A musty smell in the back rooms, mould low on the walls, carpet that never feels dry: the damp is coming up from under the floor. We dig out buried vents, cut new ones, fit fans where the breeze does not reach, lay a barrier over wet ground and check the bearers and joists while we are there, in Batemans Bay, Batehaven, Moruya and across the Eurobodalla. Tell us what the house is doing.
Get a Quote →Most homes along the Eurobodalla coast, from Batemans Bay down to Narooma, stand on a timber floor with a gap underneath, the subfloor. That gap is meant to breathe: air comes in through vents on one side of the house, moves under the floor and leaves through the other side, carrying the damp off the soil with it. Subfloor ventilation is nothing more than keeping that air moving.
Here it has to work harder than most places. Homes tucked against bush and shaded slopes around Malua Bay and Surf Beach sit on ground that stays damp for long stretches, and the mornings are humid for much of the year. Block the vents with a retaining wall, a garden bed or a deck and the moisture has nowhere to go: it condenses under the floor, grows mould and, given time, softens the bearers and joists that hold the floor up.
We do this work because of what we find when a house has been left too long: a floor that gives a little underfoot near the back door, and a joist under it that a screwdriver goes into. None of that shows from inside until the smell does. So we find where the water is coming from before we fit anything, rather than bolting a fan to a wet problem.
When we come out, we go under first: a moisture meter on the timber, a torch over the soil and piers, and a check of which vents still let air through. Then we clear the covered vents, replace the rusted ones and cut new openings where the breeze arrives. Fans are sized to the floor area and placed to pull air across the middle of the space, with the cable clipped clear of the ground to a switch on an outside wall. Where the soil stays wet, a plastic barrier goes down, overlapped and pinned. The house smells better within weeks, and the meter shows the timber drying before your nose does. The chart below shows the path the air is meant to take.
Multi-fan systems that pull moist air out and push fresh air through, wired to a discreet switch or humidistat. Cost depends on whether one fan covers the space or a larger home needs a full multi-fan system, plus how much wiring and ducting the job involves.
Cutting in new brick or timber vents, replacing corroded coastal vents, and unblocking vents covered by retaining walls, decking or garden beds. Priced per vent, supplied and fitted — a simple swap costs less than cutting a brand new opening.
Heavy-duty polythene sheeting over exposed subfloor soil to stop ground moisture rising into the timber, particularly useful on shaded, high-rainfall blocks around Malua Bay and Surf Beach. Priced per square metre of ground covered, so it scales with the size of the subfloor.
A crawl-through with a moisture meter and torch to check vent coverage, timber condition and mould before it becomes structural. There's usually a modest inspection fee, and many operators credit it back if you go ahead with the work, so it's worth asking when you book.
Prices are a general guide only — your exact quote comes after an under-house look.
There isn't one product called "subfloor ventilation" — there are a few different setups, and which one suits your place depends on how big the space is, how much air already moves through it, and how wet the ground underneath is. Here's what a contractor is choosing between when they get under your house.
No power, no fans — just openings in the base brickwork letting the breeze do the work. It's the cheapest fix, and it's the right one when the house simply hasn't got enough vents or the ones it had have been covered over. It only works if air can get in one side and out the other. If your subfloor is wide, boxed in, or the vents all face the same way, passive on its own usually won't shift it.
One fan pulling damp air out, with the existing vents letting fresh air in behind it. Suits smaller subfloors, or a house where the airflow is nearly there and just needs a nudge. Simplest powered option and the least to go wrong.
Fans pushing fresh air in on one side of the house and pulling stale air out on the other, so the whole space gets swept instead of just the bit near the vent. This is the setup for wider homes where the air in the middle sits still and never dries. Most multi-fan jobs end up being some version of this.
Flexible ducting run to the corners air never reaches — behind a bathroom addition, under an enclosed deck, or wherever piers and walls break the space into pockets. Usually added to a cross-flow system rather than used on its own.
A small solar panel runs the fan instead of mains power, so there's nothing on your electricity bill and often no switchboard work. The neat part is the timing — it runs hardest on hot, bright days, which is exactly when the air is driest and moisture actually evaporates. Some setups add a mains or battery backup to keep going through a run of grey weather.
A plain switch means you have to remember. A timer runs set hours. A humidistat is the set-and-forget option — it starts the fans only when humidity under the house climbs past a set point and stops them when it drops. Worth asking about, because it's the difference between a system you manage and one you forget about.
If you get more than one quote you'll hear different fan types named, and they aren't interchangeable. What suits your place depends mostly on whether the air has to travel down a duct or just move across an open space.
Propeller-style, the type usually fitted straight into a vent opening or through the base wall. They shift a lot of air cheaply, which is what you want across an open subfloor. What they don't do well is push air along a length of ducting — the resistance stops them.
Squirrel-cage style, sat in the ductwork rather than in the wall. They move less air than an axial for the same size, but they'll push it a long way against resistance — so they're the choice when air has to be carried to a far corner or around obstacles. Usually the quieter option too, since the unit sits away from the vent.
Fan and panel supplied as a package, with the panel mounted where it catches sun and the fan under the house. Runs on daylight rather than mains, and no ongoing cost. Sizing matters more here than with mains fans, because output rises and falls with the light.
At the Bureau of Meteorology's Batemans Bay (Catalina Country Club) station, mean relative humidity at 3pm is 61% across the year (1991–2010), well below the 9am figure.
If you want fans doing most of their work in the less humid part of the day, solar runs on daylight, and with mains fans a timer can be set to afternoon hours. Ask whoever quotes which suits your place. The same station records at least 1 mm of rain on about 82 days a year, so if solar appeals, ask how the panel is sized and whether a mains or battery backup is worth adding.
Most people notice it inside the house first and never connect it to what's underneath. Here's what to look for, upstairs and down.
You don't have to crawl under to learn a lot. Get down at a vent with a decent torch on a still morning and look for these.
Tape a square of clear plastic flat onto the soil under the house, sealed on all four edges, and leave it a couple of days. Water forming underneath the plastic means the ground is still giving off moisture and a vapour barrier is likely part of the answer. Water forming on top means the air down there is damp and needs shifting.
Pick your moment for the torch check. Look once on a still morning, then again on a dry afternoon a few days later. If the soil is still dark, the bearers still look wet, or the same musty smell is there both times, that can be a sign the space isn't drying out on its own.
After heavy rain, check the low side of the subfloor as well. Signs that water has actually run through, rather than damp air just sitting there: a silt line or water mark on the piers or base brickwork, leaves and debris packed against one side, or small channels washed into the soil. Note which side the marks are on and how high they reach. It says a lot about where the water is coming from.
Bureau of Meteorology records for its Batemans Bay (Catalina Country Club) station show an average of 860 mm of rain a year (1985–2026) and humid mornings: mean 9am relative humidity is 79% across the year and 85 to 86% from May to July (1991–2010). Winter nights are cold too, with a July mean minimum of 3.6°C (1991–2021). Cold, humid air dries things slowly, so a wet subfloor with too few vents, or vents partly covered, can be slow to dry in the cooler months.
Air is only half of it. Eurobodalla Council's Batemans Bay Urban Creeks Flood Study, prepared by Rhelm, looks at flooding from rainfall, allowing for projected sea-level rise, in seven catchments: Maloneys Lagoon at Maloneys Beach, Long Beach Lagoon at Long Beach, Surfside Creek at Surfside, the Batemans Bay Water Garden, Hanging Rock Creek at Catalina, Joes Creek at Batehaven and Short Beach Creek at Sunshine Bay and Caseys Beach. Council lists the study as adopted. If water gets under the house in heavy rain, deal with that first: vents and fans dry a subfloor, but they don't stop water running into it.
Dealing with it can mean digging a drain or sump. Eurobodalla Council says acid sulfate soils occur in low-lying areas near the coast less than 5 m above mean sea level. Where work is likely to disturb them and triggers clause 6.3 of the Eurobodalla Local Environmental Plan 2012, Council says a qualified environmental scientist must test the soil and a management plan must be prepared before consent is granted.
Fans are sold in hardware stores and plenty of people have a go themselves. Sometimes that works. Here's what a contractor is actually being paid to get right.
Musty smells and mould on the walls don't always come from underneath. A leaking shower waste, a blocked downpipe, a roof leak tracking down a cavity, or rising damp in the brickwork all look much the same from inside. Ventilating a subfloor that was never the problem is money gone.
Two fans mounted the wrong way round will short-circuit — pulling air straight back out the vent beside them and leaving the middle of the house untouched. Where the fans go matters as much as how many there are, and that gets judged by looking at the actual space, not a floor plan.
A fan won't outrun water that keeps arriving. Ground sloping back toward the house, a downpipe emptying beside the footings, a garden bed built up over the vents, or a dripping pipe underneath all need sorting or the damp comes straight back.
Mains-powered fans are electrical work and need a licensed electrician. Solar setups avoid a good deal of that, which is part of why they suit older homes with tight switchboards.
Bearers and joists are what hold your floor up. Ventilation work is cheap next to replacing structural timber, and the gap between those two problems is usually a couple of wet seasons.
Termites want moisture as much as they want timber, and a damp subfloor is an invitation. Anyone going under with a torch and a moisture meter is looking at both at once.
If the fix for your subfloor turns out to include digging — a trench to carry water away, a sump, or regrading ground that slopes back toward the house — read Eurobodalla Council's acid sulfate soils page before the work is booked. Council says works in an acid sulfate soils area may need development consent, depending on the class of the land on its acid sulfate soil maps (Class 1 to 5) and the type of work.
So ask whoever quotes the drainage whether they've checked the acid sulfate soil maps for the property and whether the job needs consent. Where soil testing is required, Council says it should follow the Acid Sulfate Soils Manual and the National Acid Sulfate Soil Guidance 2018, so allow time for that before any digging starts.
Enquiries are welcome from Batemans Bay itself and from Maloneys Beach, Long Beach, Surfside, Catalina, Batehaven, Sunshine Bay and Caseys Beach, plus Surf Beach, Malua Bay, Broulee, Moruya, Narooma and elsewhere in the Eurobodalla.
Tell us what you need and where the property is.