Holiday house shut up for weeks, vents lost behind a deck, a smell that greets you at the door: under a Forster or Tuncurry floor the air has stopped moving. We reopen and add vents, fit fans to pull the air through, lay a barrier over damp ground and check the timber. Tell us what you have noticed and where the house is.
Get a Quote →Many homes around Forster, Tuncurry and the older parts of Taree stand on a timber floor over a subfloor space, and that space is built to breathe: in through the vents on one wall, across under the floor, out through the vents on the other. Subfloor ventilation is keeping that current of air going, so the moisture that rises off the ground leaves with it instead of settling on the timber.
The Great Lakes and Manning coast sits low and close to the water table, around Old Bar, Pacific Palms and Hallidays Point especially, so the ground under a house here is rarely dry for long. Holiday homes make it worse: shut up for weeks at a time, nothing moves the air inside or under them. Add a deck, a garden bed or an extension over the vents and the damp condenses under the floor, grows mould and, over a few seasons, softens the bearers and joists.
Why we care about it: the worst subfloor we get called to is usually the one with the nicest new deck over it. The owners fixed the outside, sealed the vents without knowing, and found out two winters later when the hallway floor went soft. We would rather get under a house early, while it is a vent job and not a timber job.
On the day we start underneath with a moisture meter and a torch, reading the timber, the soil and every vent. Buried vents come out from behind the paving or the deck edge, rusted grilles are replaced and new openings go in on the side the breeze comes from. A fan sized to the floor goes on the far wall to pull the air across, wired to a switch or humidistat outside. Over ground that stays wet we lay heavy plastic, overlapped and pinned, so the soil stops feeding the damp. Expect brick dust, a bit of noise and a low hum afterwards, and give the timber a few weeks to dry. The chart below shows the way the air should travel.
Multi-fan systems that pull moist air out and push fresh air through, especially valuable for holiday homes left shut up between visits. Cost depends on whether one fan covers the space or the 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 decks 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 sandy subfloor soil, common in low-lying blocks around Old Bar and Hallidays Point. 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, useful before listing a holiday let or buying a coastal property. 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.
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.
When you look matters. March is the wettest month at the Bureau of Meteorology's Forster-Tuncurry station, averaging 152.2 mm, and September the driest at 65.8 mm. Damp soil after a March downpour is worth noting, but a dry September is the sharper test. Soil that stays dark then is more likely to point to moisture coming up from the ground, or a leak, than to the weather.
Two things largely decide how dry a subfloor in Forster-Tuncurry stays: the air moving through the vents and the ground underneath. Bureau of Meteorology records for the Forster-Tuncurry Marine Rescue station, with rainfall records going back to 1896, show mean relative humidity of 76% at 9am and 68% at 3pm (1999-2010) and average rainfall of about 1,220 mm a year. Humid air takes less moisture with it as it passes under a house, so passive vents have less to work with. Winter nights there are mild, with a July mean minimum of 8.7°C (1999-2020), so cold-night condensation is a smaller part of the problem than wet ground.
The ground side depends on where the house sits. The 2012 Wallis Lake foreshore flood study review by WMAWater, listed under MidCoast Council on the NSW Flood Data Portal, allowed for lake floods dominated by ocean levels as well as floods dominated by rain runoff, so a water mark under a foreshore house may not line up with a local downpour. In Tuncurry, Great Lakes Council's 2014 Wallis Lake Estuary and Catchment Management Plan noted historic spear-point access to the Tuncurry aquifer on properties there. Moisture under a Tuncurry floor can come up from below, not just down with the rain.
That is why a vent-only fix doesn't suit every subfloor here. Where the ground is wet, the sensible order is a moisture barrier over exposed soil first, then fans where vents alone can't move enough air.
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 means trenching along the footings, ask first whether the ground is acid sulfate soil. Where less than 10 tonnes of acid sulfate soil is disturbed, MidCoast Council's Acid Sulfate Soil Management Plan for Minor Works (October 2023) applies. Dug material has to be treated with agricultural lime within 48 hours.
This site takes subfloor ventilation enquiries from Forster, Tuncurry, Pacific Palms, Hallidays Point, Old Bar and Taree, plus nearby Great Lakes and Manning Valley suburbs.
Tell us what you need and where the property is.