Australian Home Retrofit Guide: Fix Mould, Cut Energy Bills & Improve Indoor Air Quality

11 Feb

Quick Takeaways:

Deep retrofits reduce energy use by 75-90%, saving $1,500-3,000 annually on bills
Around 50% of Australian homes report dampness or mould issues
Existing homes account for 70% of housing stock through 2050—retrofit beats rebuild
The MIST Method addresses moisture, indoor air quality, systems, and thermal performance

Most conversations about "net zero by 2050" feel abstract when you're trying to decide what to do with your own Australian home. Climate targets and NatHERS star ratings don't help families planning a home retrofit. What makes a real difference are improvements you can feel every day: stable temperatures, clean indoor air quality, lower energy bills, and a home that stays comfortable as Australia's climate becomes more extreme

Home retrofit projects—especially deep retrofits—offer a practical path forward. Instead of chasing distant carbon reduction targets, successful retrofits focus on health, comfort, and resilience first. When homes maintain steady temperatures, eliminate drafts, and provide filtered fresh air, major energy savings and emissions reductions follow naturally.

This guide explains how to transform leaky, mouldy Australian homes into healthy, low-energy spaces through proven retrofit strategies. Whether you're considering a whole-of-house renovation or targeted energy efficiency upgrades, understanding the difference between standard renovations and performance-driven retrofits will help you make better decisions for your home and family.

The Australian Housing Crisis: A Multi-Pronged Solution

Australia faces a unique housing challenge. Most households contain just 1-2 people, yet our housing stock consists mainly of oversized 3-4 bedroom detached homes designed for 1950s-style nuclear families. This mismatch means homeowners pay to heat, cool, and maintain far more space than they actually use, resulting in unnecessary energy waste and higher carbon emissions

Three strategies to address housing affordability and sustainability:

Retrofit existing homes – Around 70% of buildings Australians will occupy by 2050 already exist today, making home retrofits essential for rapid decarbonisation

Build better new homes – Focus on climate-specific, energy-efficient designs rather than repeating the mistakes of existing housing stock

Add gentle density – Introduce small second dwellings and missing-middle housing near jobs, services, and public transport

Home retrofit sits at the centre of this strategy because it works with existing building stock instead of demolishing and rebuilding from scratch.

Why Home Retrofit Beats Rebuild: The Numbers

Demolishing and rebuilding Australian homes at scale isn't realistic or sustainable. Deep retrofits offer the most plausible pathway to decarbonise housing quickly while avoiding the massive embodied carbon footprint of new construction. Studies show that replacing an existing building generates roughly double the embodied emissions of retrofitting it.

Performance outcomes from typical deep retrofits:

EnerPHit retrofits achieve 75-90% reduction in energy demand for heating reference
EnerPHit retrofits reduce operational carbon emissions by up to 94% reference
Bill savings: typically range from $1,500-3,000 annually for typical single-family home EnerPHit retrofits reference
Comfort improvement: Year-round indoor temperatures maintained between 20-25°C with no drafts or cold spots.

By comparison, CSIRO research found that new Australian homes average about 15 air changes per hour at 50 Pa—meaning the entire volume of indoor air leaks out 15 times every hour through gaps and cracks. This energy-bleeding problem is built into how we currently construct homes. reference.

Health Benefits of Home Retrofits: Addressing Mould and Indoor Air Quality

Health and comfort should drive residential design decisions, yet many Australian homes fail at basic requirements like keeping occupants warm, healthy, and breathing clean air. National survey research reveals that approximately 50% of Australian households report dampness or mould in their homes, with roughly one-third reporting visible mould growth—consistent with international findings showing similar rates across many countries. reference

This isn't merely a cosmetic issue. Widespread mould and dampness reflect fundamental building science failures that affect respiratory health, productivity, and the ability of vulnerable residents to safely remain in their homes as Australia's climate becomes wetter and more extreme.

Common health issues from poor home performance:

Respiratory problems from mould spores and poor ventilation
Temperature-related stress from inadequate insulation
Indoor air pollution from unfiltered ventilation
Condensation and moisture damage accelerating building deterioration

Proper home retrofits address these health hazards by controlling moisture, providing filtered fresh air, and maintaining stable temperatures—creating genuinely healthy indoor environments.

Understanding Retrofit vs Renovation: What's the Difference?

A retrofit is a performance-driven upgrade that keeps the main building structure while improving energy efficiency, comfort, health, durability, and sometimes safety. A deep retrofit (or whole-of-house retrofit) goes further, transforming building performance to near-new-build standards while preserving the existing structure. A renovation focuses mainly on aesthetics and layout with performance improvements as afterthoughts

The MIST Method: Four Pillars of Home Retrofit Success

At Altereco Design, we use the MIST Method to guide home retrofit projects in Victoria and across Australia. These four invisible pillars determine whether a home is truly liveable, energy-efficient, and healthy

M – Moisture Management

If a building can't handle water, nothing else matters. Effective moisture management includes controlling rain penetration, creating proper drying pathways in wall assemblies, managing condensation risk, and preventing mould through smart vapour control and drainage details

I – Indoor Air Quality

Because we continuously breathe indoor air, good IAQ requires controlled mechanical ventilation, filtration systems for bushfire smoke and urban pollutants, and ensuring fresh air reaches bedrooms and living spaces rather than relying on random air leakage

S – Systems

Once the building fabric performs well, right-sized systems like efficient heat pumps, solar hot water, and simple controls can maximize comfort while minimizing energy bills.

T – Thermal Envelope

The building shell—including insulation, high-performance windows, and airtightness—keeps heat where you want it, eliminates drafts, manages thermal bridges, and stabilises indoor temperatures during heatwaves and cold snaps.

Building Science: Why Details Matter in Retrofit Projects

Effective home retrofit is not simply "adding more insulation." Building assemblies must simultaneously manage vapour movement, air leakage, and heat transfer—or you risk condensation, mould growth, and accelerated material deterioration.

Critical building science principles for Australian retrofits:

Airtightness control – Seal unintentional gaps while providing controlled mechanical ventilation
Vapour management – Allow assemblies to dry in the appropriate direction based on climate zone
Thermal bridging – Address heat loss pathways through framing and connections
Fresh air provision – Supply the right amount of filtered, tempered fresh air rather than relying on uncontrolled leakage

Getting these details wrong can make performance worse, which is why working with experienced building designers and architects who understand building physics is essential for successful retrofit outcomes.

Claire Thomas