Where negative side sits under Australian standards

The short answer, before the clause numbers

Three propositions, stated plainly, because the rest of the page is detail underneath them.

First, no Australian standard prohibits waterproofing from the dry side. The idea that negative-side work is inherently non-compliant is wrong, and it is usually asserted by people selling excavation.

Second, no Australian standard nominates negative-side injection as the primary waterproofing barrier for a new below-ground structure either. The membrane standards describe systems installed on the positive, wet face, because that is where a designed barrier belongs. Negative side is a remedial technique applied to a structure that already exists and already leaks. Selling it as an equivalent to a designed positive-side system in new work is where the trade gets itself into trouble.

Third, and most usefully, remedial work on an existing building is a different compliance question from new work. The National Construction Code applies to building work, and the degree to which it applies to a repair on an existing building depends on the scope of the work and the approval pathway for that project. That determination belongs to the building certifier, not to the injection contractor. What the injection contractor owes is an accurate description of what the method does and does not achieve, in writing, before the work.

Everything below is the detail behind those three sentences.

What each standard actually governs, and where it bites

The most common failure in Australian waterproofing reports is not a wrong conclusion. It is reaching for the standard the author knows rather than the standard that applies. The table below is the map.

The 1994 tell, and the second tell behind it

Here is a quick way to assess any waterproofing report or contractor website you are handed. Search it for AS 3740.

A surprising number of Australian waterproofing businesses, including some operating in this exact sector, still cite AS 3740-1994. The current edition is AS 3740:2021. Citing a 1994 edition in 2026 tells a certifier or a specifier that the document has been copied forward without anyone opening the standard, and it undermines everything else in the report, including the parts that are correct.

The second tell is subtler and more revealing. AS 3740 is the internal wet area standard. If a report about a leaking basement wall, a car park soffit or a retaining wall rests its compliance argument on AS 3740, the author has reached for the standard they use every day on bathrooms rather than the one that applies to the element in front of them. The correct references for below-ground remedial work are the concrete design standard for crack control and durability, the National Construction Code's water management provisions, the original designer's specification and, where an above-ground external membrane is involved, AS 4654.2.

This is not pedantry. The reason it matters commercially is that a report which cites the wrong standard is a report that cannot be relied upon in a dispute, and a body corporate or a builder discovers that at exactly the moment they need it to hold up.

NCC 2022, NCC 2025, and the consolidation you need to know about

The National Construction Code is mid-transition on precisely this subject, which makes it the easiest thing in this field to get wrong in a written report.

NCC 2022 remains the operative edition in most jurisdictions at the time of writing. NCC 2025 was published for adoption from 1 May 2026, with staged and varied state adoption rather than a single national switch.

The change that matters here is structural. NCC 2025 merges the former Parts F1 and F3 into a consolidated Part F1 dealing with water management, covering surface water, sub-surface water, rising damp and external waterproofing. In other words, the provisions most relevant to below-ground and negative-side work have been moved and renumbered. A clause reference that was correct in a report written last year may point somewhere else in the edition that applies to the project.

There is a useful precedent in how one state has handled the transition for remedial work. New South Wales variations expressly permit a choice between the NCC 2022 Amendment 2 and NCC 2025 waterproofing provisions for remedial work to existing apartment buildings. That is an explicit acknowledgement that applying a brand-new code edition to a repair on an existing building is not always sensible, and it is worth knowing about when arguing an approach with a certifier.

The physics no code provision can fix

Compliance discussion tends to obscure the mechanical reality, so state it first and then everything else follows.

Sealing from the dry side redirects water. It does not remove it. The water table, the saturated backfill and the hydrostatic head are all exactly where they were before the work started. What changes is where the water finds its way out. Seal one crack and you can start a leak three metres away, because water tracks laterally between the membrane and the concrete, and between a structural slab and its topping, and exits at whatever is now the weakest point. This is the single most important thing to put in front of an owner before proceeding, and it is why the crack you can see inside is very often not where the water enters outside.

That has a direct consequence for what can honestly be warranted. Nobody can warrant a below-ground structure watertight by working from the inside. What can be warranted is the specific, listed crack or joint that was sealed. A contractor promising the former is either not thinking about it or is relying on you not to.

The second physical point is about where the seal sits. A negative-side seal on the face of a wall is loaded by the head trying to push it off. A seal keyed into the body of the wall is loaded the other way, with the water pressure pressing it in. That is the entire reason the method drills 13 mm holes at 45 degrees, offset from the crack line by approximately half the element thickness so the hole intersects the crack at mid-depth, to two-thirds or three-quarters of the wall thickness and never through the far face. It is also why glued surface ports on a wet wall are a genuine performance problem rather than a stylistic preference: the stiff surface seal they depend on will not adhere to wet concrete and blows off.

The third point is durability, and it is the one engineers ask about. A negative-side repair leaves the body of the wall wet. AS 3600's cover and durability provisions exist because water and chlorides against reinforcement drive corrosion. Sealing the internal face stops the nuisance and the finishes damage; it does not dry the concrete. On an element with low cover, in a marine or aggressive exposure classification, that is a conversation to have with the structural engineer rather than a detail to leave out of the report.

And the fourth, which is the one that gets missed: bond. Hydrophobic polyurethane injected into a wet crack does not bond adhesively, because the water film acts as a bond breaker. The seal it makes is mechanical, a plug keyed into the crack geometry, not glue. That is a perfectly good outcome, but it is not what most specifications imagine when they write the word adhesion.

The Queensland warranty position: why "no warranty" is void

This is the part of the page that matters most commercially, and it is the part the market gets most wrong.

Statutory warranties for domestic building work in Queensland sit in Schedule 1B of the Queensland Building and Construction Commission Act. Three features of them determine the whole negative-side risk conversation.

They are implied into the contract by the legislation. They do not depend on anyone agreeing to them, and they are not created by a clause in your terms.

They cannot be contracted out of. A clause reading "no warranty is given in respect of negative-side waterproofing" does not do what its author intended. It is not a shield. It is, at best, a piece of writing that will be read out to a tribunal by somebody else's lawyer to demonstrate that you knew the method had a limitation and chose to handle it by disclaimer rather than by advice.

And, critically, the Act contains a defence that turns on written advice. Where the owner instructed that the work be carried out contrary to the contractor's advice, and that advice was given in writing before the work was performed, the contractor has a defence available to it. We are deliberately describing the mechanism rather than citing a subsection number, because the precise provision and its conditions are a matter for legal advice on the actual facts. The structural point is the one to take away: the protection lives in documented prior advice, not in an exclusion clause.

Two qualifications so this is not over-read. First, Schedule 1B concerns domestic building work, and whether a particular body corporate or commercial job falls within that definition is a question for the contract and for the strata manager's or lawyer's advice on the specific scheme. Do not assume it either way. Second, where the work is not domestic building work, there is no statutory backstop at all, and the parties are left with the contract and the general law. That makes the written advice more important on commercial and common property work, not less.

So the honest summary is this. On negative-side work, a contractor cannot disclaim its way out of the limitation of the method. It can only describe the limitation accurately, in writing, before the work, and have that acknowledged.

What the written advice has to contain to be worth anything

Prior written advice is only useful if it does the job. A one-line note saying the method has limitations is not advice; it is a disclaimer wearing a different hat. Below is the structure that advice needs to have, and it is what a committee, a builder or an owner should expect from anyone quoting negative-side work, including us.

The document is issued before the works, signed by the owner or the committee before the works, and dated accordingly. That last detail is not a formality. It is the entire point.

1. IdentificationDate, parties, property address, and the specific element being treated, described precisely enough that a stranger could find it: the western basement wall between grid lines 4 and 7, not simply the basement.
2. What we found and how we established itThe observed defect and the evidence for the diagnosis: moisture readings at marked points, tell-tale readings over 4 to 12 weeks where movement was in question, water testing, ground-penetrating radar scanning, inspection during rain. Findings without evidence are opinions.
3. What we ruled out, and howDrainage checked at the ag line outlet and weep holes, services pressure-tested, condensation considered against the rain correlation, membrane condition assessed, corrosion-driven cracking excluded or identified. This is the section that distinguishes a diagnosis from a guess.
4. Why positive side is not being doneAccess, cost, occupancy, landscaping, adjoining property, heritage constraints. State it as fact rather than preference, so the record shows the owner chose between real options.
5. What the method does and does not achieveIn plain English: this seals the defined cracks and joints listed in the schedule below. It does not remove groundwater, it does not reduce hydrostatic pressure against the structure, and it does not make the structure watertight as a whole.
6. The named consequenceWater that can no longer exit at the sealed location may find a different path and appear elsewhere. That is a new defect at a new location, not a failure of this repair, and it is the direct consequence of sealing from the dry side rather than removing the water.
7. The alternatives, pricedExcavation and positive-side membrane replacement, drained cavity, crystalline or cementitious negative-side tanking, curtain injection, drainage rectification — each with an indicative cost band and duration, so the record shows what the owner declined and on what information.
8. What the owner must maintainSubsoil drainage and outlets, weep holes, planter box outlets, sump and pump, surface falls and downpipe discharge. A sealed wall with a blocked ag line behind it is a wall waiting to leak somewhere else.
9. The scope actually being warrantedListed crack by crack and joint by joint, with linear metres against each. This is what makes a later warranty conversation take minutes instead of months.
10. AcknowledgementSigned and dated by the owner, the committee delegate or the builder, before the works commence. Advice dated the same day as the invoice is not prior advice, and everyone in the room will know it.

When negative side lasts, and when it desiccates

Compliance aside, the practical question owners ask is how long it holds. The answer splits cleanly.

It lasts, effectively for the life of the structure, when the crack is dormant, the resin family suits the moisture regime, the seal is keyed into the wall body rather than sitting on its face, and the drainage behind the wall has been restored rather than ignored. That is a genuine permanent repair and it should be described as one.

It fails, and reasonably predictably, in a handful of identifiable situations. The most important is desiccation shrinkage in hydrophilic resins. Hydrophilic polyurethane holds water as a permanent component of the cured polymer, which is exactly what makes it bond so well to damp concrete and chase leaks into fine paths. If that crack then dries out permanently, because the wall only leaks in a wet summer or because the basement gets dewatered, the entrapped water evaporates and the foam shrinks. In theory it re-swells on re-wetting, commonly quoted at two to four times. In practice a shrunk foam can lose its key in the crack and never fully recover.

This is the point at which we have to be honest about something the industry is not. There is a real, unresolved disagreement here. Some manufacturers argue hydrophilic should always be used for crack injection because of the bond to wet concrete. Others argue hydrophobic should always be used because of dimensional stability through wet and dry cycling. Both positions are commercially motivated. The correct answer is a judgement about the specific crack, and the decisive question is simple: will this crack ever dry out permanently? If yes, avoid hydrophilic. If it stays wet forever, as in a planter box or a tank wall or below the water table, hydrophilic or an acrylate gel is the right family.

The other failure modes are movement, which no foam accommodates indefinitely and no epoxy accommodates at all; salt and fertiliser attack, which is why planter boxes are the hardest environment in this trade; and sealing without drainage, which raises the head and simply relocates the problem.

The alternatives, and where each one is the right call

Negative-side injection is one option among five, and a defensible report presents all of them with costs and durations rather than presenting the one the author sells.

Excavate and replace the positive-side barrier. This is the answer when the external membrane has genuinely reached end of life across an area rather than failing at a defined path. Above ground, that replacement is to AS 4654.1 and AS 4654.2; below ground it follows the designer's specification. It costs several times what injection costs, typically by a factor of three to ten, and it takes the space out of use for weeks rather than days. It is also the only option that puts the barrier back where the design intended it.

Drained cavity. Stop trying to defeat the water and manage it instead: a dimpled sheet against the wall creates a drainage plane behind the lining, water runs down it to a channel and away to a sump. This is the right answer where sealing is impractical, where the wall is porous across a broad area rather than cracked along a line, and where the client can accept a pump as part of the building.

Crystalline or cementitious negative-side tanking. A cement-based system whose active chemistry grows crystals in the pores of the concrete itself rather than forming a surface skin. Routinely applied over injected substrate in lift pits and tanks, and the correct partner to injection where the general seepage is diffuse rather than at a defined path.

Curtain injection. Drill through the wall on a grid, typically 250 to 500 mm in each direction, and inject an acrylate gel into the ground behind to form a continuous barrier between the soil and the structure. The gel's viscosity, commonly quoted at 10 to 50 mPa·s, is essentially that of water, which is what lets it permeate soil where no polyurethane will go. It must be injected at low pressure, roughly 2 to 15 bar, because high pressure hydro-fractures the soil and displaces it instead of permeating it. Two things must be in the scope: a trial panel to establish take per point before anyone quotes a rate, and neighbour notification, because gel can travel into adjacent basements, service trenches and stormwater lines.

Fix the drainage. Blocked or absent subsoil drains, blocked weep holes, missing falls, downpipes discharging at the footing. Cheapest, most permanent, and the correct first step often enough that any report which does not address it is incomplete.

Six rules for writing a report that survives being read by the other side

Whether you are an engineer, a building consultant, a strata manager assembling a defect report, or a contractor issuing prior written advice, these six habits are what separate a document that holds from one that gets picked apart.

• Name the edition and year every time. AS 3740:2021, not AS 3740. AS 3600:2018, and say so, having confirmed which edition the applicable NCC calls up.
• Describe the requirement before you cite the clause. If the clause reference later turns out to belong to a superseded edition, a correctly described requirement still stands on its own.
• Keep product conformity separate from code compliance. EN 1504-5 is a product conformity standard that appears on manufacturers' data sheets, and its F, D and S classifications describe intended function. It is not an Australian code requirement and should never be presented as one.
• Do not cite AS 3740 for anything below ground. It governs internal wet areas. Reaching for it on a basement wall is the most common tell that a report has been assembled rather than written.
• State the evidence for each finding. Moisture readings at marked points, tell-tale readings across a 4 to 12 week temperature and moisture cycle, water testing, radar scanning, observations during rain. A finding with no method behind it is an opinion with a letterhead.
• Record what you could not determine, and why. "The subsoil drain outlet could not be located and its condition is unknown" is a stronger sentence than an assumption, and it is the sentence that protects everyone if the drain turns out to be the cause.

Questions we actually get asked

Does the National Construction Code prohibit waterproofing a basement from the inside?

No. There is no Australian standard or code provision that bans sealing from the dry side, and anyone telling you otherwise is usually selling excavation. What is true is that the membrane standards describe designed barriers installed on the positive, wet face, so negative-side work is a remedial technique applied to an existing structure rather than an equivalent to a designed system in new work. The extent to which the Code applies to a particular repair on an existing building depends on the scope of work and the approval pathway, and that is a determination for the building certifier.

A report we have been given cites AS 3740-1994. Does that actually matter?

Yes, twice over. The current edition is AS 3740:2021, so a 1994 reference has been superseded for decades and signals a document copied forward without anyone opening the standard. The second and larger problem is that AS 3740 governs internal wet areas in the first place. If the report concerns a basement wall, a car park soffit or a retaining wall, the standard being cited does not apply to the element being discussed. Ask the author which edition they read and which clause they are relying on.

Which edition of the NCC applies to our project in Queensland right now?

That has to be confirmed for your specific project rather than assumed, and we will not state a date we have not verified. NCC 2022 remains operative in most jurisdictions at the time of writing, and NCC 2025 was published for adoption from 1 May 2026 with staged and varied state adoption. NCC 2025 also merges the former Parts F1 and F3 into a consolidated Part F1 covering water management, so the clause numbers for exactly this subject have moved. Confirm the edition in force and any Queensland variations before anyone cites a clause in a defect report, a scope of works or a contract.

Can a Queensland contractor exclude the warranty on negative-side work in the contract?

Not effectively. Statutory warranties for domestic building work sit in Schedule 1B of the Queensland Building and Construction Commission Act, they are implied into the contract by the legislation, and they cannot be contracted out of. A clause saying no warranty is given on negative-side waterproofing does not achieve what it appears to. The mechanism that does provide protection is different: the Act makes a defence available where the owner instructed that work be carried out contrary to the contractor's advice, where that advice was given in writing before the work. Documented prior advice, not an exclusion clause.

Is a 0.3 mm crack in a basement wall a defect?

Not automatically. AS 3600 carries serviceability crack width limits broadly in the 0.1 to 0.4 mm range depending on the element type and the exposure classification, so fine cracking is designed for rather than exceptional. The relevant questions are whether water is passing through it, whether it is widening over time, and what the exposure classification is for that element. A 0.3 mm crack in a dry internal wall is within design expectation. The same crack passing water into a basement is a durability problem, because water against reinforcement drives corrosion, which is far more expensive to deal with later.

Does injection resin need WaterMark or AS/NZS 4020 certification?

It depends entirely on whether the product will contact drinking water. For a basement wall or a car park joint, no. For a potable water tank, every product touching the water — resin, mortar, sealant, coating — needs current AS/NZS 4020:2018 test evidence, and that is also the basis for WaterMark certification. Test reports carry five-year validity, so obtain the current certificate for the specific product rather than a general assurance from a supplier's representative. Get the certificate before the product arrives on site, not after.

Our engineer specified positive-side membrane replacement and the committee cannot afford it. Is proceeding with injection non-compliant?

It is not automatically non-compliant, but it is a decision that has to be documented rather than quietly made. The correct sequence is: the contractor issues written advice before works setting out what injection does and does not achieve, why the positive-side option is not being taken, the indicative cost and duration of the alternatives declined, and the named consequence that water may find a different path. The committee acknowledges it in writing, dated before commencement. That way the record shows an informed decision between real options rather than a repair sold as an equivalent to the one the engineer specified. If the engineer's specification forms part of a defect claim or an approval, get the engineer's written position on the substitution too.

Where to next

• negative side waterproofing, and when it is the wrong answer
• leaking basements and below-ground walls
• scope it properly before you tender
• the hydrophilic versus hydrophobic argument, unsettled
• our warranty in full, including the exclusions