The rules governing external concrete drainage and grading in Western Australia have changed, and quoting a job without knowing exactly what shifted could cost you far more than the contract is worth. The National Construction Code 2025 introduces mandatory Deemed-to-Satisfy provisions that rewrite minimum standards for falls, step downs, hob heights and structural substrate materials on external concrete areas. For concrete contractors Perth businesses are already operating in a competitive market, but NCC 2025 adds a compliance layer that cannot be ignored when scoping or pricing new work in 2026.
This post breaks down every critical change you need to understand before a single quote leaves your desk. You will learn how to verify WA’s specific commencement date, confirm the new 1:80 minimum fall requirement, meet the 70mm step down and integral hob provision, identify approved structural substrate materials, and recognise when a Performance Solution is required instead of a DTS pathway. A practical pre-quote compliance checklist ties it all together. Whether you are managing residential slabs, commercial paving or earthworks preparation, what follows gives you the technical grounding to price confidently and build to the new standard.
Why NCC 2025 Changes the Rules for WA Concrete Contractors
NCC 2025 introduces mandatory new Deemed-to-Satisfy provisions for external concrete drainage and grading that replace the guidance WA concrete contractors have been quoting against for years. These are not advisory updates; they are enforceable DTS requirements that apply to external slabs, balconies, podiums, and covered outdoor areas.
The changes cut across four interconnected areas: design, construction sequencing, waterproofing detailing, and drainage specification. A job scoped under pre-2025 standards can be non-compliant before the first pour, because the non-compliance sits in the design assumptions your quote is built on, not just the finished work.
The code itself has also been restructured under Part F1 Water Management. Contractors should verify current section numbers against the NCC 2025 online portal rather than relying on previous code editions.
Liability follows the work. Where defects, water ingress, or remediation arise from non-compliant drainage and grading, the exposure sits with the party who quoted and built to an insufficient standard. For concrete contractors in Perth WA operating on residential and commercial sites, that is a direct commercial risk, not a theoretical one.
Because WA sets its own adoption date, confirm it before any other compliance step.
Step 1: Verify the WA Commencement Date Before Anything Else
That commencement timeline point from the previous section is the one to act on first, before any other compliance check makes sense.
NCC 2025 is published nationally, but adoption is determined by each state and territory independently. The ABCB maintains a dedicated state and territory adoption page confirming this. Western Australia sets its own mandatory commencement date, and that date does not default to the national publication date. If you are quoting external concrete work in WA, only the WA adoption date is relevant.
The split-risk problem is real and specific. Win a job quoted under pre-2025 standards, then start construction after the WA commencement date, and the construction phase falls under the new DTS provisions regardless of what was priced. That gap sits with the contractor.
The verification step itself takes minutes. Check the Building Commission WA for the confirmed NCC 2025 adoption date, record it, and attach it to the project file before the quote goes out. This creates a dated record that supports your pricing basis if a compliance question arises later.
Staged and long-lead projects carry an additional layer of risk. A structural slab poured before commencement under the previous provisions may be followed by drainage works that commence after the adoption date, placing that later phase under NCC 2025. The two phases of the same job can operate under different code requirements.
Perth concrete contractors working on multi-stage residential or commercial sites should note this sequencing risk explicitly in their pre-quote checklist and raise it with the certifier or building surveyor before pricing is finalised.
Step 2: Confirm the 1:80 Minimum Fall in the Structural Substrate
Once the WA commencement date is confirmed, the next check is the one most likely to create a quoting conflict.
NCC 2025 provision F1D4 mandates a minimum 1:80 fall in the structural substrate for all external concrete drainage areas. That distinction matters: the fall must be present in the structural layer itself. It cannot be achieved through a tile bed, screed, or topping applied over a flat slab.
This is a direct departure from common site practice. Many contractors have historically formed a flat structural substrate and used a screed to direct water to outlets. Under NCC 2025, that approach no longer satisfies the DTS pathway. The F1D4 Notes explicitly exclude screeds and toppings from counting as structural substrate, with a narrow exception only for planter boxes.
The required fall must also connect to a drainage system compliant with AS/NZS 3500.3-2021. This means drainage outlet locations and system design must be resolved before the substrate is formed, not after the pour when positions are fixed.
For concrete contractors in Perth quoting balconies, driveways, podiums, or covered outdoor slabs, this changes the formwork sequence. The fall must be engineered into the structural pour, which affects falsework setup, pour sequencing, and forming costs.
The practical quoting implication: before finalising any price, check the structural engineer’s drawings for a confirmed 1:80 fall in the substrate. If the drawings show a flat structural slab with a screed overlay handling drainage, the design does not meet DTS. Raise it with the designer before the quote goes out, not after the contract is signed.
Step 3: Check the 70mm Step Down and Integral Hob Requirement
Once the structural fall is confirmed in the drawings, the next check is vertical: the height relationship between the internal floor and the external slab.
NCC 2025 requires a minimum 70mm step down from the internal floor level to all external concrete areas. This differential prevents water from tracking back through the building envelope at threshold junctions, and it is not negotiable under the DTS pathway.
Alongside the step down, a minimum 70mm high integral hob is required around the perimeter of external concrete areas.
Retrofitting is not a viable fallback. Adding a 70mm hob to an existing slab typically creates opening height conflicts that cannot be resolved without broader structural changes. This makes the hob a design-stage item that must be scoped and priced from the outset, not a remedial fix to be resolved after practical completion.
For Perth concrete contractors pricing renovations, extensions, or any work connecting new external concrete to an existing internal floor level, the height differential must be verified before the quote leaves your desk. Where DTS compliance cannot be achieved, a Performance Solution will be required, see Step 5 for how to identify that trigger.
At quoting stage: record the internal floor level, confirm the proposed external slab level, and verify the 70mm clearance with the project designer in writing before issuing a price. Finding this conflict after the contract is signed is a direct path to scope creep and margin loss.
Step 4: Verify Structural Substrate Materials Meet NCC 2025 Restrictions
Once hob dimensions are confirmed, turn to the substrate material itself. NCC 2025 restricts the structural substrate for external concrete areas to exactly two compliant options: concrete conforming to AS 3600, or fibre cement sheeting conforming to AS 2908.2. No other substrate material satisfies the DTS pathway.
This matters at quoting stage because architects and builders sometimes specify alternative substrate systems, particularly on balconies, podiums, or lightweight decking details. If the specified substrate does not meet AS 3600 or AS 2908.2, the entire drainage and grading DTS pathway is unavailable, regardless of how well every other requirement is met.
What to check on the structural drawings:
- Identify the nominated substrate material in the structural specification
- Cross-reference it against the two permitted options
- If an alternative material is specified, raise it with the designer before pricing. Substitution or a Performance Solution will alter both scope and cost, and neither should be absorbed silently into a fixed-price quote
This restriction connects directly to the screed exclusion in Step 2.
Concrete suppliers in Perth providing materials for external slab work should note this as well. Where a project relies on a non-structural topping system to achieve the required falls, a compliance conflict exists that reaches beyond the concreting contractor and affects the full supply chain, including material supply and certification sign-off.
Step 5: Know When DTS Will Not Work and a Performance Solution Is Required
Material non-compliance is one trigger for a Performance Solution. Existing site conditions are another, and this is where remedial and retrofit projects carry distinct risk.
For existing structures, achieving DTS compliance is generally not possible in remedial work. An existing slab formed flat cannot have its structural fall retrofitted because screeds are precluded as structural substrates. An existing doorway with insufficient height differential cannot accommodate a 70mm integral hob without introducing further non-conformances, including balustrade heights and minimum door opening heights. These are common conditions on renovation and extension sites across Perth, not edge cases.
When DTS compliance is not achievable, the project must follow a Performance Solution pathway. That pathway requires a suitably qualified person to demonstrate that the alternative approach achieves the same performance outcomes as the DTS provisions. The contractor does not prepare the Performance Solution, but the contractor is responsible for identifying the trigger.
At quoting stage, flag any of the following as a potential Performance Solution trigger:
- Existing substrate that cannot be reformed to achieve 1:80 fall
- Opening height constraints that prevent a 70mm step down or integral hob
- Structural elements that fix slab levels and prevent compliant geometry
Quoting remedial or extension work under DTS pricing when the site makes DTS unachievable creates a scope gap. That gap surfaces at certification, and if it was not identified before the quote was issued, the cost of resolving it sits with the contractor.
Knowing when to raise a Performance Solution conversation with the certifier, rather than knowing how to prepare one, is a practical quoting skill that directly protects your margin on any existing-structure job.
Your Pre-Quote Compliance Checklist for NCC 2025 Drainage and Grading
Run through the preceding five steps and you have everything you need to build a standing checklist. Use the items below on every external concrete quote before a price leaves your desk.
- Confirm the WA NCC 2025 commencement date. Check the Building Commission WA or the ABCB state adoption page, record the confirmed date, and attach it to the project file. Do not issue a quote for 2026 external concrete work without this documented.
- Check structural drawings for a confirmed 1:80 fall in the structural substrate. If the drawings show a flat substrate with drainage achieved via screed or topping, the design does not meet DTS. Raise it with the designer before pricing.
- Verify the drainage system specification. Confirm it references AS/NZS 3500.3-2021 and that all drainage outlet locations align with the fall direction shown in the structural drawings. A drainage outlet positioned against the substrate fall creates a non-compliance that cannot be resolved on site.
- Confirm the internal floor to external slab level differential. Both the 70mm step down and the 70mm integral hob must be structurally achievable. Measure or confirm this from the drawings at quoting stage; flag any shortfall to the designer before issuing a price.
- Confirm substrate material. The structural substrate must be concrete to AS 3600 or fibre cement sheeting to AS 2908.2. If an alternative is specified, raise it with the certifier and factor resolution costs into the quote scope before pricing.
- Remedial and retrofit jobs: assess DTS achievability first. If any of the four requirements, the fall, the hob, the step down, or the substrate material, cannot be met on the existing structure, note Performance Solution as a likely requirement in your quote scope notes before the job is priced.
Get Your Quoting Process Right Before NCC 2025 Catches You Out
The checklist in the previous section gives you the verification steps. This closing note is about what those steps collectively mean for how you run your quoting process going forward.
The four DTS provisions covered in Steps 2 through 4 are not design-phase details, each one directly shapes what you price and what you build.
The WA commencement date is the threshold question. Until you have confirmed and recorded it, the other checks have no trigger point. Confirm it first, attach it to every project file, and treat it as a standing task rather than a one-off lookup.
Remedial and retrofit jobs carry heightened Performance Solution risk, flag that early, as Step 5 details.
If the structural drawings cannot answer the four verification questions, that gap is itself the finding. Raise it with the designer or certifier before signing anything. Discovering non-compliance after contract execution puts the resolution cost squarely on your business.
Build the checklist into your standard process so that no external concrete job leaves your desk unverified.
Conclusion
NCC 2025 does not leave room for assumptions. Four DTS provisions, one confirmed commencement date, and a clear process for identifying when a Performance Solution is required: these are the foundations of every compliant external concrete quote in WA.
The businesses that get this right early will protect their margins, avoid costly post-contract disputes, and build a reputation for technical accuracy that sets them apart from competitors still catching up.
The businesses that treat compliance as someone else’s problem will absorb the cost when it surfaces later, and it will surface.
Your action today is straightforward. Download the pre-quote checklist, build it into your standard workflow, and confirm the WA commencement date on every active project in your pipeline. One structured process, applied consistently, is all that stands between compliance confidence and unnecessary risk.
Frequently Asked Questions
When does NCC 2025 come into effect for external concrete work in Western Australia?
NCC 2025 is published nationally, but Western Australia sets its own mandatory commencement date independently. The adoption date is not the national publication date. You must check the Building Commission WA or the ABCB state adoption page to confirm the exact commencement date for WA before quoting any external concrete work. This date is critical because work commenced after this date must comply with the new DTS provisions, regardless of when the contract was signed.
What is the key difference between the 1:80 structural fall requirement and using a screed for drainage?
Under NCC 2025, the 1:80 fall must be engineered into the structural substrate itself—it cannot be achieved through a screed, tile bed, or topping applied over a flat slab. The NCC 2025 Notes explicitly exclude screeds and toppings from counting as structural substrate, with a narrow exception only for planter boxes. This means the fall must be built into the formwork and structural pour, affecting falsework setup, pour sequencing, and forming costs.
What are the only two structural substrate materials that comply with NCC 2025?
NCC 2025 restricts the structural substrate for external concrete areas to exactly two compliant options: concrete conforming to AS 3600, or fibre cement sheeting conforming to AS 2908.2. No other substrate material satisfies the DTS pathway. If an alternative substrate is specified in the structural drawings, you must raise it with the designer before pricing, as substitution or a Performance Solution will alter both scope and cost.
Why is a Performance Solution needed for remedial and retrofit projects?
Existing structures often cannot achieve DTS compliance because: an existing flat slab cannot have its structural fall retrofitted (screeds are not permitted as structural substrates), existing doorways may have insufficient height for a 70mm integral hob without creating balustrade or door opening conflicts, and fixed structural elements may prevent compliant geometry. When DTS compliance is unachievable, a suitably qualified person must demonstrate that the alternative approach achieves the same performance outcomes. As the contractor, you must identify this trigger at quoting stage to avoid absorbing resolution costs later.
What is the 70mm step down and integral hob requirement, and why can't it be retrofitted?
NCC 2025 requires a minimum 70mm step down from the internal floor level to all external concrete areas, plus a minimum 70mm high integral hob around the perimeter. This prevents water from tracking back through the building envelope at threshold junctions. Retrofitting a 70mm hob to an existing slab typically creates opening height conflicts that cannot be resolved without broader structural changes, making it a design-stage item that must be scoped and priced from the outset, not a remedial fix after practical completion.