Pouring a slab under a Queenslander.

Yes, and it is one of the most common jobs we do in the older Rockhampton suburbs. The catch is that a concrete truck cannot get under a house, so the concrete has to be pumped or barrowed into a space with limited headroom, working around existing stumps and posts that are holding the house up. It is slow, physical work rather than clever work. What decides whether it is straightforward or difficult is the clearance: over about 2.1 metres and it is comfortable, under about 1.8 metres and the labour cost climbs sharply.

This is a genuinely Rockhampton problem. The high-set timber house on stumps is the local vernacular for good reason: it lifted the floor above the flood line, it caught the breeze before air conditioning existed, and it kept the termites visible. What it also did was leave every home in North Rockhampton, Wandal, Allenstown and The Range with 60 to 120 square metres of dead space underneath. Concrete turns that into a workshop, a carport, a laundry or just somewhere you can put things down.

With a proper vapour barrier and drainage, and both matter more under a house than out in the open. Under the house the ground stays shaded and damp, air movement is poor, and any moisture that comes up through the slab has nowhere to go, so it shows up as damp, mould and that closed-up smell. We lay a 0.2mm polythene vapour barrier over a compacted crushed-rock base, tape the laps and turn it up at the edges, and we get the levels right so water falls away rather than sitting under the house. If the ground under there is already wet, it needs draining first.

The falls are the part that gets skimped. Out in the open a flat slab is a nuisance. Under a house a flat slab is a pond, because there is no sun to dry it and often no way for the water to leave. We fall these slabs out toward the perimeter at around 1 in 100 minimum and make sure the water has somewhere to go once it gets there. If the downpipes discharge under the house, and on old Rockhampton homes they often do, that gets fixed as part of the job or the slab is pointless.

The 0.2mm figure is not a rule of thumb either. AS 2870, the Australian Standard for residential slabs and footings that the National Construction Code Volume Two adopts as a deemed-to-satisfy solution, specifies a vapour barrier of polyethylene film not less than 0.2mm thick, branded as complying with the standard, with laps of at least 200mm taped and the membrane carried up at the edges. Sheeting sold as builders film is not automatically the same product, and the difference matters most in exactly this situation, where the ground never dries out. If someone quotes an under-house slab and the vapour barrier is not a named line item, ask what film and what lap.

There is a soil argument here too. Concentrating water under one side of the house is exactly what makes the black soil swell unevenly and move the stumps. So a properly drained under-house slab is not just a nicer floor, it is one of the better things you can do for the footings. The opposite case is covered in concrete cracks: when to worry.

Expect a premium over an open slab, because it is pumped or barrowed rather than chuted, and the headroom slows everything down. In 2026, budget roughly 130 to 190 dollars per square metre for a non-structural under-house slab with a vapour barrier and mesh, against 90 to 130 for the same slab poured in the open. Add a concrete pump at 650 to 1,500 dollars on most of these jobs, and add excavation if the ground has to be dug out to gain headroom. The tighter the clearance, the higher in the range you land.

A worked example from Wandal. A 1950s high-set with 2.3 metres of clearance and 72m² of open space underneath, no walls, no enclosure, just a floor. Grade and compact the base and lay the vapour barrier, 100mm slab with SL72 mesh, isolated around eleven stumps, falls to the north-east perimeter, two downpipes re-routed out from under the house. Slab at $150 per m² is $10,800, pump $950, downpipe work $400. All up about $12,150, no soil test, no engineering, no certifier, because nothing structural changed and nothing was enclosed.

Compare that to the enclosed version of the same space: soil test $650, engineered design $1,100, certifier $1,300, structural slab and footings instead of a floating floor, plus the walls. You are into a different order of money before a single stud goes up. Which is why our honest advice to most owners is to pour the floor, use the space open for a couple of years, and see whether you ever actually need the walls. Rates on the cost guide.

Can you pour a concrete slab under an existing Queenslander?

Yes, and it is one of the most common jobs we do in the older Rockhampton suburbs. The catch is that a concrete truck cannot get under a house, so the concrete has to be pumped or barrowed into a space with limited headroom, working around existing stumps and posts that are holding the house up. It is slow, physical work rather than clever work. What decides whether it is straightforward or difficult is the clearance: over about 2.1 metres and it is comfortable, under about 1.8 metres and the labour cost climbs sharply.

Does a slab under the house need to be structural?

Usually not, and this is the good news. The house is already carried by its stumps or posts on their own footings, so the new slab is not holding the building up. It is a non-structural floor slab, which means it does not need the deep engineered edge beams a house slab needs, and that keeps the cost down. It becomes structural the moment you ask it to do more: support a new blockwork wall, carry a bearer, or replace stumps as part of building in underneath. That is a different job with a different price.

Do I need approval to concrete under my Queenslander?

A plain slab on the ground under an open house, with nothing built on it and no walls going in, generally does not need building approval. The moment you enclose it, build a room in it, or add a wall or a bathroom, it becomes habitable or non-habitable building work under the National Construction Code and needs a private building certifier. In parts of Rockhampton you also have a flood overlay to consider, which can restrict what you are allowed to enclose and at what floor level. Check before you build, not after.

How do you stop damp coming up through an under-house slab?

With a proper vapour barrier and drainage, and both matter more under a house than out in the open. Under the house the ground stays shaded and damp, air movement is poor, and any moisture that comes up through the slab has nowhere to go, so it shows up as damp, mould and that closed-up smell. We lay a 0.2mm polythene vapour barrier over a compacted crushed-rock base, tape the laps and turn it up at the edges, and we get the levels right so water falls away rather than sitting under the house. If the ground under there is already wet, it needs draining first.

What does an under-house slab cost in Rockhampton?

Expect a premium over an open slab, because it is pumped or barrowed rather than chuted, and the headroom slows everything down. In 2026, budget roughly 130 to 190 dollars per square metre for a non-structural under-house slab with a vapour barrier and mesh, against 90 to 130 for the same slab poured in the open. Add a concrete pump at 650 to 1,500 dollars on most of these jobs, and add excavation if the ground has to be dug out to gain headroom. The tighter the clearance, the higher in the range you land.