What Are You Breathing Inside Your Home? How Stllhaus Improves Indoor Air Quality

‍ You go to bed with the bedroom door closed.

For the next eight hours, two people breathe, sleep and release moisture into a room that may have no reliable source of fresh air.

By morning, the room may look exactly as it did the night before. However, carbon dioxide and humidity have increased while you slept. Higher carbon dioxide is a sign that exhaled air is accumulating faster than fresh air is replacing it, while persistent excess moisture creates conditions in which condensation and mould can develop.

The room may simply feel less fresh when you wake, with no obvious explanation for why.

Elsewhere in the house, cooking has released particles and odours. Showers have added water vapour. Furniture, paints, adhesives and cleaning products may release volatile compounds. Outdoor air can bring pollen, smoke and traffic pollution inside.

Most of these changes are invisible, yet together they shape the indoor air quality your family experiences every day. Poor indoor air quality can affect comfort, concentration and respiratory health, while persistent excess moisture can create conditions in which condensation and mould develop.

Stllhaus addresses them through an airtight building envelope combined with continuous mechanical ventilation with heat recovery.

The system operates continuously without relying on occupants to manage it. Windows can still be opened whenever someone wants a breeze or stronger connection with outside. Everyday ventilation continues regardless.

What causes poor indoor air quality in a home?

Indoor air changes throughout the day.

People exhale carbon dioxide and release moisture. Cooking generates particles, moisture and odours. Showers and laundry increase humidity. Paints, adhesives, furniture and cleaning products may release volatile organic compounds (VOCs).

Pollutants can also arrive from outside. Bushfire smoke, vehicle emissions, dust and pollen can enter through windows, doors and gaps in the building envelope.

Australian Government guidance identifies particulate matter, VOCs, mould, carbon dioxide, dust, pollen and outdoor pollution among the factors affecting indoor air quality.

Read Australian Centre for Disease Control: Indoor air quality.

The objective is straightforward: reduce avoidable sources and replace used indoor air reliably.

Good indoor air quality depends on reducing avoidable pollutants and reliably replacing used indoor air with filtered outdoor air.

How does uncontrolled air infiltration affect indoor air quality?

Air leaking into a house through gaps is sometimes treated as ventilation.

The route that air takes matters.

Uncontrolled infiltration can draw outside air through subfloors, roof spaces, wall cavities and construction gaps before it reaches occupied rooms. These concealed spaces can contain accumulated dust, insulation fibres, mould-affected materials and pest contamination. In some buildings they may also contain rodent nests or carcasses.

These cavities were never designed as clean-air pathways.

A Stllhaus airtight envelope limits this uncontrolled infiltration. Ventilation air enters through a known outdoor intake and passes through filters before being distributed through the home.

Ordinary indoor dust still exists because people, clothing, pets and daily life generate particles. What an airtight envelope substantially reduces is the uncontrolled movement of air and contaminants through concealed building cavities. People, clothing, pets and daily activity create particles. Fresh-air supply simply does not depend on leakage through concealed building cavities.

The pathway is known. The air is filtered. The volume is controlled.

Are open windows enough to ventilate a home?

Stllhaus homes have openable windows.

They can bring in a breeze and rapidly purge a room when conditions are suitable. Their limitation is consistency.

Cold winter nights, hot afternoons, heavy rain, traffic noise, bushfire smoke and high pollen can all make opening windows undesirable. People also sleep, leave for work and forget.

Australian Government Your Home guidance recognises mechanical ventilation with heat recovery as a way to provide reliable ventilation in well-sealed homes.

Read Australian Government Your Home: Ventilation and airtightness.

How do airtight homes get fresh air?

Airtightness limits uncontrolled air movement through gaps and poorly sealed junctions. Ventilation intentionally replaces used indoor air through a designed pathway.

Both are resolved together.

A leaky house may experience substantial air movement, although its amount, timing and source remain uncontrolled. An airtight house requires reliable ventilation because carbon dioxide, moisture and pollutants can accumulate when accidental leakage is removed.

CSIRO research into recently completed Australian homes found that improving airtightness reduces draughts and energy use, while airtight homes without adequate controlled ventilation can increase condensation and mould risk.

Read CSIRO: Sealing the comfort of our new homes.

How does mechanical ventilation with heat recovery work?

Each Stllhaus uses mechanical ventilation with heat recovery, commonly called MVHR.

Filtered outdoor air is continuously supplied to bedrooms and living spaces. Used air is extracted from bathrooms, laundries and other areas where moisture and pollutants are generated.

The incoming and outgoing air streams remain separate. Inside the unit, a heat exchanger recovers useful energy from one air stream and transfers it to the other. This reduces energy lost through ventilation and helps maintain more stable indoor conditions.

Ventilation rates, duct routes, intake locations and commissioning are resolved as part of the home.

Most importantly, the system keeps operating without relying on occupants to manage it.

Nobody needs to monitor carbon dioxide, decide when a bedroom requires fresh air or remember to open windows before bed. The MVHR continues supplying and extracting air throughout the day and night.

How do cooking and moisture affect indoor air quality?

Cooking and everyday moisture can materially affect indoor air quality when pollutants and humidity are allowed to accumulate.

Ventilation works best when pollutants are controlled close to where they are created.

Stllhaus homes are all-electric, removing combustion gases associated with gas cooktops. Cooking can still generate fine particles, moisture and odours, so the kitchen strategy captures these emissions close to their source.

Bathrooms and laundries create another challenge. Showers, washing and drying introduce moisture that needs to leave the home.

Continuous extraction helps prevent persistent humidity building up and reduces conditions that support condensation and mould.

Why does filtered ventilation matter for Melbourne pollen and smoke?

Melbourne provides a powerful local example of why control over incoming air matters.

On 21 November 2016, Melbourne experienced the world's largest recorded epidemic thunderstorm asthma event. Victoria's Department of Health describes it as unprecedented in size, severity and impact. The state now operates an epidemic thunderstorm asthma forecasting system during grass pollen season.

Read Victorian Department of Health: Epidemic Thunderstorm Asthma Program.

Bushfire smoke, traffic pollution, dust and seasonal pollen create other periods when bringing outdoor air directly through open windows may be undesirable.

An MVHR passes incoming ventilation air through filters before distributing it through the home.

Filtration cannot eliminate every pollutant or allergen. Doors open and particles are carried indoors on people, pets and belongings. It does give the home's principal ventilation supply a controlled, filtered pathway.

For a home designed around health and wellbeing, that is a meaningful advantage.

How do building materials affect indoor air quality?

Ventilation is only part of indoor air quality.

Some paints, adhesives, engineered products, furnishings and coatings can release VOCs. Australian Government guidance recommends reducing these sources through material and product selection where possible.

Read Australian Centre for Disease Control: Indoor air quality.

Stllhaus considers indoor emissions alongside durability, embodied carbon, maintenance, appearance and long-term performance.

Where a pollutant can reasonably be avoided at source, there is less of it for the ventilation system to remove later.

Does an MVHR require maintenance?

Yes.

Filters collect particles and require periodic replacement. Intakes, outlets and the ventilation unit also need inspection and servicing.

The Stllhaus aftercare program will manage scheduled ventilation maintenance, including filter replacement and servicing required to keep the system operating as intended.

A home designed to last for 100 years needs continuing care. Maintaining the systems that protect its performance is part of that commitment.

What does good indoor air quality feel like?

Often, you notice the consequences rather than the system.

A bedroom receives filtered outdoor air throughout the night with the windows closed. Moisture is extracted while the family showers. Cooking pollutants are managed close to their source. Ventilation continues while everyone sleeps, works or leaves the house closed for the day.

The home does not wait for someone to notice that a room feels stuffy before fresh air arrives.

When pollen is high or bushfire smoke affects outdoor conditions, the principal ventilation supply continues through its filtered pathway.

The family can still open windows because the weather is beautiful, they want to hear the rain or they want a breeze through the house.

The choice remains theirs.

How can indoor air quality affect health and wellbeing?

Poor indoor air quality can affect health, and people with asthma, allergies or other sensitivities may be more susceptible to particular pollutants.

A Stllhaus cannot prevent asthma, cure allergies or guarantee a particular health outcome. Human health is influenced by many interacting factors.

The home can reduce avoidable indoor pollutants, manage moisture, filter incoming ventilation air and continuously replace used air without relying on occupant behaviour.

These are measurable design decisions and one part of the wider healthy-home approach explored in What Makes a Healthy Home? How Design Supports Health and Wellbeing.

How Stllhaus manages indoor air quality

Most people will never see the airtightness layer inside their walls or the ducts moving air through the ceiling.

They should benefit from the thinking behind them every day.

Stllhaus treats indoor air quality as part of the building system from the beginning.

Airtightness controls unintended infiltration. Mechanical ventilation determines where fresh air enters and where used air leaves. Filtration protects the incoming supply. Extraction removes moisture and pollutants close to their source.

The system continues through winter nights, hot afternoons, rain, high pollen and the ordinary changes of family life.

It keeps doing its job without requiring the family to manage it.

You can still open the windows.

You simply do not have to rely on them to breathe well inside your home.