Slab on Ground or Raised on Stumps?
Once you've decided to build a shed in South East Queensland, the next big call is what sits underneath it. The two main contenders are a concrete slab poured directly on the ground, or a raised sub-floor on stumps with bearers, joists and a timber or ply floor. Both work. Both are used across Brisbane, Logan, Ipswich and the wider SEQ region every day. The right answer depends on your block, your flood risk, what you're storing, and how long you want the thing to last.
This guide compares the two honestly: cost, durability, drainage, termite risk, flood resilience, anchoring, air flow, and how each handles a sloping block. By the end you'll know which option fits your site, without the sales pitch.
The Two Options Explained
Option 1: Concrete Slab on Ground
A concrete slab is a single monolithic pour, typically 100mm thick, reinforced with SL72 or SL82 mesh, sitting on a 75mm to 100mm compacted road base. The shed bolts directly down onto the slab and the slab is the floor. This is the standard build for the vast majority of garden sheds, workshops, and small garages in SEQ.
Option 2: Raised Shed on Stumps
A stumped sub-floor uses concrete, steel, or timber stumps founded in the ground at regular spacings (usually 1.8m to 2.4m apart). Bearers sit on top of the stumps, joists run across the bearers, and a timber or ply floor finishes the deck. The shed frame is then built on top of the floor. The space underneath is open, allowing air flow and water passage. This is the same basic system as a traditional Queenslander house, scaled down for a shed.
When a Concrete Slab Is the Right Choice
For most shed projects in Brisbane and SEQ, a slab is the simpler, cheaper, and longer-lasting option. It's the right call when:
- The block is flat or near flat, so cut and fill costs stay low
- The property is not in a flood overlay
- You'll park or store vehicles, ride-on mowers, or trailers in the shed
- The shed is a workshop with heavy benches, lathes, or compressors
- You want strong tie-down for cyclone or high-wind anchoring
- You want a base that you can forget about for the next 40 to 50 years
If those describe your situation, you're in the majority of SEQ shed owners, and a slab is the obvious answer. See our shed slabs service page for full specifications.
When Stumps Make More Sense
There are real situations where a raised, stumped sub-floor is the smarter pick. Stumps win when:
- The block is very steep and cut and fill or a stepped slab would be expensive and disruptive
- The property sits in a flood overlay (Brisbane River, Bremer River, Logan River, Albert River, creek flats) and you need to raise the shed floor above the defined flood level
- You want air flow underneath to keep timber stored items dry in a humid spot
- You're matching a heritage Queenslander style on the same block and want visual continuity
- You want the shed to be reversible with no permanent footprint on the lawn
Cost Comparison
For a typical 3m x 3m garden shed footprint, here's how the two options stack up on cost.
| Base Type | 3m x 3m Shed | 6m x 6m Shed | Notes |
|---|---|---|---|
| Concrete slab on ground | From $1,500 | From $4,500 | Installed, mesh reinforced, broom finish |
| Stumps + bearers + joists + ply floor | From $2,000 (materials) plus labour | From $5,500 (materials) plus labour | Steel stumps; timber floor system |
| Stumps on a steep block | Often cheaper than cut and fill slab | Often cheaper than stepped slab | Savings grow as slope increases |
All prices are indicative starting-from guides only. Final pricing depends on site conditions, access, soil type, and specific requirements.
On flat ground the slab usually wins on cost. On a 1-in-4 sloping block, stumps frequently come out cheaper once cut and fill or stepped slab formwork is factored in. For a full breakdown of slab pricing, see our pricing guide or use the shed slab calculator.
Durability and Lifespan
Concrete Slab: 50+ Years
A properly built shed slab on a well prepared base will sit there quietly for 50 years or more. Concrete doesn't rot, doesn't get eaten by termites, doesn't sag under load, and doesn't need anything more than a sweep every now and then. Reseal an enclosed workshop floor once a decade and you're done.
Timber Stumps: 20 to 30 Years
Timber stumps, even treated hardwood, typically last 20 to 30 years in SEQ before rot at the ground line or termite damage becomes a problem. Replacing rotten stumps under an existing shed is doable but messy: jack the bearers, dig out the old stump, pour a new one, lower the load back down.
Steel or Concrete Stumps: 50+ Years
Galvanised steel stumps or precast concrete stumps last as long as a slab. If you're going stumped, paying the extra for steel or concrete stumps over timber pays for itself many times over in avoided replacement work.
Drainage
Slab: Plan the Fall
A concrete slab is waterproof, so any rain that hits the slab needs somewhere to go. Your concreter will pour a small fall (usually 1:100) away from the shed door, and that handles most situations. In a low spot, you may need a strip drain or an agricultural drain on the uphill side to stop water washing against the slab edge.
Stumps: Water Passes Underneath
With stumps, water just runs across the natural ground beneath the shed. No fall to design, no drainage channel needed, no risk of pooling against a slab edge. This is genuinely useful on creek flats, low spots, or sites where stormwater flows across the yard during heavy rain.
Termite Risk
Slab: Very Low
A concrete slab has no timber in direct contact with the soil, so termites have nothing to chew. The shed frame itself is usually steel (Colorbond kit sheds), which means the whole structure is termite-proof from the ground up. This is a real advantage in Brisbane and SEQ, where termite pressure is high year-round.
Stumps: Depends on Material
Timber stumps in ground contact are a termite buffet unless they're treated to H5 and properly capped, and even then they're a higher risk than concrete. The bearers, joists and floor above are all timber too, sitting directly above the stumps. If termites get into the stumps they can travel up into the floor system.
Steel or concrete stumps eliminate the ground contact risk. Pair them with a steel frame shed and you're effectively termite-proof. If you're going stumped in SEQ, this is the sensible specification.
Flood Resilience
This is where stumps genuinely shine, and where slabs struggle.
Slab in a Flood
A concrete slab handles being submerged just fine, structurally. The problem is everything inside: tools, machinery, stored boxes, gardening gear. The contents of the shed get wet whenever water rises above the slab level. After the 2011 and 2022 Brisbane floods, plenty of slab-based sheds in low-lying suburbs lost everything inside.
Stumps in a Flood
A raised shed on stumps lets flood water pass underneath. If the floor level is set above the defined flood level for the property, the contents stay dry while the flood passes. For properties in mapped flood overlays along the Brisbane River, Bremer River, Logan River, Albert River, or any of the SEQ creek flats, stumps are the standard answer.
Anchoring the Shed Down
Slab: Simple and Strong
Anchoring a kit shed to a concrete slab is straightforward. Most manufacturers specify M10 or M12 dynabolts (mechanical anchors) drilled into the cured concrete, or cast-in anchor bolts placed during the pour. Either way, the connection is direct steel-to-concrete, and the wind-rating certification from the manufacturer is built around this setup. See our guide on how to anchor a shed to a concrete slab for full detail.
Stumps: More Engineering Required
With a stumped sub-floor you need to tie down through three layers: the shed frame to the floor, the floor to the bearers, and the bearers to the stumps. Each connection needs to be designed for the wind load. On taller stumps in higher wind zones, this gets into proper engineering territory with cyclone rods running from the bearer all the way down to the stump footing.
It's all doable, but it's more complex, more expensive, and more important to get right. We can pour stump footings to engineering specifications when needed.
Air Flow and Damp
Slab: Vapour Barrier Matters
Moisture can rise up through a concrete slab from the soil below (called rising damp). A plastic vapour barrier under the slab during pouring blocks this, and it's standard for any enclosed workshop. Without a vapour barrier, you'll see condensation forming on the slab on cool mornings, and stored cardboard or timber can wick moisture.
Inside a steel-clad shed, condensation on the underside of the roof during cold nights is a separate issue, and is solved with anti-condensation blanket or insulation, not the slab itself.
Stumps: Natural Ventilation
Air flow under the floor keeps the timber dry and stops damp building up. For storing tools, books, fabric, or anything moisture-sensitive, a well-ventilated stumped sub-floor performs better than a slab without a vapour barrier. The trade-off is that the floor itself can feel cooler in winter and warmer in summer because there's no thermal mass underneath.
Sloping Blocks: Where Stumps Win on Cost
On a flat or gently sloping block, a slab is cheap to build. As the slope steepens, slab costs climb fast:
- Cut and fill means excavating the high side and compacting fill on the low side. The fill must be engineered compacted to take a slab load, or the slab will crack as it settles
- Stepped slab means pouring the slab in two or three levels with retaining at each step, doubling or tripling the formwork cost
- Retaining walls on the downhill edge add another major cost line
Stumps handle slopes far more elegantly. The stumps are simply cut to different heights so the bearers above sit level. On a 1-in-4 or steeper block, stumps often come in 30% to 50% cheaper than the equivalent slab once retaining is factored in.
The break-even point is around a 1-in-10 slope across the shed footprint. Flatter than that, slab wins. Steeper, stumps start to win.
Brisbane and SEQ-Specific Factors
Reactive Clay Soils
Much of Brisbane, Logan and Ipswich sits on reactive clay (Class M or H sites). Clay swells when wet and shrinks when dry, which puts cyclic stress on whatever's built on it. For a slab, this means a properly designed thickened edge beam or stiffening ribs depending on the site classification, and a good compacted base. For stumps, it means deeper footings (often 600mm to 1,000mm) into stable ground below the reactive zone.
Both options handle reactive clay when designed correctly. Both fail when shortcut. See our guide on do I need footings for a shed slab for more on slab design on reactive ground.
Flood Overlays
If your block sits within a council flood overlay (check Brisbane City Council, Logan City Council, Ipswich City Council, Moreton Bay Regional Council, Gold Coast City Council or Redland City Council flood mapping), stumps are usually the preferred option for any shed you'll use to store items of value. The defined flood level dictates the minimum floor height.
Cyclone Wind Zone
SEQ sits in wind regions A2 to C, depending on location and exposure. Both slabs and stumps can be detailed to handle the wind load. The difference is in anchoring complexity (see above). A slab makes high-wind anchoring simpler; stumps make it more involved but still very achievable with the right tie-down.
The Verdict for Most SEQ Shed Owners
For the majority of shed builds in Brisbane and South East Queensland, a concrete slab on ground wins. It's cheaper for small to mid-size sheds on flat or gently sloping blocks, lasts longer than timber stumps, makes anchoring straightforward, keeps termite risk down, and needs almost no maintenance over its life.
Stumps win when the block is steep enough that cut and fill becomes expensive, when the property is in a flood overlay, when you want air flow underneath for moisture-sensitive storage, or when you're matching the look of an existing raised Queenslander on the same block.
If you're not sure which fits your site, the easiest test is to walk the block: is it flat or close to flat, and does it stay dry in heavy rain? If yes, pour a slab. If the answer to either is no, get a quote on both and compare.
Concrete Slab vs Stumps: At a Glance
| Factor | Concrete Slab | Stumped Sub-Floor |
|---|---|---|
| Upfront cost (flat block) | From $1,500 (3x3m) | From $2,000 materials plus labour |
| Upfront cost (steep block) | Expensive (cut and fill) | Often cheaper |
| Lifespan | 50+ years | 20 to 30 (timber); 50+ (steel or concrete stumps) |
| Termite risk | Very low | High (timber stumps); low (steel or concrete) |
| Flood resilience | Contents get wet | Contents stay dry above flood level |
| Drainage | Needs fall away | Water passes underneath |
| Air flow / damp | Needs vapour barrier | Natural ventilation |
| Anchoring | Simple (dynabolts) | Complex (multi-layer tie-down) |
| Vehicle storage | Yes, drive in and out | No (raised floor) |
| Maintenance | Minimal | Stump checks, occasional replacement |
Frequently Asked Questions
For most small to mid-size sheds on flat or near-flat ground, a concrete slab works out cheaper than stumps. A 3m x 3m slab starts from around $1,500 installed. Stumps typically run $2,000 or more in materials alone before labour, plus a timber bearer and floor system on top. Stumps only become competitive when the block is so steep that a slab would need major cut and fill or stepped formwork.
If your block sits within a Brisbane City Council, Logan, Ipswich or Moreton Bay flood overlay, raising the shed on stumps above the defined flood level is the standard approach so stored items stay dry when water passes underneath. A concrete slab can still be built in a flood overlay, but the contents inside the shed will get wet during a flood event. Always check your council flood mapping and any specific overlay conditions before deciding.
Yes. Most kit shed brands including Fair Dinkum, Ranbuild, Stratco and Spanbilt can be installed on a stumped sub-floor with bearers, joists and a timber or ply floor. You will need to confirm the shed manufacturer accepts a stumped foundation in writing, since the structural warranty and wind certification often assume a slab. Anchoring also needs careful detailing so the frame ties down through the floor and into the stump tops.
On flat ground, shed stumps usually finish 300mm to 600mm above natural ground level to give air flow underneath and keep timber clear of soil. In flood overlay areas the height is dictated by the defined flood level for that property, which can mean 1.0m to 2.0m or more above ground. On sloping blocks the downhill stumps will be taller than the uphill stumps so the bearers sit level. Always confirm with your council and, for higher stumps, an engineer.
A properly built concrete slab will last 50 years or more with very little maintenance. Timber stumps typically last 20 to 30 years before rot and termite damage start to become a problem in SEQ conditions. Steel or concrete stumps last as long as a slab. For long-term, low-maintenance shed bases on flat ground, concrete is the easier call.
Related Reading
- Concrete slab vs paver base for a shed
- Do I need footings for a shed slab?
- How thick should a shed slab be?
- How to anchor a shed to a concrete slab
Important Disclaimer
This guide covers general information about shed base options in South East Queensland. Specific requirements for your project depend on site classification, soil type, flood overlay, wind region, shed manufacturer specifications, and council requirements. Always check your shed installation manual and consult an engineer where required (especially for higher stumps or sites in reactive ground).
We specialise in small concrete jobs only: shed slabs, garage slabs, concrete footpaths, water tank slabs and small pads. We can pour slabs and stump footings to engineering specifications when needed. All prices quoted are indicative starting-from guides only. Final pricing depends on site conditions, access, soil type, and specific requirements.
Get a Quote for Your Shed Base
If you've worked through the options and a concrete slab is the right call for your shed, we can give you a fixed quote based on your size, site and location. Stumped builds usually involve a builder for the floor system above, but we can pour the stump footings to engineering spec.
Next steps:
- Use the shed slab calculator for a quick cost estimate
- Browse the pricing guide for full slab pricing
- Read up on shed slab specifications
- Contact us for a free quote, tell us your shed size, your suburb, and whether your block is flat or sloping