project, not averaged into a single generic detail.

Externally, the surface may be paving on bedding, a timber deck, a concrete slab with a applied coating, or a gravel or permeable surface. Each of these has a different relationship to the door: paving can bridge a drainage outlet, a deck can move independently of the building, and a permeable surface can direct water towards the threshold if the surrounding levels are not thought through. The detail must show how the external surface is kept clear of the drainage path and how it is supported where it meets the sill.

Drainage, Falls and Water Management

Where the Water Actually Goes

Water reaches a door sill in three ways: rain falling directly on the threshold, rain running down the door face and the wall above, and wind-driven rain being pushed against the assembly under pressure. A well-resolved sill handles all three with a defined path. Water on the threshold is directed outward by the sill profile. Water on the door face is collected by the frame’s own drainage system and discharged through outlets at the sill or the base of the jambs. Water driven past the primary seal is intercepted by a secondary drainage path and led out before it can reach the interior.

The critical principle is that the door should never be the primary drainage system for the building. If the external paving falls towards the door, or if the threshold is the lowest point on a balcony, the sill is being asked to cope with water that the design should have removed elsewhere. Good practice keeps the external surface falling away from the building, provides a drainage outlet or linear drain where water would otherwise collect, and treats the door as a barrier rather than a drain.

Falls Are Project-Specific

The fall on an external surface, the fall across a threshold, and the fall on a balcony or terrace are all determined by the project’s drainage design, the surface material, the exposure and the applicable requirements. There is no universal figure that can be transplanted from one project to another. A paved terrace with large format tiles, a timber deck with gaps, a concrete balcony with a membrane and a roof terrace over habitable space each behave differently, and each requires the designer to nominate a fall that will actually drain in service, allowing for construction tolerance and for the deflection of the structure.

What can be stated generally is the direction of the logic: water must be given a path away from the opening, the path must be continuous, and the path must remain clear for the life of the building. A fall that works on the drawing but terminates in a drainage outlet that the landscaper buries, or that runs into a paving joint that silts up, is not a drainage design. The threshold detail should show the outlet, the fall and the maintenance access, not just the door.

Sub-Sill Drainage and Weep Paths

Many aluminium door systems rely on a drained and back-ventilated principle: water that passes the external face is collected in a chamber within the sill or in a sub-sill cavity and discharged through weep slots, outlet spouts or a drainage layer below the frame. For that principle to work, the outlets must be open, positioned so that water does not have to rise before it can escape, and protected from blockage by mortar, sealant, paving or debris.

Sub-sill drainage is particularly important on recessed thresholds, where the frame sits below the external surface and water has nowhere to go unless it is collected and led out. The detail must show the drainage layer, the outlet, the flashing that separates it from the structure, and the inspection access. It must also show what happens at the ends of the sill, because water that reaches the jamb has to be turned out rather than allowed to run into the wall cavity or behind the membrane.

Ponding, Staining and the Second Line of Defence

Ponding is the visible symptom of a drainage design that does not work. Water that sits against a threshold will eventually find a path through a seal, a joint or a fixing, and it will leave a tide mark on the paving, the door face or the adjacent wall. Staining is not only an appearance issue; it is evidence that the assembly is wet where it should be dry, and it usually precedes corrosion, mould or timber decay.

The robust approach is to design two lines of defence. The first is the external face: the sill profile, the door seal and the weather seal that shed the bulk of the water. The second is the concealed drainage path: the flashing, the sub-sill, the cavity and the outlets that deal with whatever gets past the first line. A detail that relies on a single line of defence, however well that line is installed, has no redundancy, and redundancy is what separates a threshold that survives a storm from one that merely survives a sunny week.

Weather Seals and Air Infiltration

Compression Seals and Wipe Seals

Door seals fall into two broad families. Compression seals are deformed when the door closes, typically by an EPDM or silicone bulb or blade that is squeezed against the frame or the sill. They provide a positive barrier at the head, the jambs and the threshold, but they depend on the door being correctly adjusted so that the compression is consistent along the whole perimeter. Wipe seals, by contrast, rely on a flexible fin or brush that sweeps across a surface as the door moves. They are tolerant of small variations in clearance and are well suited to sliding doors, but they provide less resistance to water under pressure.

Many systems combine both: a compression seal at the closing stile and the head, a wipe seal or a brush at the sliding leaf, and a sweep or drop seal at the bottom. The combination matters more than the individual components, because water and air will exploit the weakest point in the perimeter. A door with an excellent jamb seal and a poor sill seal leaks at the sill.

Continuity at Corners and the Seal Path

Seals fail at discontinuities far more often than in the middle of a run. Corners, butt joints, screw penetrations, drainage slots and the junction between the frame and the wall are all places where the seal path can be interrupted. A continuous seal path means that the line of defence can be traced without a break from one jamb, across the head, down the other jamb and across the sill, and that every intersection is either welded, moulded, gasketed or sealed in a way that maintains the line.

On site, the most common interruptions are avoidable. A sill seal that is cut short at the jamb, a corner that is mitred without a seal, a fixing screw driven through a gasket, or a sealant bead applied over a joint that should have been mechanically sealed. Inspection should follow the seal path physically, with the inspector tracing the line and recording every junction, rather than simply looking at the door from a distance.

Movement, Maintenance and Replacement

Seals are consumables. They compress, harden, crack and wear, and they are exposed to UV, heat, cold, dirt and cleaning chemicals. A threshold design that makes seals inaccessible or that requires the door to be removed to replace a sill seal will not be maintained, and an unmaintained seal is a leak waiting to happen. The specification should identify the seal materials, the expected inspection interval and the replacement procedure, and the maintenance manual should include the sill and door seals explicitly.

Seals must also accommodate movement. Frames move with thermal expansion, structures deflect, and buildings settle. A seal that is compressed to its limit at installation has no capacity to accommodate that movement, and it will either fail in tension or be forced out of its groove. The design should leave the seal operating within its intended range, and the installation should confirm that the door closes with consistent resistance rather than forcing the last few millimetres.

Flashings and the Wall Interface

Sill, Jamb and Head Flashings

The sill flashing is the element that takes water from the door and the wall above and delivers it to the outside face, clear of the structure and the wall cladding. A properly detailed sill flashing has a back dam or upstand at the inner edge to prevent water tracking inwards, end dams at the jambs to prevent it running sideways into the wall, a fall to the outer edge, and a drip or projection that keeps water away from the wall below. It must be continuous, sealed at laps and integrated with the wall’s weather-resistant membrane or sarking.

Jamb flashings and head flashings complete the system. The head flashing protects the top of the opening and directs water away from the frame; the jamb flashings close the ends of the sill and provide a continuous path from the head to the sill. The three elements are usually detailed as one assembly, because a sill flashing that is not turned up at the jambs is simply a tray that overflows into the wall at its ends.

Support, Packing and Load Path

A flashing is not a structural element, but it must be supported so that it does not pond, deflect or tear. The sill trimmer, the angle or the continuous support beneath the frame carries the door loads and keeps the sill straight; the flashing sits over it, and the drainage path runs above the flashing. Packing must not block the drainage path or bridge the flashing, and fixings must not penetrate the flashing in a way that creates a leak path without a seal.

The load path deserves the same attention as the water path. The door frame transfers its loads to the structure through its fixings and its base; if the base is packed only at the ends, the sill will deflect underfoot and the seals will open. Continuous or closely spaced support under the sill is a design decision, and it should be shown on the detail rather than left to the installer’s judgement.

Material Compatibility

Flashings, frames, fixings and sealants are often made from different materials, and the junction between them is where corrosion starts. Dissimilar metals in contact, in the presence of moisture, create galvanic corrosion; the less noble metal is consumed, and the joint that was meant to be watertight becomes a gap. The specification should nominate compatible materials, isolation tapes or coatings where dissimilar metals meet, and fasteners that are appropriate to the environment.

Sealants have their own compatibility rules. Some sealants are not suitable for use against certain coatings, some will not adhere to damp or dusty surfaces, and some will stain natural stone or discolour powder coating. The sealant should be selected for the joint, the substrate and the movement, and the application should follow the manufacturer’s instructions on surface preparation, primer and tooling.

Finishes and Durability

Anodised, Powder Coated and Mill Finish

The finish on a door sill is exposed to more abrasion than almost any other part of the frame. It is walked on, swept, washed, and sometimes scraped by furniture, bicycles and cleaning equipment. Anodised finishes offer a hard, integral surface with a metallic appearance; powder coatings offer a wide colour range and a thick, uniform film; mill finish offers no protection beyond the natural oxide layer and is rarely appropriate for an exposed external threshold.

The choice should be made for the environment as well as the appearance. Coastal sites, industrial atmospheres and locations with high humidity place greater demands on the coating, and the edges, cut ends and machined surfaces of a profile are the first places where a finish will break down. Cut ends should be treated or concealed, and any site cutting of coated profiles should be minimised and touched up according to the coating supplier’s instructions.

Protection, Cleaning and the Construction Phase

Most threshold damage happens before handover. Mortar, render, paint, plaster and construction debris are dropped on the sill, walked into the track and left to set. Mortar is alkaline and aggressive to some coatings and sealants; it also blocks drainage outlets and hardens in the seal grooves. Protection during construction, and a cleaning regime that removes debris before it sets, prevents a large proportion of the callbacks that occur in the first year.

Cleaning should be appropriate to the finish. Abrasive pads and strong acids can dull an anodised surface or attack a powder coating, and pressure washing directed at the sill can force water past the seals and into the drainage cavity faster than it can escape. The maintenance manual should specify the cleaning method, the frequency and the products, and it should identify the drainage outlets that need to be kept clear.

Accessible Design Coordination

The Accessible Route and the Threshold

Accessible design is governed in Australia by the access provisions of the NCC, including the Deemed-to-Satisfy provisions that reference the AS 1428 series for design for access and mobility, and in New Zealand by the access requirements of the building code together with NZS 4121. Those documents deal with the route as a whole: the approach, the landing, the door opening, the hardware, the threshold and the surface beyond. The threshold is one link in that chain, and a single step at the door can break an otherwise compliant route.

The coordination task is to reconcile the access requirement with the waterproofing requirement before either is built. A flush threshold with a recessed drained sill is often the way to achieve both, but it requires the slab rebate, the membrane, the frame and the finished floor to be set out together. A raised threshold may be acceptable where the change in level is resolved by a ramped landing or a designed step with the appropriate visual and tactile cues, but that solution has to be designed and shown, not improvised on site.

Door Hardware and the Approach

Accessibility is not only about the sill height. The door leaf width, the clearance at the opening, the type and operation of the hardware, the force required to open the door, the closing speed and the space available to approach and manoeuvre all affect whether the doorway works for a person using a wheelchair, a walker or a pram. A threshold that is perfectly flush but paired with a heavy door, a round knob and an obstructed landing is still an inaccessible doorway.

The landing on both sides of the door needs to be considered together with the threshold. A level landing allows a person to stop, operate the door and pass through; a landing that falls steeply away, or that is interrupted by a drainage grate or a step, undermines the benefit of a flush sill. The drainage design and the access design must therefore be coordinated, not developed in parallel and reconciled at the end.

Documenting the Access Decision

Where a project relies on a specific threshold detail to achieve access, that detail should be documented and referenced in the access report or the specification, with the door schedule noting the threshold type for each opening. The certifier or access consultant should see the detail, not just a note that the door is “accessible”. The same discipline applies to renovations and fit-outs, where an existing threshold may be the only thing standing between a compliant route and a non-compliant one.

Renovation and Retrofit

Replacing a Door in an Existing Opening

Renovation work starts with measurement, not with a catalogue. Existing openings are rarely square, plumb or the size the original drawings suggest, and the floor build-up may have changed since the building was constructed through subsequent tiling, re-screeding or the addition of a new floor finish. The new frame has to fit the opening as it actually is, and the new sill has to meet the existing floor and the existing external level.

The condition of the existing sub-sill is often the hidden issue. Timber sub-sills may be rotted, brickwork may be saturated, and the original flashing may be absent or ineffective. Removing the old frame exposes these conditions, and the renovation should allow for their repair rather than covering them with a new sill. A new door installed over a failed sub-sill will leak in the same place as the old one.

Adapting to Out-of-Level Floors

Where the internal floor and the external surface are already at an awkward relationship, the renovation has three broad options: adjust the door and sill to suit the existing levels, adjust the floor build-up, or introduce a designed step or ramp. Each has consequences. Adjusting the sill may create a step at the internal floor; adjusting the floor may affect adjacent rooms and services; introducing a ramp or step affects the accessible route and requires space that may not exist.

The decision should be made with the same information that a new build would use: finished floor levels, external levels, drainage, exposure and access. A renovation that simply matches the old detail inherits the old problems, and a renovation that changes the threshold without checking the drainage can create new ones.

Approvals and Existing Building Constraints

Renovation thresholds often sit within a web of constraints: strata or body corporate rules, heritage controls, party wall agreements, existing waterproofing warranties and the requirements of the certifier for the new work. Replacing a door in a heritage building may require the new sill to match the original profile while still meeting current weathertightness and access expectations. In strata buildings, changes to the common property or the external appearance may need approval before work starts.

The practical approach is to establish the approval requirements early, document the existing condition before demolition, and specify the new threshold in a way that can be inspected after the frame is installed. Renovation work is usually inspected at fewer stages than new construction, so the records matter more, not less.

Specification and Quality Assurance

What the Specification Should Contain

A door sill specification should state the performance required, the standards the system is expected to satisfy, the acceptable system or systems, the interface details, the materials and finishes, the seal types, the fixing and support requirements, the drainage requirements and the inspection regime. It should identify the doors that are on an accessible route and the doors that are exposed to wind-driven rain, because those openings need more attention than an internal door under a deep verandah.

The specification should also state what is not acceptable. Sealant-only joints where a mechanical seal is required, packers that block drainage, fixings through flashings without seals, cut ends left untreated and drainage outlets left buried are all common site practices that should be explicitly excluded. A specification that lists only the product and not the workmanship leaves the important decisions to the installer.

Hold Points and Inspection

The threshold should be inspected at defined hold points, because most of it is hidden once the building is complete. The first hold point is the slab or rebate: level, position, dimensions and fall. The second is the sub-sill flashing and the drainage layer, before the frame is installed. The third is the waterproofing termination and the membrane, before it is covered. The fourth is the frame and sill installation: support, packing, fixings, seal path and drainage outlets. The fifth is the sealant and the finished floor junction. The sixth is the final inspection of the door operation, the seals and the drainage, ideally with a water test.

Each hold point should have a recorded inspection and, where appropriate, photographs. On projects with many identical doors, inspecting the first one thoroughly and then sampling the rest is more effective than a superficial check of every unit, provided the sampled units are chosen to include the most exposed and the most constrained conditions.

Records and Handover

Handover should include the manufacturer’s installation instructions, the maintenance requirements for seals, finishes and drainage, and the records of the inspections carried out. The building owner needs to know that the drainage outlets exist and where they are, because the most common cause of a leaking threshold years after completion is a blocked outlet that nobody knew about.

The records also matter for the certifier. Evidence that the installed system matches the specified system, that the flashings and membrane were inspected before concealment, and that the door was adjusted and tested is what allows the project to demonstrate compliance rather than assert it.

Standards and Regulatory Framework

Australia: NCC and ABCB

In Australia, the National Construction Code is produced by the Australian Building Codes Board and is adopted, with variations, by each state and territory. NCC 2025 is structured in volumes: Volume One covers Class 2 to Class 9 buildings, while Volume Two and the ABCB Housing Provisions cover Class 1 and Class 10 buildings. The code works through performance requirements, deemed-to-satisfy provisions and the option of a performance solution, and the project team should confirm which volume and which edition apply in its jurisdiction.

For door thresholds, the relevant NCC provisions are distributed rather than gathered in one place. Weatherproofing of external openings, drainage and waterproofing of wet areas, access for people with a disability, energy efficiency of the envelope and structural performance all bear on the detail. The threshold is where those provisions meet, and the certifier is the person who confirms how they apply to the specific building.

Australia: The Referenced Standards

AS 2047 covers windows and external glazed doors in buildings, including their manufacture, installation and performance, and is the standard against which window and door systems are typically specified and tested. AS 1288 covers the selection and installation of glass in buildings, and AS 2208 covers safety glazing materials, which matters where a door incorporates glazing that could be subject to human impact. AS/NZS 4666 covers insulating glass units, and AS 4284 covers the testing of building facades, including the laboratory and field testing that supports claims about water penetration and structural performance.

Those standards define what compliance means for the products and systems they cover. They do not replace the project-specific design of the threshold, the drainage and the flashings, and a certificate for a window system does not certify the installation detail around it. The specification should cite the standards as performance references and require evidence that the supplied system has been assessed against them, while leaving the interface design to the project documents.

New Zealand References

In New Zealand, the building code is issued under the Building Act and is structured around clauses that deal with specific performance areas. External moisture is addressed by Clause E2, energy efficiency by Clause H1 and access by the access provisions of the code, with NZS 4121 providing design guidance for access and mobility. NZS 3604 is widely used for timber-framed construction, and the glazing and window performance standards include SNZ TS 4211:2022 and NZS 4223.

New Zealand practice places strong emphasis on the weathertightness of junctions, and the principles in this guide apply directly: a defined water path, a drained cavity or sub-sill, a continuous flashing, compatible materials and an inspected installation. Projects working across both countries should be careful not to assume that a detail accepted in one jurisdiction is accepted in the other, because the referenced standards, the testing regimes and the consenting processes differ.

Frequently Asked Questions

Can a door sill be completely flush with the internal floor?

Yes, in principle, but a flush threshold requires a recessed detail with a drained sub-sill, an accurately formed rebate and a waterproofing termination below the frame. The feasibility depends on the available floor build-up and the external levels. A flush sill that is achieved by simply omitting the upstand, without providing a drainage path, is likely to leak.

Why does water collect at the door after rain?

Water collecting at a threshold usually indicates that the external surface falls towards the door, that the drainage outlet is blocked or missing, or that the sill drainage slots are obstructed. It can also indicate that the door is being used as the drainage point for a balcony or terrace. The cause should be identified and corrected rather than managed with additional sealant.

Is a raised threshold always a problem for accessibility?

A raised threshold is a change in level, and changes in level need to be resolved as part of the accessible route. Depending on the project and the applicable access provisions, the solution may be a ramped landing, a designed step with appropriate cues, or a different threshold detail. The important point is that the decision is designed and documented, not left to the site.

How often should door seals be replaced?

Seal life depends on the material, the exposure, the amount of use and the maintenance regime, so a single interval cannot be applied to every door. The maintenance manual should set an inspection interval and describe the signs of deterioration: hardening, cracking, compression set, gaps at corners and visible daylight. Seals that are stiff or torn should be replaced rather than adjusted.

Can an existing door sill be replaced without removing the frame?

Sometimes, if the sill is a separate section that can be dismantled and the frame remains sound. In many systems the sill is integral to the frame or is sealed to it, and replacement requires removing the frame. The decision should be made after inspecting the system and the condition of the sub-sill, because a new sill over a failed sub-sill will not solve the leak.

Does the door supplier certify the installation?

The supplier typically certifies the product and provides installation instructions, while the builder and installer are responsible for executing the installation in accordance with those instructions and the project documents. The certifier confirms the installed work. Responsibilities should be stated in the contract and reflected in the inspection records.

What is the most common cause of threshold failure?

In practice, the most common causes are a floor build-up that was not coordinated with the frame, a drainage path that was blocked or omitted, a flashing that was discontinuous at the jambs, and a seal path that was interrupted at a corner or a fixing. Almost all of them are interface failures rather than product failures, which is why coordination and inspection matter more than the choice of a particular section.

Conclusion

A well-resolved aluminium door sill transition is the product of decisions taken long before the frame arrives on site. The floor build-up sets the level, the drainage design sets the fall, the exposure sets the seal and flashing strategy, and the access requirements set the permissible change in level. When those decisions are made together and drawn as one detail, the threshold does its job quietly for the life of the building. When they are made separately, the sill becomes the place where every unresolved interface is discovered at once.

The discipline is straightforward even if the execution is not: define the performance, fix the levels, design the water path, specify the seals and flashings, protect the finish, coordinate the accessible route, inspect at hold points and keep the records. Those steps do not depend on a particular product or a particular project, and they are the same whether the door is a new installation in a high-rise apartment or a replacement in a renovated house.

References

1. Australian Building Codes Board. National Construction Code 2025, Volume One and Volume Two, including the ABCB Housing Provisions. https://ncc.abcb.gov.au
2. Standards Australia. AS 2047, Windows and external glazed doors in buildings. https://www.standards.org.au
3. Standards Australia. AS 1288, Glass in buildings – Selection and installation. https://www.standards.org.au
4. Standards Australia. AS 2208, Safety glazing materials in buildings. https://www.standards.org.au
5. Standards Australia. AS/NZS 4666, Insulating glass units. https://www.standards.org.au
6. Standards Australia. AS 4284, Testing of building facades. https://www.standards.org.au
7. Standards Australia. AS 1428 series, Design for access and mobility. https://www.standards.org.au
8. Standards New Zealand. NZS 4121, Design for access and mobility – Buildings and associated facilities. https://www.standards.govt.nz
9. Standards New Zealand. NZS 3604, Timber-framed buildings. https://www.standards.govt.nz
10. Standards New Zealand. SNZ TS 4211:2022 and NZS 4223, glazing and window performance. https://www.standards.govt.nz
11. Ministry of Business, Innovation and Employment. New Zealand Building Code, Clause E2 External moisture and Clause H1 Energy efficiency. https://www.building.govt.nz

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