Condensation Analysis That Actually Works (Not Just Tick-Box Compliance)
Condensation is one of those building issues that hides in plain sight. It doesn’t make noise, it doesn’t smell (until the mould sets in), and it can quietly destroy a building from the inside out. After 15+ years testing hundreds of homes, we’ve seen perfectly finished walls hiding soggy insulation, rotting framing, and mould colonies thriving in the dark. The truth? Compliance alone won’t keep your building dry.
Why Condensation Management Matters More Than You Think
What Condensation Really Does to Buildings
Condensation happens when warm, moist indoor air meets a cold surface or layer in your building envelope. The result is water where it doesn’t belong — inside walls, roofs, or floors. It might look like a harmless fog on a window, but inside your walls it’s quietly wetting your insulation, swelling your framing, and setting the stage for structural damage.
The Health & Durability Costs Nobody Talks About
Moisture equals mould. And mould isn’t just ugly — it’s a health hazard. It can trigger asthma, allergies, and other respiratory problems. Structurally, moisture drives timber rot and corrosion of metal fixings, reducing the lifespan of your building and driving up maintenance costs.
Why “She’ll Be Right” Isn’t a Moisture Management Strategy
For years, the default solution to condensation risk has been hope. Hope that the building dries out. Hope that ventilation is “good enough.” Hope that the builder did the flashing correctly. Hope is not a strategy — hygrothermal modelling is.
What AIRAH DA07 Actually Says (and Why You Should Care)
The DA07 Moisture Control Scope — in Plain English
AIRAH DA07 is Australia’s moisture-control design guide. It sets clear performance criteria: run a proper hygrothermal model, simulate real climate data, and prove that the mould index stays below 3 on all critical surfaces. Simple idea: if the surface never stays wet long enough, mould won’t grow.
How It Relates to ASHRAE 160 (and Why That Matters)
DA07 is based on ASHRAE 160, the international gold standard for moisture design. This means results are comparable with projects worldwide, and it brings Australian design into line with international best practice.
Key Inputs: Climate, Materials, and Indoor Humidity
DA07 tells you what data to use: real climate files, indoor humidity assumptions (not just “average days”), and material properties. It even recommends starting with wet construction materials because, let’s be honest, most sites get rained on.
Compliance vs. Reality: Where Builders Get Caught Out
Surface Mould Pass ≠ No Condensation Inside Your Walls
Passing the mould index test just means you’ve avoided mould on a specific surface. It doesn’t guarantee that moisture isn’t accumulating inside the insulation or framing. We’ve seen WUFI models that pass DA07 but still show a slow moisture build-up over years — that’s a durability time-bomb.
The Gaps in “Just Meet the NCC” Thinking
The NCC sets a minimum bar, not a performance guarantee. Meeting the code might keep you legal, but it won’t necessarily keep you dry. Real performance depends on buildability, workmanship, and long-term moisture behaviour — none of which get checked at handover.
What We See on Real Projects After 15+ Years Testing
We’ve tested homes that pass every compliance box but still have hidden dampness. The fan goes on, and the infrared camera lights up like a Christmas tree. Compliance is not performance — and finding that out after people move in is a very expensive lesson.
Our Process for Condensation Analysis
Step 1: Define the Assembly and Real-World Conditions
We start with the actual wall, roof, or floor assembly — not the “idealised” spec. Then we define real indoor conditions: heating patterns, ventilation rates, even expected occupancy.
Step 2: Model Moisture Transport with WUFI (Not Crystal Balls)
We use WUFI, the industry-standard hygrothermal modelling tool, to simulate how moisture moves through the assembly under real climate data.
Step 3: Calculate the Mould Index and Check Against DA07
We check that all critical surfaces stay below a mould index of 3, just as DA07 requires.
Step 4: Stress-Test the Design for Wet Years and Worst-Case Use
We push the model harder — think wet construction, cold snaps, or higher-than-normal indoor humidity — to see if the design still holds up.
Step 5: Recommend Fixes Before You Build (Because It’s Cheaper Now)
If the model shows risk, we recommend changes: better membranes, ventilated cavities, or vapour control layers. Fixing it on paper costs a fraction of fixing it after handover.
Common Mistakes We Prevent
Choosing the Wrong Membrane or Putting It on the Wrong Side
Vapour-permeable, vapour-barrier, Class 1, Class 4 — get this wrong and you’re basically building a terrarium.
Forgetting to Ventilate Roof Cavities (Yes, It Still Matters)
Even in the age of airtightness, roof space ventilation is critical in certain climates. It’s cheap insurance against trapped moisture.
Designing for Compliance, Not Performance
If your design just scrapes through NCC compliance, you’re leaving no margin for error. One blocked vent or one wet winter and you’re back to square one.
What Good Looks Like
Examples of Wall & Roof Build-Ups That Work in NZ & AUS Climates
We can show you assemblies we’ve tested that work year-round. These aren’t just theoretical — they’re built and standing.
Case Studies: Homes That Would Have Passed NCC but Failed in Reality
We’ve modelled “compliant” houses that still accumulated moisture. Real-world examples prove why this extra step is worth it.
The Cost of Fixing It After Construction (Spoiler: It Hurts)
Remediation often costs 10x what it would have cost to get the design right in the first place. Builders hate rework; owners hate ripped-out linings. Do it right the first time.
When Not to Use Our Service
Projects That Are Too Far Gone (Remediation Stage)
If the damage is already done and mould is visible, you need remediation specialists, not design modelling.
When You Only Need a Quick NCC Tick-Box (and Don’t Care About Long-Term Risk)
If you just need a certificate to keep a certifier happy, there are cheaper ways to get it. We’re here for clients who want to sleep at night.
Ready to Do This Properly?
When you’re ready to look beyond compliance and design for real-world performance, we’re ready to help. Our condensation analysis will give you clear answers and actionable recommendations — not just a report to file away.
And no, it’s not because your house needs to “breathe.” It’s because your wall build-up wasn’t designed to dry properly. Let’s fix that before the mushrooms move in.
