Reveal tolerances for windows and doors: what to accept on site

A window or door is a factory-made product being dropped into an opening built by other trades, on a different programme, usually in weather. The reveal tolerance is the allowance that makes that marriage possible. It is not a nicety and it is not a single number — it is a pair of obligations, one on the opening and one on the unit, and a claim only succeeds if you can show which side missed.

Most disputes about reveals are not really about the millimetres. They are about timing. A builder who measures the unit on the day it arrives, records the result, and notifies the supplier in writing before installation is in a completely different position from one who discovers the problem when the architrave will not close over the gap, three weeks after the units were signed for and stacked in the rain.

This article is about receival inspection and defect escalation. It assumes you already know how a reveal is framed and flashed. What it deals with is the commercial mechanism: how tolerance checking at the point of delivery converts a defect from your problem into the supplier’s problem, and what happens when it does not.

Why reveal tolerances exist at all

A structural opening is never exactly the size on the drawing. Formwork moves, frames are plumbed and braced to a practical standard rather than a theoretical one, and masonry is laid by people working to their own tolerances. If windows were manufactured to the exact nominal opening size, no window would ever fit. The reveal tolerance is the deliberate gap that absorbs the drift between trades.

That gap has to do two jobs. It has to be wide enough that the unit can be installed, packed, fixed, sealed and flashed without forcing anything, and it has to be narrow enough that the sealant joint and flashing detail still work. A joint that is too wide cannot be sealed reliably with the specified product and becomes a water path. A joint that is too narrow means the unit is jammed in, which racks the frame, throws the sash out of alignment and eventually shows up as a binding door or a leaking sill.

This is why tolerance is expressed in words in the governing documents rather than as a single magic number. The Australian Standard that covers window installation, the National Construction Code and the manufacturer’s own installation instructions all set out requirements, and they do not always use the same framing. The builder’s job is to establish, before ordering, which document governs the job, and to build the opening so that the unit and the sealing system both work. If you are unsure which figure applies, check the current edition of the relevant Australian Standard and the manufacturer’s instructions for the specific system you are installing.

The two sides of the tolerance obligation

It helps to think of every reveal as a joint between two independently manufactured things, each of which has its own acceptable range.

The opening has a tolerance. The frame or masonry has to be built square, plumb and to the specified opening size within an allowance. If the opening is out of square, the unit cannot be installed square without packing one corner and closing another, and the sealant joint will vary around the perimeter.

The unit has a tolerance. The frame has to be manufactured square within an allowance, and the overall dimensions have to sit within the range the supplier nominates. A unit that arrives out of square by more than the allowance is a manufacturing defect, not an installation problem, and it should be treated as a supplier claim from the moment it is identified.

The practical consequence is that you cannot resolve a reveal dispute by measuring the gap alone. You need two sets of measurements: the opening, taken before the unit is installed, and the unit, taken at delivery. With both, you can show whether the opening was built outside its allowance, whether the unit was manufactured outside its allowance, or whether both were within tolerance and the installer simply did not set the unit correctly. Without both, you are arguing from opinion.

What receival inspection actually has to cover

Receival is the point where risk passes. In most supply arrangements, once you sign the docket and the truck leaves, the supplier’s position hardens considerably. Damage that could have been attributed to transit becomes damage you accepted, and dimensional problems that could have been a manufacturing claim become a site problem.

That means receival inspection is not a glance at the wrapping. It is a structured check, done while the unit is still accessible, ideally while the delivery vehicle is still on site.

• Identity. Unit mark, size, handing, glazing specification and hardware schedule checked against the order and the shop drawings. Wrong handing is the single most common receival error and the most expensive to discover after installation.
• Frame dimensions. Overall width and height measured and recorded against the nominated size.
• Square. Diagonal measurements taken across the frame and compared. Diagonals that differ indicate the unit is out of square, whether from manufacture or from transit racking.
• Operation. Sashes and doors opened and closed through their full travel. If a sash binds on a unit that is standing flat on level ground, that is a unit problem, not an installation problem.
• Condition. Frames checked for distortion, dents and coating damage; glass checked for chips, scratches and seal failure; seals, gaskets, drainage slots and weepholes checked for damage or blockage.
• Labelling and documentation. Window energy rating labels and any compliance documentation present and traceable to the units supplied. The Window Energy Rating Scheme is the industry scheme for comparing the thermal performance of window products, and the label is the evidence of what was specified and what was delivered.

Record all of it. A receival inspection that is not written down is not evidence. The record should identify the unit, state the measurement or observation, and be dated and attributed to a named person on site.

Measuring the opening before the unit arrives

The strongest position a builder can be in is to have the opening measured and recorded before the units are delivered. This is not extra work; it is the evidence that makes every later conversation shorter.

Measure the opening at more than one point. Width at the head, the sill and the mid-height. Height at both jambs and the centre. Check the frame or masonry for plumb and square. Note any obstruction — a proud slab edge, a lintel that has deflected, a brick course that has run out — that will affect how the unit sits.

If an opening is outside the allowance, the decision point is now, not at installation. Options include correcting the opening before the unit arrives, ordering the unit to a revised size, or accepting a larger joint and changing the sealing and flashing detail to suit. The last option needs the manufacturer’s agreement in writing, because it may fall outside their installation instructions and could affect the product warranty.

This is where a lot of warranty arguments are lost. A builder who accepts an oversized opening and installs the unit without written agreement from the supplier has, in effect, varied the installation method. If water later gets in, the supplier will point at the installation, and they will have a document to point at.

Where energy performance documentation fits

Windows and doors are one of the largest determinants of how a home performs thermally, and the specification that was designed into the job — frame type, glazing, coatings, gas fill, spacer — is what the energy assessment was based on. A substitution at supply stage that is not documented can invalidate the design assumption even if the unit looks identical on site.

This matters for receival inspection because the check is not just dimensional. It is also a check that what was delivered matches what was specified. The rating label and the supplier’s documentation are the link. If you are working on a project where the glazing specification was driven by an energy assessment, the receival record should confirm the delivered units match, and any substitution should be raised and resolved in writing before installation. The related article on windows glazing and energy performance covers the specification side in more detail.

Deciding what to accept and what to reject

Not every deviation is a rejection. Rejecting a delivery that could have been adjusted on site costs programme time, storage and goodwill, and on a tight programme it can cost more than the defect. Equally, accepting a unit that cannot be made to perform is a decision that surfaces later as a leak, a binding door or a failed inspection.

The test is functional, not cosmetic. Ask whether the specified sealing and flashing system can still be installed and will still perform, and whether the unit can be installed without being forced. If the answer to either is no, the unit should not be installed as delivered.

Two practical rules reduce the argument. First, cosmetic damage that does not breach a coating or a seal is usually a site repair, but it should still be photographed and recorded so it cannot be attributed to you later. Second, any deviation that requires a change to the installation method, the sealant type or the joint size needs the supplier’s written agreement before you proceed. A verbal assurance from a delivery driver is worth nothing in a warranty claim.

Documenting a defect so it survives scrutiny

A defect record has one purpose: to let a third party who was not on site understand what you found, when you found it and why it matters. That means it needs five things.

• The unit identifier and the delivery docket number.
• The observation, stated as a measurement or a description rather than an opinion.
• The date and time, and the name of the person who made the observation.
• Photographs with a scale in frame, taken before the unit is moved or installed.
• The action taken: notified, held, installed under protest, or returned.

Send the notification in writing the same day, to the person named in the supply contract rather than to the driver. Keep the acknowledgment. If there is no acknowledgment, send a follow-up and keep a record of that too.

Where the defect is dimensional, attach the measurements of both the unit and the opening. This is the single most useful thing you can do, because it pre-empts the supplier’s first response, which is to blame the opening.

Escalation: the sequence that works

Escalation is a sequence, and each step depends on the records made at the previous one. Skipping a step rarely speeds things up; it usually means starting again.

The first step is the supplier, in writing, with the evidence. Most genuine manufacturing defects are resolved here, because a supplier who can see the measurement knows the argument is not winnable.

The second step, when the supplier disputes the claim or the tolerance itself, is to establish the governing requirement. Standards and tolerances guidance exists precisely to resolve these disputes, and there is published guidance from building and plumbing regulators aimed at helping builders and homeowners work out whether a variation is within tolerance or is a defect. The tone of that guidance is worth noting: it treats tolerance as a defined range, not as a matter of opinion, which is exactly the frame you want the conversation in.

The third step is contractual. The supply contract, the subcontract and the head contract each set out notice periods, defect liability arrangements and who carries the cost of removal and reinstatement. A window that has been installed and rendered before the defect is raised is a much more expensive claim, because the cost is no longer just the unit.

The fourth step, if the dispute persists, is the statutory and dispute resolution framework that applies to the project. That is where the earlier records do their work, because a claim supported by dated photographs and measurements is a different proposition from one supported by recollection.

Worked example: a delivery accepted too quickly

A builder in western Sydney is running a two-storey project with a fixed completion date. The window units arrive on a Friday afternoon. The supervisor is managing a concrete pour and signs the docket without opening the units, on the basis that the supplier is a regular and the units are wrapped. The units are stacked against a wall on the lower slab, in the weather, over the weekend.

On the following Wednesday the installer starts setting units. Two of the larger sliding units will not sit square in their openings. The supervisor measures the openings: they are within the allowance the frame carpenter was working to. The units are then measured on the ground: the diagonals differ, and one frame has a visible twist.

The supplier is contacted. Their position is that the units were signed for without qualification, that they have been stored on site for several days in the weather and out of their packaging, and that the distortion is consistent with site storage rather than manufacture. There is no receival record, no photograph from the day of delivery and no written notification. The builder ends up carrying the cost of the two units and the labour to refit them, and the programme slips by the lead time on replacements.

Now run the same scenario with a receival inspection. The supervisor opens the units on the Friday, measures the diagonals on the truck, photographs the twisted frame with a tape in shot, notes the docket number and emails the supplier before close of business. The supplier acknowledges. On the Wednesday, the same installer finds the same problem, but the claim is a manufacturing claim supported by a record made before the units were ever stored on site. The supplier replaces the units. The builder carries the delay but not the cost, and the next delivery is checked more carefully by everyone involved.

The difference between the two outcomes is not skill. It is about ten minutes with a tape and a phone, done at the right moment.

Common mistakes that turn a defect into your cost

• Signing the docket before inspecting. Once it is signed unqualified, the burden shifts to you to prove the damage predated delivery.
• Storing units badly. Units stored flat, in standing water or in a traffic path will distort, and distortion is the hardest defect to attribute.
• Raising defects verbally. A phone call to a driver is not notice under a supply contract.
• Installing under protest without written agreement. If you install a unit you have already identified as defective, you weaken the claim and take on part of the liability.
• Recording a defect without measurements. “Out of square” is an opinion. A diagonal measurement is evidence.
• Assuming the opening is right because the frame carpenter says so. Measure it yourself, before the units arrive, and keep the record.

Each of these mistakes has a cost attached, and the cost is almost always larger than the inspection would have been. The commercial reality of reveal tolerances is that they are cheap to check and expensive to argue about.

Where this sits in your CPD

Receival inspection, defect documentation and escalation sit at the intersection of contract administration, quality management and building compliance, which is exactly the territory NSW builder CPD is meant to cover. The skill being assessed is not whether you can recite a tolerance figure, but whether you can set up a job so that defects are identified, recorded and attributed before they become your liability.

If you want to build the full picture — how CPD requirements work for licensed builders in NSW, what counts and what does not — the NSW builder CPD guide sets it out. The course catalogue lists the modules that cover materials, quality and contract topics, and the PointCPD home page is the starting point for the platform. For the installation side of the same subject, the related article on window and door flashing and sill details covers how the joint you are protecting at receival actually gets sealed and drained.

Frequently asked questions

Do I have to inspect every unit on delivery?

Every unit should at least be checked for identity, handing and visible damage, and any unit that is difficult or expensive to replace should be measured and squared. Larger units and sliding units are the ones most likely to arrive distorted, so prioritise those. If the delivery is large, split the inspection with a second person and record who checked what.

What if the supplier refuses to accept a defect claim?

Ask them to state, in writing, the tolerance they are relying on and the document it comes from. Then compare it against the measurements you recorded at delivery. If the documents conflict, published standards and tolerances guidance is designed to resolve exactly this kind of dispute, and the contract sets out the next step.

Can I install a unit that is slightly out of square?

Only if you can install it so that the sash operates freely and the specified sealing and flashing system still performs, and only with the supplier’s written agreement. Installing a distorted unit and forcing it square can crack glazing, damage seals and void warranties. If in doubt, hold the unit and escalate.

Who pays when an opening is outside tolerance?

It depends on which trade built the opening and what the contract says about coordination. The practical answer is that the builder carries the risk unless the responsible subcontractor has been given clear notice and the opportunity to correct. That is another reason to measure openings before the units arrive rather than after.

Does the energy rating label matter at receival?

Yes, because it is the evidence that the delivered product matches the specification the design was based on. The Window Energy Rating Scheme is the industry scheme for comparing window performance, and a substitution that is not documented can undermine the energy assessment for the whole dwelling. Check the label against the schedule at delivery.

How long do I have to raise a defect?

The contract and the relevant legislation set the notice periods, and they differ between supply-only and supply-and-install arrangements. The safe practice is to raise any defect the day you find it, in writing, regardless of the period. Late notice does not just weaken the claim; it often shifts the cost of removal and reinstatement onto you.

Questions builders ask

• Materials
• Quality
• Windows

Published 31 August 2026. General information for builders, not legal, financial or engineering advice for a specific job. Check current requirements with the relevant regulator or standard before relying on them.