Why Does My House Smell Musty Under the Floor?

Most homeowners recognise that distinct, musty smell the moment they walk through the door. It’s earthy, damp, and faintly sweet — like old timber left out in the rain. In Melbourne’s older suburbs such as Camberwell, Glen Waverley, and Box Hill, that smell often creeps in from under the floor. But what exactly causes it, and what can you do about it?

Understanding Where the Smell Comes From

A musty odour under the house usually starts in the subfloor — the dark, hidden space between the ground and the underside of your floorboards. It’s out of sight, and because it’s rarely checked, it becomes a perfect environment for moisture to linger.

Melbourne’s weather doesn’t help. Long wet winters, followed by humid summer days, create a constant cycle of condensation and dampness. If the air under your home can’t move freely, that trapped moisture mixes with dust and organic materials such as timber and soil. Over time, it releases gases and spores that travel up through your floorboards and into your living spaces.

Some people assume the smell comes from carpets, walls or drains, but in most cases, the culprit is the subfloor cavity itself. Once you know that, the real question becomes — why is there so much moisture down there in the first place?

The Hidden World Beneath Your Home

Every house in Melbourne sits differently on the land. Some are perched on stumps, others have partial basements or concrete slabs. Older weatherboard homes, especially in suburbs like Blackburn and Surrey Hills, often have generous crawl spaces beneath them — remnants of an era when natural airflow was considered enough.

Fast forward several decades, and those same homes have been sealed up tight for energy efficiency. New flooring, added insulation, garden beds pressed against the walls — all of these small changes limit the natural cross-ventilation that used to keep the subfloor dry.

When air stops moving, the ground beneath your home stays damp after rain. Over time, timber stumps, joists, and bearers begin to absorb that moisture. In enclosed spaces, even the smallest leaks or condensation can turn into persistent damp patches. Once mould spores find their way in, they thrive on that trapped humidity.

Common Causes of Musty Subfloors

Several culprits tend to pop up again and again when inspecting Melbourne homes:

• Poor ventilation: The most common issue. Without adequate vents or airflow, humidity lingers like fog under the house.
• Blocked or undersized vents: Overgrown plants, renovations, or insulation often cover vents, reducing natural air exchange.
• Leaking pipes or drainage: Even a slow drip from a bathroom waste or stormwater line can keep the soil damp for months.
• Ground moisture and poor grading: If the land slopes towards the house or water pools near the foundations, that dampness seeps up.
• Condensation: In colder months, warm indoor air meeting the cool subfloor surfaces can cause condensation — a hidden source of moisture.

These problems are rarely visible from inside. But the smell? That’s your early warning sign.

How Electrical Maintenance Plays a Role

It might surprise some homeowners that electricians are often the first to identify subfloor moisture issues. During electrical maintenance, a licensed electrician may crawl under the house to inspect wiring, power points, or junction boxes. That’s when they notice the tell-tale damp air, corrosion on fittings, or signs of mould.

At Kenner Electrics, the team has seen this countless times across Melbourne’s eastern suburbs. While inspecting wiring under homes in places like Mont Albert and Doncaster, they’ve come across soft floor joists, dripping pipes, and even old vents rusted completely shut. In each case, the homeowner had mentioned that lingering “musty” smell inside — unaware of the damp world just beneath their feet.

The Science Behind the Smell

What people describe as “musty” is actually a mix of compounds produced by mould and bacteria breaking down organic matter. When wood, dust, and soil stay damp, microorganisms begin to grow and release volatile organic compounds (VOCs). These gases rise through gaps in the floorboards or ducts, bringing that unmistakable scent into your home.

Unfortunately, it’s not just an unpleasant smell. Prolonged exposure to damp air can also affect indoor air quality. Those same spores and compounds can aggravate allergies, trigger asthma, and worsen sinus issues — especially for children or older adults. That’s why solving the root cause, not just masking the odour, is so important.

Why Subfloor Ventilation Is So Effective

Mechanical subfloor ventilation works by moving air — simple in theory, but powerful in practice. By using quiet inline fans, ducting, and strategically placed vents, the system draws out stale, damp air and replaces it with fresh air from outside.

In Melbourne, where humidity and soil moisture vary dramatically through the seasons, a properly designed system maintains a consistent airflow year-round. It doesn’t just remove the smell; it helps stop the conditions that cause it. Dry timbers, dry soil, and less condensation mean fewer problems over time.

Electricians often connect these systems to smart timers so that the fans operate automatically during the day and switch off at night. That means you won’t hear them running, yet your subfloor keeps breathing while you sleep.

What Happens Without Proper Ventilation

Ignoring the problem can lead to more than an unpleasant odour. Persistent dampness under a home can cause:

• Timber rot: Moisture weakens the structural timbers supporting your floors.
• Mould growth: Mould spores spread through vents and cracks, finding their way onto skirting boards and carpets.
• Electrical corrosion: Damp conditions accelerate rust on metal junction boxes and degrade cable insulation.
• Pest attraction: Termites, silverfish, and even rodents are drawn to moist, dark spaces.

Homeowners in Glen Iris and Hawthorn have shared stories of noticing warped floorboards or a soft, springy feel underfoot long before they saw mould. Once those signs appear, the damage is already well underway.

A Real Example from Melbourne’s North Eastern Suburbs

At a charming period home in Thornbury, Kenner Electrics was called in to solve a long-standing issue with excess moisture under the house. The homeowner had been noticing that familiar musty smell creeping into the living spaces, and her plumber — a close friend — suggested it might be time to take a proper look at the subfloor.

When our team arrived, the first thing we noticed was that moisture had built up over time, and without enough ventilation, it was starting to create the perfect conditions for mould and wood rot. We designed a ventilation system capable of achieving ten full air changes per hour — a rate proven to keep underfloor environments dry and healthy.

To achieve this, we installed two high-performance 150mm centrifugal inline exhaust fans, and a smart timer switch was wired in so the fans could run automatically during the most effective times of day. This allowed the homeowner to enjoy the benefits of a dry, well-ventilated subfloor without having to think about when to turn it on or off.

A few weeks later, the homeowner found the space below the house noticeably drier. She told us that not only had the musty smell disappeared, but even the salt shakers in her pantry had stopped clumping. Sometimes it’s the little things that show just how much difference proper airflow can make.

Will Subfloor Ventilation Make Your Home Colder?

It’s a common worry, especially in Melbourne’s chilly winters. The good news is, subfloor ventilation doesn’t draw air from your living spaces — it circulates air in the cavity below. That means it won’t make your home colder.

In fact, by drying out damp timber and soil, it can help stabilise your indoor temperature. Moisture acts like a cold sponge under your house; remove it, and you often find your home feels warmer and less humid overall.

How Long Does Installation Take?

For most homes, a professional installation takes less than a day. The process begins with a detailed inspection of the subfloor to measure access points, moisture levels, and vent placement. From there, the electricians fit inline fans, run ducting to appropriate outlets, and wire up the system to a power source and timer.

Modern fans are designed to be quiet and low-maintenance. Once installed, they require little more than an occasional check to ensure vents are clear of debris or cobwebs.

What If Your Home Already Has Vents?

Older Melbourne homes often have brick or terracotta vents built into the foundations. While they were effective decades ago, they rely entirely on passive airflow. That’s fine in dry, windy regions — but in the city’s still, damp winters, passive airflow simply isn’t enough.

The Long-Term Benefits

Subfloor ventilation is one of those improvements you don’t see, but you feel. A dry subfloor supports healthier air inside the home, prevents long-term structural damage, and even protects insulation from becoming damp and ineffective.

Homeowners often mention that the “musty smell” vanishes after just a few weeks, replaced by a neutral, clean scent. Over time, you also avoid costly repairs associated with moisture damage — and that peace of mind is worth a lot.

Preventing Moisture Problems in the Future

Ventilation is one part of the solution; prevention is the other. Simple steps can help keep the subfloor dry year-round:

• Keep garden beds, soil, and mulch clear of foundation vents.
• Ensure downpipes and drains direct water away from the house.
• Check for leaking pipes, particularly under bathrooms or kitchens.
• Maintain insulation and ensure it doesn’t block vents.
• Schedule regular inspections during wet seasons.

These small maintenance habits make a big difference. Think of them as the first line of defence against Melbourne’s unpredictable weather.

What can you do about it?

If you’ve noticed a damp or musty smell under your floor, it might be time to take a closer look at your subfloor ventilation. Kenner Electrics can inspect the space, assess airflow, and recommend a safe, long-term solution that suits your home.

For homeowners across Melbourne’s eastern suburbs — from Box Hill and Balwyn to Glen Waverley and beyond — improving subfloor airflow can make all the difference. A little fresh air under your home can mean a lot more comfort inside it.

Contact us today on 9996 0663.