Subfloor Repair Services QLD 2026 - Pricing Guide - Get Quotes

What Subfloor Repairs and Ventilation Cost in Queensland

Under every timber-floored house in this state there is a space that quietly generates a long list of expensive problems while nobody goes near it. It is dark, awkward to enter, and it reports its troubles somewhere else entirely: a musty bedroom, a floorboard that gives underfoot, a door that has stopped shutting, a cornice line that has opened. The owner who finally crawls in with a torch is usually arriving after the repair has grown. Everything here is cheaper the earlier it happens. A smell investigated this year is a different bill from the same smell investigated in five.

Taking the rates first, a proper subfloor inspection with photographs costs $280 to $650 and is the single best value purchase in this part of the house. Cutting in passive wall vents runs $120 to $280 for each vent through masonry and $80 to $180 through timber. A ground vapour barrier laid across the soil is $18 to $40 the square metre. A single ducted extraction fan sits at $650 to $1,600 and a multi-fan humidistat system at $1,800 to $4,500. None of those figures is the kind of number owners brace for.

Structural work is where the larger numbers live. Replacing a bearer costs $180 to $450 for each metre and a joist $220 to $550 each. Sistering a joist alongside a damaged one is $120 to $300. Replacing an individual stump runs $350 to $900, while restumping a whole house reaches $12,000 to $35,000. Propping and levelling a sagging section of floor sits at $800 to $2,500.

Three things make subfloors behave differently in this state. Humidity is the first, because the dew point is reached under a Queensland house far more commonly than under a southern one, and air that cannot escape deposits its moisture on the coolest surface it can find. Termite pressure is the second, the highest in the country, and a damp subfloor is both an attractant and a concealment. Rainfall intensity is the third, delivering water faster than most sites can shed it. All three work together instead of in turn.

There is a fourth factor almost unique to Queensland housing, which is the build-in. Enclosing the space under a highset house to create rooms, a garage, a laundry or a rumpus is close to a cultural practice here, and a great many of those conversions blocked the original ventilation without replacing it. The house above then sits over a sealed, humid cavity for the next thirty years and nobody connects the two facts. It is the single most common cause of subfloor trouble in this state, and almost nobody makes the link. The build-in and the musty bedroom are rarely discussed in the same conversation.

The number that governs almost everything down there is the moisture content of the timber. Below roughly fifteen percent, decay fungi cannot establish and the timber is stable. Above about twenty percent, rot becomes possible and termites find the conditions considerably more inviting. Every intervention in this guide, from a vent to a vapour barrier to a drain, exists to hold that number down, and the ones that attack the source work better than the ones that move air around. Keep that hierarchy in mind reading the rate table.

What follows works through reading the symptoms from inside the house, the component rates, the ventilation requirements and the cross-flow rule nobody applies, dealing with moisture at its source, timber decay and how to tell rot from borers from termites, structural repairs to stumps, bearers and joists, built-in subfloors and flood recovery, regional pricing, and the questions to ask before accepting a quote. Where this forms part of a larger job, the broader renovation services pricing covers the trades working alongside it.

Reading the Symptoms From Inside the House

Most subfloor problems announce themselves upstairs long before anybody crawls underneath, and learning to read those signals is what turns a vague worry into a specific question for a contractor. The useful ones cost nothing to observe and several of them can be checked in an afternoon.

Smell is the first and the most reliable. A persistent musty or earthy odour in a room, strongest near the floor, strongest in the morning, and worse after rain, is subfloor air finding its way up through gaps around pipes, in skirting lines and through floorboards. Air pressure differences pull it upward, particularly when an exhaust fan or a range hood is running, so a house that smells worse while the bathroom fan is on is telling you where the air is coming from. Note which rooms and which conditions, because that detail narrows the search considerably. A smell confined to one corner of the house usually has a cause in the same corner.

Floor movement is the second and it comes in distinct flavours. A springy or bouncy area means a joist has lost section or a bearer has deflected. A single board that moves underfoot is usually a fixing or a localised problem. A floor that has dropped away from the skirting along one wall, leaving a visible gap, means a bearer or a stump line has settled. And a floor that creaks seasonally is regularly just timber moving with humidity.

Doors and windows carry the same information in a different form. Doors that bind on one corner, windows that have stopped latching, and architraves that have opened at the mitres all indicate the frames have racked, and on a timber-floored house the racking usually comes up from below. Where several doors in the same part of the house have gone out together, the cause is structural in place of seasonal. A single sticking door in February is usually nothing more than humidity in the timber. Several doors going out together over a year or two is a different matter.

Visible decay inside the house is less common but conclusive. Floorboards that have cupped or buckled, boards that feel soft underfoot near a wet area, discolouration appearing in a line along a joist position, or paint lifting from the bottom of a skirting board all mean moisture is coming from underneath. In a bathroom, a laundry or a kitchen, the first suspicion should be a leak, with the subfloor second. Damage confined to one area points at a source confined to the same area. A problem spread across the whole floor has a cause spread across the whole subfloor.

Pests belong on the list because the subfloor is how they get in. Rodent noise under the floor, ants trailing from a skirting line, and the mud leads of termites appearing on a wall or an architrave are all subfloor matters. A termite lead on a skirting board means the colony has already come up through the subfloor, and a termite inspection is the immediate call and not a builder. Leave the lead undisturbed so the inspector can see what you saw. Photograph it first in case it is knocked in the meantime.

Condensation and mould in the rooms above complete the picture. Mould appearing on the inside face of external walls at floor level, on the back of furniture against an external wall, or inside built-in cupboards on an outside wall is typically a moisture-load problem, and a wet subfloor is a very common source. Where mould is already established, mould remediation treats the symptom while the subfloor work treats the cause. Doing the first without the second guarantees a return visit, usually within a year. Remediation contractors will generally tell you as much themselves before quoting.

The outside walk is the other half and it takes ten minutes. Walk the full perimeter looking for vents, noting where they are and whether anything blocks them, and check whether the ground outside falls towards or away from the house. Look at every downpipe and work out where the water goes. Note any paving, garden bed, deck, path or addition built against the wall since the house went up, because each one is a candidate for having closed a vent. Compare what you find against the original house plan where you have one.

What all of that produces is a short written list and a handful of photographs, which is exactly what lets a contractor quote a scope, not an investigation. An owner who can say the smell is worst in the south-east bedroom after rain, that two vents are buried behind a garden bed, and that the floor has dropped eight millimetres along the back wall has done most of the diagnostic work already.

Subfloor Repair and Ventilation Rates

Set out below are the lines a straightforward quote should itemise, with a note on what each one addresses. Pricing below is for a south east Queensland job where the crawl space can reasonably be worked in. The ordering is deliberate, because the investigation and moisture-source items near the top are what make the structural items further down either unnecessary or permanent. Read the table from the top down and work in that order. The sequence of works is itself the advice being given here.

The order of that table is the argument. Inspection, clearing, vents, a vapour barrier and drainage together routinely come to less than two thousand dollars, and on a great many Queensland houses they resolve the problem permanently. Fans, structural replacement and treatments sit below them because they are either consequences of leaving the moisture in place or responses to damage it has already caused. Buying from the bottom of the list first is how owners spend ten thousand dollars and still have a damp subfloor. The order is not a preference; it is the whole argument.

Two items go missing from most quotes and both matter here. The vapour barrier is the first, because the soil is usually the largest single source of moisture under a Queensland house and a sheet of plastic across it is remarkably cheap against what it achieves. Debris clearing is the second, since stored timber, old building material, cardboard and garden waste under a house hold moisture, block airflow and give termites both food and cover. Clearing it out is the cheapest useful thing anybody can do under a house, and on a hoarded subfloor it sometimes produces a measurable drop in humidity by itself. Neither item appears in a quote unless somebody asks.

Where the money concentrates is almost entirely about clearance. A subfloor with 900 millimetres of headroom is a workable space where a tradesperson can move, carry material and work at a reasonable rate. The same job in 400 millimetres of crawl space can take twice the hours, and below that it stops being viable at all without excavation. The height under the house is therefore the first question any contractor will ask and the single biggest driver of the quote. Measure the clearance at several points before you ring anybody at all.

Sequencing saves more than negotiating does, and the order is consistent. Deal with external water first, meaning gutters, downpipes and ground falls. Then clear the space and restore cross-flow ventilation. Then lay the vapour barrier across the exposed soil. Then let the subfloor dry for a season and measure the timber again. Only then decide what structural work is genuinely needed, because timber that has been drying for six months reads very differently from timber measured in a wet subfloor.

The Ventilation Numbers and the Cross-Flow Rule

Subfloor ventilation is governed by requirements that are specific and checkable, which makes this one of the few parts of a house an owner can audit against a standard with a tape measure and a calculator. The requirements sit in the National Construction Code, administered by the Australian Building Codes Board, with the timber framing provisions in AS 1684 available through Standards Australia.

The headline figure is an area of unobstructed ventilation opening for every metre of external wall enclosing the subfloor, expressed in square millimetres per metre. What matters practically is that it is an area of open hole and not a count of vents, and that the published figure refers to free area after any grille, mesh or insect screen is taken into account. A decorative vent with a fine mesh behind it may deliver a third of the free area its size suggests. Measure the open area itself, ignoring the overall size of the frame. The two figures can differ by a factor of three.

That distinction catches owners and a fair number of contractors as well. Fitting six handsome cast vents with tight mesh can deliver less airflow than three plain openings of the same nominal size, and a vent painted over several times has less again. Where a house appears to have adequate vents and still smells damp, measuring the actual free area is the check that explains it, and it frequently explains it completely. A houseful of handsome vents with almost no free area behind them is a surprisingly common finding, and it explains why the house still smells. Free area is the figure that counts rather than the vent count.

Cross-flow is the rule that matters more than the arithmetic, and it is the one most often broken. Air only moves through a subfloor if it has somewhere to enter and somewhere to leave on a different side, which means vents spread across opposite or adjacent walls, which rules out a single face. A house with ten vents across the front wall and none at the back has ten decorative holes, because there is no pressure difference to drive anything through them. Air needs somewhere to leave as much as somewhere to enter, which is the whole of the cross-flow idea. Everything else worth knowing about subfloor ventilation follows from that one idea.

Internal obstructions defeat cross-flow just as thoroughly as missing vents. Masonry dwarf walls, perimeter beams, brick piers built up into continuous walls, concrete tank bases, ducting, stored material and an added slab for a built-in room all divide a subfloor into compartments. Each compartment needs its own path in and out, which is why a house that ventilates well along two sides can have a stagnant dead zone in the middle that smells and rots. Those zones are where decay is almost always found first, and they are also where nobody thinks to look. Ask the inspector to photograph the middle of the subfloor specifically.

Corners deserve specific attention because they are where air stagnates. Ventilation openings positioned close to each corner of the building, instead of evenly spaced along the middle of each wall, do far more for the areas that would otherwise never see moving air. On a rectangular house, vents near the corners plus one or two mid-wall openings outperform the same number spread evenly along the walls. Where the openings sit matters at least as much as how many of them there are. Four well-placed openings beat eight badly placed ones.

Clearance to the ground is the companion requirement, commonly compromised over time. Minimum clearances exist between the ground and the underside of bearers and flooring, both so air can move and so there is room to inspect, and they get eaten away by garden beds, mulch, fill, new paving and material stored underneath. A subfloor with 150 millimetres of clearance cannot be ventilated properly whatever is cut into the walls. Clearance is the precondition everything else here depends on. Without it, cutting vents is money spent on appearances.

Fans have a genuine place and a narrow one. Where a subfloor is compartmented, where the site has no prevailing breeze, or where an addition has sealed one side permanently, mechanical extraction at $650 to $1,600 for a single unit or $1,800 to $4,500 for a humidistat-controlled system does work that passive openings cannot. The configuration matters, since the right arrangement extracts stale air and lets replacement air in through passive vents, and a fan blowing into a sealed space achieves very little. Units from Fantech, Edmonds and Solar Whiz are the ones most regularly fitted under Queensland houses, and the control arrangement matters more than the brand. Our underfloor ventilation installation page covers the systems in more detail.

The owner's audit is therefore four measurements and a walk. Measure the total length of external wall enclosing the subfloor, add up the genuine free area of every unobstructed vent, check whether vents exist on at least two different sides, and measure the clearance from ground to bearer at several points. Those four numbers tell you whether you have a ventilation problem before anybody quotes to fix one. Write the four numbers down and keep them. Every contractor who attends will be asking the same questions.

Dealing With Moisture Where It Starts

Ventilation removes moisture that is already in the air. Attacking the source removes it before it gets there, and on most Queensland houses the source work is both cheaper and more effective. Owners who start with a fan and finish with a vapour barrier usually discover they did not need the fan at all. Working in the other order wastes both the money and the time. Deal with the source first, then with air movement, and only then with equipment.

Bare soil is the largest single source, and relentless with it. Ground under a house evaporates moisture continuously, and the rate depends on how wet the soil is, with the weather on the day barely relevant, which is why a subfloor over damp clay stays humid through a dry week. Laying a continuous sheet of polythene across the ground, lapped at the joins and turned up slightly at the perimeter, cuts that evaporation dramatically for $18 to $40 the square metre. No other item on the rate table returns as much for the outlay. It is also the item most routinely absent from a ventilation quote.

The vapour barrier is the highest-value single intervention available under most houses and it remains strangely unpopular. It needs weighting down with sand, pavers or gravel and never left loose, it needs to run right to the perimeter without stopping short, and it should not trap water above it, which means it suits a subfloor that stays dry in rain, which excludes one that floods. Where water actually flows through the space, drainage has to come first.

External water is the second source and the cheapest to fix. A gutter spilling over at a joint, a downpipe emptying against the base of a wall, stormwater tracking along a path towards the building, a dripping tap beside a vent, and an air conditioning condensate line running out under the floor all deliver water where it does the most damage. Walking the perimeter during heavy rain for five minutes identifies most of this, and stormwater drainage work fixes it. Take a photograph while the water is running, since the evidence disappears the moment the rain stops. A photograph of water running under the house settles any argument about the cause.

Ground falls matter as much as the pipes. Soil, paving and garden beds that fall towards the building send surface water under the house every time it rains, and regrading at $45 to $120 the metre reverses it. The target is a fall away from the wall over the first metre or so, and where a path or slab has been laid flat or back-falling, cutting and relaying the edge is the honest fix rather than adding drainage to carry water that should not have arrived. Stopping it at the source is almost always the cheaper option. Carrying water away is what you resort to when you cannot stop it arriving.

Subfloor drainage handles what cannot be kept out. A spoon drain or an agricultural line laid in the lowest part of the subfloor and taken to daylight at $120 to $320 the metre intercepts water crossing the site, and on a sloping block where the house sits in the path of overland flow it may be the only answer. Where there is no fall to daylight, a sump and pump at $1,500 to $4,500 does the job, and subsoil drainage contractors handle both arrangements. A pump needs power and maintenance, so gravity drainage is preferable wherever the fall exists. A pump that fails in a storm fails at exactly the wrong moment.

Plumbing leaks are a source people overlook because they assume they would know. A weeping joint on a supply line, a cracked sewer connection, a failed shower waste or a slow drip from a laundry tub beneath a highset house can put litres a day into the soil without any visible symptom upstairs. A subfloor that is wet in one localised area, particularly under a wet room, is a plumbing question before it is a ventilation question. One wet corner under a bathroom has a single cause and a plumber will find it faster than a builder.

Stored material is a source in its own right and clearing it is free or nearly so. Timber offcuts, cardboard, old carpet, bagged soil, firewood and garden waste all hold moisture, release it slowly, block airflow and feed termites. Clearing a subfloor at $400 to $1,500 depending on quantity and access frequently produces a measurable drop in humidity on its own, and skip bin hire is the main cost where there is a lot of it. The labour is in carrying it out in place of in removing it from the site. Access therefore matters more than quantity on this line.

Measuring is what proves any of this worked. A moisture meter reading on the same joists before and after, taken in the same season, is the only honest evidence that an intervention achieved something. A contractor who takes baseline readings, does the work and returns to measure again is offering a result, which a product alone is not, and on a subfloor that distinction is worth paying for. Ask for the baseline reading in writing before any work is scheduled. Without a baseline there is nothing to compare against afterwards.

Rot, Borers and Termites: Telling Them Apart

Three quite different things damage subfloor timber and they call for three different responses, so misidentifying one as another wastes money in both directions. An owner with a torch and a screwdriver can usually sort them out, and knowing which you have determines whether you need a builder, a pest manager or nothing at all.

Moisture content is the governing number for decay. The fungi that rot structural timber need the wood carrying somewhere around twenty percent moisture before they can establish, and at about fifteen percent or less they cannot start at all. That threshold is why every moisture intervention in this guide matters, and it is also why drying a subfloor out halts active decay without any treatment at all. A meter reading is therefore more useful than any opinion. Ask for the number and the location it was taken at.

Brown rot is the version that worries structural engineers. It breaks down the cellulose and leaves the timber dark, shrunken and cracked into a cubical pattern, light in the hand and crumbling to powder under a screwdriver. It travels along a member and can extend well past the visibly affected area, which is why a probe test every few hundred millimetres along a bearer tells you more than looking does. Timber in that condition has lost capacity and needs replacing and not treating. No product restores strength to timber that has already gone.

White rot and soft rot behave differently and are generally less aggressive. White rot leaves the timber pale, fibrous and stringy, not cubical, and soft rot produces a soft surface layer over sound timber beneath, which is common on the underside of flooring over a damp subfloor. A soft surface on an otherwise solid joist is often treatable once the moisture is dealt with, and structural inspection work establishes how deep it goes. A probe every few hundred millimetres along the member is how that gets measured, since the surface tells you very little about the depth.

Borers are the most commonly misdiagnosed and regularly need no action whatsoever. Lyctid borers attack the sapwood of hardwoods, which matters in Queensland because so much subfloor framing is hardwood, and they produce fine powder and small round exit holes confined to the sapwood band. The damage is cosmetic and self-limiting, since the beetle cannot reuse the same timber and the heartwood is immune. Replacing a sound hardwood bearer because of lyctid holes is a genuine waste of money. Ask which species of borer has been identified before agreeing to any treatment.

Anobium borers in softwood flooring are a different matter and worth distinguishing. They attack seasoned softwood, including pine flooring and plywood, and they do re-infest, so an active population can progressively weaken a floor over years. Fresh powder that reappears after being cleaned away indicates activity; old grey-filled holes with no new dust indicate a historical problem. Treatment through pest control contractors is worthwhile where the activity is current. Clean the powder away and check again in a fortnight.

Termites are the serious one and the identification is usually straightforward once you know the signs. Subterranean termites leave mud leads and galleries, fill their workings with soil and faecal material, hollow timber from the inside leaving a thin shell, and prefer the softer spring growth, producing a layered honeycomb when broken open. Any mud lead on a stump, a pier, a bearer or an ant cap is active evidence and the correct response is to stop rather than touch it, and call a licensed pest manager. Disturbing a lead scatters the colony and makes the inspection considerably harder, which is the opposite of helpful.

Ant caps are part of the system and they are almost always compromised. The metal shields on top of stumps and piers exist to force termites out into view where an inspector will see them, which only works if they are intact, unbridged and visible. Soil heaped against a stump, paving laid over the shield, stored timber leaning on a pier and a built-up garden bed all defeat them, and reinstating them at $45 to $120 each is cheap once the obstructions are cleared. Physical barrier products such as Termimesh and chemical systems including Kordon appear under a great many Queensland houses, and the durable notice in the meter box records what was installed. The management requirements sit in AS 3660.1 and termite damage repair follows any structural finding.

Asbestos belongs here because it is so common in Queensland subfloors. Sheeting used to enclose under-house areas, old pipe lagging, and fragments of broken sheet in the soil are all realistic finds in houses built before the late 1980s, well before the James Hardie product range moved to cellulose fibre cement, and disturbing bonded material releases fibres. Nobody should be cutting, drilling or breaking sheeting under a house without establishing what it is, and the Queensland asbestos information service sets out how bonded material is identified and handled.

Stumps, Bearers, Joists and Floors

Structural repair under a house follows a logic that runs from the ground upward, and getting the order wrong is how owners pay twice. The ground supports the stumps, the stumps carry the bearers, the bearers carry the joists, and the joists carry the floor and everything standing on it. A problem at any level shows up as movement at the top, so working from the top down fixes symptoms and leaves causes in place. The order of investigation runs from the ground upward, every time. Working the other way treats the symptom and leaves the cause.

Stumps and piers come first because everything else sits on them. Timber stumps rot at ground level where moisture and oxygen meet, which means a stump can look sound above ground and be gone at the base, and the test is to probe it at and just below ground level rather than at eye height. Concrete stumps crack and spall, usually where reinforcement sits too close to the surface, and steel stumps corrode at the ground interface for the same reason timber rots there. Probe or tap every stump at and just below ground level instead of at eye height, because that is where the two conditions decay needs actually meet. A stump that rings solid at waist height can be gone at the base.

Replacing stumps individually suits localised failure and costs $350 to $900 each. The work involves supporting the bearer above, removing the old stump, excavating and forming a new footing sized for the ground conditions, and setting the new stump to the correct height with an ant cap on top. Where more than roughly a quarter of the stumps are at end of life, restumping contractors will generally recommend doing the lot at $12,000 to $35,000, because a partial job leaves a system of mismatched age and stiffness. A house supported half on new stumps and half on forty year old ones moves unevenly for the rest of its life, which shows up upstairs as cracks that keep coming back. That is the argument for doing the lot at once.

Bearers are next and they fail in two ways. Decay at the bearing points over stumps is the common one, since that is where water sits and air does not move, and it is also where the load concentrates. Deflection is the other, where a bearer spanning too far between stumps sags over decades, which produces a dished floor in place of a dropped one. Replacement runs $180 to $450 the metre, and adding an intermediate stump is sometimes the better answer to a span problem. It costs a fraction of replacing the member.

Joists fail more locally and the repair options are wider. A joist with section loss at one point, from a plumbing penetration cut badly, a wet patch under a shower or borer damage, can routinely be sistered, which means fixing a new member alongside the damaged one for $120 to $300. Full replacement at $220 to $550 each suits a joist that has decayed along its length. Notching and drilling limits matter here, because a joist with a 60 millimetre notch cut for a waste pipe has lost far more capacity than the notch suggests.

Flooring is the top layer and the most visible. Cupped boards indicate moisture from below and will frequently flatten right out once the subfloor dries, so replacing them before the subfloor is sorted is premature. Boards that are soft, split, or have lost thickness need replacing at $90 to $220 the square metre, and matching old hardwood flooring is its own challenge, with reclaimed boards usually reading better than new ones. The options are set out on our timber flooring page.

Levelling a floor is where expectations need managing. A floor that has settled can be propped and jacked back towards level at $800 to $2,500 for a section, and the process has consequences upstairs, since lifting a floor moves the wall frames standing on it and will open some cracks while closing others. Internal patching and painting therefore belongs after the structural work and never before, and attempting to do it first means doing it twice. Lifting a floor opens some cracks upstairs and closes others, so the internal work only makes sense once the structure has settled into its new position.

Load paths deserve a thought before any alteration. Walls added under a house during a build-in, a bathroom relocated upstairs, a heavy stone benchtop in a renovated kitchen, or a water tank placed on a deck all add load that the original stump layout was not sized for. Where the floor has started to sag under something added later, the answer is additional support, leaving in place what is already there, and a structural engineer sizes it. Adding an intermediate stump under a sagging bearer is cheap, while replacing the bearer is not, so the assessment is worth having before committing.

Access and confined space rules govern how this work is done and who can do it. A subfloor with limited clearance and a single entry point can meet the definition of a confined space, which brings specific requirements for atmosphere, entry procedure and a person outside, and WorkSafe Queensland publishes what applies. A contractor who raises access and ventilation of the work area before quoting is telling you they have done this properly before, and structural repair specialists work to those requirements routinely.

Built-In Subfloors and Recovering From Flood

Two Queensland situations deserve their own treatment because they break the normal rules. The first is the enclosed under-house area, which is close to universal on highset homes in this state and which almost always traded ventilation for floor space. The second is inundation, which a great many subfloors across the Brisbane, Ipswich, Lockyer and Fitzroy catchments have experienced and which leaves a specific set of problems behind. Both situations break the normal sequence of works and deserve their own treatment, which is why they sit together here.

Building in under a highset house is an attractive proposition and a common one. A rumpus, a laundry, a garage, a bathroom or a whole second dwelling appears where there was only air, usually for a fraction of the cost of adding upstairs. The structural side of a build-in is normally done perfectly well. What changes invisibly is that the ventilated open space beneath the house becomes an enclosed room, and the part that remains unenclosed loses the cross-flow it previously relied on.

The result is a subfloor divided into zones with different problems. The enclosed room has habitable-room requirements of its own and generally performs acceptably. The remaining crawl space behind or beside it, often reduced to a strip, commonly has vents on one side only, no path for air to leave, and a slab edge or masonry wall sealing it off from what used to be an open underside. That strip is where the smell, the mould and the decay concentrate.

Retrofitting ventilation into that geometry needs thinking more than counting. Vents cut into the new enclosing wall, a path through or around the added slab, and in many cases mechanical extraction are what restore movement, because there is no longer a natural pressure difference across the space. This is the single most common situation in which a fan truly earns its cost in Queensland, and it is worth saying so plainly. Everywhere else in this guide a fan quoted before the passive work has been assessed deserves a question, so the exception matters.

Anyone planning a build-in should deal with this while the job is still being designed. Keeping a ventilation path through or around the new work, providing vents in the new walls, laying a vapour barrier over any remaining soil before the work closes it off, and leaving an access hatch into the retained crawl space are all cheap during construction and expensive later. Where the build-in is already done and the problem exists, the fix is retrofitted openings and extraction. Neither is expensive once somebody has worked out where the air can actually go, and that thinking is the valuable part of the job.

Inundation is the other situation and the first rule is that an enclosed subfloor traps water. An open highset underside drains and dries within days. A built-in area, a subfloor with perimeter masonry, or one with a vapour barrier holding water above it can stay wet for months, and timber that stays above twenty percent moisture for months is timber that will rot. Getting water out quickly matters more than anything else in the first week.

Silt is the second problem, and routinely underestimated. Flood deposits hold moisture against timber, carry contaminants, and fill the ventilation openings and the gaps around ant caps. Removing it at $45 to $120 the square metre is unglamorous and necessary, and it has to happen before drying can work. Insulation batts that have been wet are a total loss and need removing at $25 to $60 the square metre instead of being left to dry in place, and that applies to glasswool products from Bradford or Knauf Earthwool as much as to anything else.

Drying properly takes longer than people expect and measuring is the only way to know. Structural hardwood that has been submerged can take months to return below the decay threshold even with good airflow, and a floor that feels dry on top may still be carrying high readings in the joists. This is where flood damage restoration contractors with meters and air movers earn their fee, and where closing the floor back up too early causes the real damage. The right approach is to measure the timber in place of guessing at it.

Assessment afterwards should be structural as well as cosmetic. Flowing water scours soil from around footings, moves stumps, washes out bedding under piers and can leave a stump standing in a void. Where water moved through at any depth, the stumps and footings need looking at as well as the timber above them, and in a declared event storm damage repairs may be covered by insurance in a way that gradual decay is not. Photograph the whole subfloor before anybody starts clearing silt or timber, because that record is what supports the claim. Where a claim is declined and you disagree with the reasoning, the Australian Financial Complaints Authority handles insurance disputes at no cost to the complainant.

Subfloor Costs by Queensland Region

Rates move with labour availability and travel, and the dominant subfloor problem changes markedly with climate and housing type. The figures below cover an inspection with photographs and a ventilation improvement package of four vents plus a vapour barrier under a typical footprint, with the condition that drives most local work and a note on what to deal with first.

Two patterns run through those figures and both are worth noting. Labour rates climb steadily with distance from the south east, and the spread widens because a contractor covering a large district prices travel into every attendance and cannot absorb a return visit to take follow-up moisture readings. Materials barely move, since polythene sheeting, vents and timber are cheap to freight relative to the hours involved, though a fan or a humidistat controller can take a week to arrive in the far north.

Climate decides which intervention actually earns its keep. Through the south east and the Downs, correcting water and cross-flow resolves most cases and a fan is usually unnecessary. From Mackay north and especially around Cairns and the Tablelands, humidity stays high enough for long enough that mechanical extraction is really justified more often, and drying times after any wetting event stretch considerably. Inland and west, the problem inverts and becomes termite pressure in dry soil, not fungal decay.

Housing type decides where the work happens and how hard it is. Highset timber homes through Brisbane, Wide Bay, Rockhampton and the far north put everything in an accessible crawl space, which is both the problem and the opportunity. Lowset timber-floored houses on short stumps give 300 to 400 millimetres of clearance where every hour of labour costs more. Brick-based houses with perimeter walls and small vents are the hardest to ventilate and the most likely to need openings cut and a fan fitted.

Clearance is the quiet multiplier everywhere on that list. At 900 millimetres a tradesperson works at normal speed. At 500 they work on their knees at half speed. At 350 the job becomes a crawl with material dragged in piece by piece, and excavating to gain height at $90 to $220 the square metre sometimes costs less than working in what is there. Where excavation is considered, excavation contractors need to understand that footings must not be undermined.

What to Look Out For in a Subfloor Quote

Subfloor work attracts a wide spread of operators, from building inspectors and pest managers through to ventilation companies, handymen and restumping specialists, and the quotes they produce routinely address completely different problems. The spread between a correct fifteen hundred dollar solution and an unnecessary twelve thousand dollar one is real, and a handful of questions separates them.

Start by requiring an inspection with photographs before any quote. Nobody can price subfloor work honestly without having been under the house, and an owner who has not seen photographs is accepting a description of a space they cannot verify. An inspection at $280 to $650 producing dated images of the stumps, bearers, joists, ground surface and ant caps is the document every subsequent quote should reference. Without it you are comparing descriptions of a space nobody has shown you, which is not a comparison at all.

Ask for moisture readings and a number, never an adjective. Damp is an opinion; a reading of twenty-two percent on a particular bearer is a fact, and it establishes whether decay is possible. A contractor who arrives with a meter and records readings at identified locations is giving you a baseline you can measure the work against afterwards, which is the only way to know whether anything improved. Diarise a follow-up reading for the same season next year, since a reading taken in a different season proves nothing either way.

Be sceptical of a fan proposed before the passive ventilation has been assessed. Mechanical extraction has a real place and is not the first move on most houses, so a quote that leads with a multi-fan system before anybody has counted the free area of the existing vents, checked for cross-flow or looked at the ground has sold a product without diagnosing a problem. Ask what the audit of the existing vents actually showed. If no audit of the existing openings was done, the fan is a guess with a price attached.

Insist that the vapour barrier and the water sources are addressed in the scope. Bare soil and misdirected stormwater are the two biggest moisture inputs under most Queensland houses, and both are cheap to deal with. A ventilation quote that omits a vapour barrier and says nothing about where the downpipes discharge is proposing to extract moisture indefinitely as opposed to stopping it being produced. Extraction running over bare soil is a permanent operating cost with no end point, which is a poor trade against a single sheet of plastic.

Separate the structural quote from the moisture quote. Timber measured in a wet subfloor reads worse than the same timber after a season of drying, and cupped flooring frequently flattens out once the moisture source is gone. Having the moisture work done first and the structural assessment repeated afterwards often reduces the structural scope, and a contractor willing to stage it that way is working in your interest. The staged approach usually costs less in total as well, which is the part owners find hardest to believe.

Check the licence against the value and the class of work. Building work in this state above $3,300 including materials requires a contractor licensed for that class, together with a contract in the prescribed written form, plus a home warranty notice once the value crosses the threshold. The licence number can be searched on the Queensland Building and Construction Commission register in under a minute. Termite work is a separate licensing regime again, so one contractor may need two credentials or you may need two contractors. Establish which arrangement applies before the work is scheduled.

Ask who is responsible for pest findings and what happens if termites are discovered mid-job. Opening up a subfloor commonly reveals activity nobody knew about, and the sequence matters, since treating the colony comes before repairing the timber it damaged. Agreeing in advance how such a finding will be handled and priced prevents a stalled job and an argument, and the Queensland Government portal explains how the licensing frameworks fit together. Confirm the sequence in writing before a deposit is paid, because a stalled job halfway through a subfloor is an expensive place to be.

Know the complaint pathway before you need to use it. A defect complaint about a licensed contractor is lodged with the QBCC, which applies separate time limits to structural and non-structural matters. Where that process does not settle it, the Queensland Civil and Administrative Tribunal hears it next. Running alongside both, the consumer guarantees set out by the Australian Competition and Consumer Commission cover the workmanship and the products supplied, fans and barriers included. Photographs taken under the house during the work are the evidence that makes any of that usable. Ask for them as the job proceeds, since afterwards is too late, since nobody can photograph what has already been replaced.

Finally, ask about access, confined space and asbestos before work starts. A low subfloor with one entry can meet the definition of a confined space with its own entry requirements, and sheeting or debris under a pre-1990 house may contain bonded asbestos that must be identified before anything is cut or broken. A contractor who raises both unprompted has worked under Queensland houses before, and one who dismisses them has not. Neither point is negotiable on a pre-1990 house with low clearance.

Getting Subfloor Quotes Across Queensland

Two or three quotes is right once an inspection report exists, and close to useless before one. This is the repair where owner preparation makes the largest difference, partly because the space is hard to assess and partly because the cheap interventions are the effective ones and they only get quoted when somebody asks for them.

Do the perimeter walk and write it down before you call anybody. Count the ventilation openings on each wall separately, note which are blocked, painted over, buried or screened with fine mesh, measure the clearance from ground to the underside of the bearer at several points, and note where the ground falls towards the house. Four numbers and a sketch is enough to start a sensible conversation. It also tells you roughly whether to expect a four figure quote or a five figure one, which is useful before the first conversation.

Watch the house in heavy rain, since that is when the evidence appears. Look for a gutter overflowing at a joint, a downpipe discharging at the base of a wall, water sheeting across a path towards the building, and any point where runoff disappears under the floor. Five minutes in a downpour identifies more about a wet subfloor than an hour of inspection in dry weather. Take a short video while it is happening, because describing it afterwards never carries the same weight.

Get the inspection with photographs as a separate purchase, unbundled from any repair quote. An inspector with no repair work to sell has no reason to find more than is there, and the photographs become the common reference every contractor quotes against. Where a building inspection or a combined timber pest inspection is being arranged for another reason, add the subfloor to its scope. The marginal cost of adding the subfloor to an inspection already booked is small.

Ask for baseline moisture readings and keep them. Note the date, the season and the location of each reading, because the comparison in twelve months is what proves whether the work achieved anything. On a subfloor, that single page of numbers is worth more than any warranty document, and nobody will create it for you unless you ask. A single dated page with each reading location named is all it takes.

Deal with the items that cost nothing yourself first. Clearing stored material, pulling mulch and soil back off the vents, cutting a shrub away from a wall, unblocking a downpipe outlet and scraping paint out of a painted-over vent cost nothing and sometimes produce a measurable change. Doing them before the inspection also means the report describes the house as it will be and not as it was. There is no value in paying somebody to document a pile of old timber.

Bundle the work that becomes cheap while somebody is already under there. A vapour barrier laid during a stump replacement, drainage dug while the space is cleared, new underfloor insulation fitted once the timber is dry, or a drainage line installed while the subfloor is open all cost a fraction of a separate mobilisation. An access hatch cut at the same time makes every future visit cheaper and every future inspection more thorough.

Keep the documentation and the photographs somewhere you will find them. The inspection report with its images, the baseline and follow-up moisture readings, the written contract with the licence number, the specification naming the barrier material and any fan model and its control arrangement, pest treatment certificates and any updated termite management notice, and the home warranty notice where the value required it. On a subfloor the photographs are irreplaceable, because nobody can go back and look at what was there before the work. Post your job on The Quote Yard to receive quotes from licensed builders, restumping specialists and ventilation installers across Queensland.