A 6x9m Colorbond shed is one of the most popular larger sheds we pour for in Brisbane and SEQ. It's the size that fits a workshop, a car plus a trailer, or a serious storage shed with room left over. The footprint is 54 square metres, but here's the catch: the slab is not 6 by 9 metres. Pour it that size and you'll regret it within the first wet season.
This guide walks through the real slab dimensions you need, how thick to pour it depending on what's going inside, the mesh and edge spec, and the concrete volume to order. If you want to skip the maths, jump to our shed slab calculator.
The Short Answer
A 6x9m Colorbond shed needs a slab that's 100 to 150mm larger than the shed footprint on each side. So the minimum slab size is 6.2 x 9.2 metres, and 6.3 x 9.3m is even better if you have the room.
Thickness depends on what you're putting in the shed:
- Storage only: 100mm with SL72 mesh
- Storage with workbench and tools: 125mm with SL72 mesh
- Car, mower, trailer: 125mm with SL82 mesh
- Workshop with heavy machinery: 150mm with SL82 mesh
That's the headline. The rest of this article explains why each number is what it is.
Why You Don't Pour an Exact 6x9m Slab
If you've never built a shed before, it seems logical to pour the slab the same size as the shed. It isn't. Lining the wall sheets up with the slab edge causes three problems that show up fast:
- Water runs back under the shed: Without an overhang, rainwater hitting the wall sheets runs straight down the inside face and pools under the base rail. Within a year you get rust at the base of the sheets and damp inside the shed.
- No edge protection: The slab edge is the most fragile part of a slab. With no overhang, every knock from a mower, trailer or wheelbarrow chips the corner where the shed sits. Once the corner goes, water gets in and the steel near the edge starts to corrode.
- Harder to anchor: The shed manufacturer wants anchor bolts 75 to 100mm in from the wall line. If the wall is right on the slab edge, the bolts blow out the corner of the concrete when you drill or stress it when you tighten down.
The fix is simple: pour the slab bigger than the shed. The standard overhang in SEQ is 100mm minimum, 150mm preferred.
How Much Overhang? 100mm vs 150mm
Both are fine. The choice comes down to how much room you have and how much extra concrete you want to pay for.
| Overhang | Slab Size | Slab Area | Best For |
|---|---|---|---|
| 100mm each side | 6.2 x 9.2m | 57.04 m² | Tight blocks, lower cost, minimum acceptable spec |
| 150mm each side | 6.3 x 9.3m | 58.59 m² | Better runoff, easier anchoring, room for a doorstep |
The 150mm overhang only adds about 1.5 square metres of concrete (around 0.15 to 0.22 m³ depending on thickness), so it's cheap insurance. Most of the 6x9m slabs we pour in SEQ are 6.3 x 9.3m.
Slab Thickness for a 6x9m Colorbond Shed
A 6x9m shed is big enough that thickness matters a lot more than it does for a small garden shed. Here's how we spec it based on use.
| Shed Use | Thickness | Reinforcement | Notes |
|---|---|---|---|
| Empty storage only | 100mm | SL72 mesh | Boxes, garden tools, light gear. Minimum spec. |
| Storage with workbench and tools | 125mm | SL72 mesh | Hand tools, small stationary equipment, foot traffic. |
| Car, mower, trailer | 125mm | SL82 mesh | Wheel point loads need the heavier mesh. |
| Workshop with heavy machinery | 150mm | SL82 mesh | Lathes, drill presses, vehicle hoists, heavy stock. |
For more on the thickness decision, see our guide on how thick a shed slab should be. If your shed supplier has engineered drawings, we can pour to engineering specifications if your shed supplier provides them.
Edge Thickening for Larger Sheds
A 6x9m shed is in the size range where a flat slab can flex at the edges under load, especially on reactive clay soils. The fix is edge thickening, also called a thickened edge or a perimeter footing strip.
The edge thickening is a deeper band of concrete around the perimeter of the slab, usually 200 to 300mm deep and 200 to 300mm wide. It's poured monolithically with the rest of the slab, so it forms one continuous piece. The deeper edge spreads the load of the shed wall down into firmer ground and resists soil movement.
We recommend edge thickening on a 6x9m slab in three situations:
- Reactive clay soil: Common across Brisbane, Logan, Ipswich and Redlands. The deeper edge resists the soil swell and shrink cycle.
- Sloping or filled ground: Where part of the slab sits on cut and part on fill, the edge thickening helps the slab span any soft spots.
- Workshop or vehicle use: Heavier loads at the wall line (machinery on edge, vehicle parked near the door) benefit from the deeper edge.
Edge thickening adds 5 to 10 percent to the concrete volume and a similar amount to the labour cost. On a 6x9m slab it's almost always worth it.
Concrete Volume for a 6x9m Slab
Concrete volume is length times width times thickness, all in metres. For a 6.2 x 9.2m slab at the three common thicknesses:
| Thickness | Calculation | Raw Volume | Order (with waste) |
|---|---|---|---|
| 100mm | 6.2 x 9.2 x 0.1 | 5.7 m³ | 6.0 m³ |
| 125mm | 6.2 x 9.2 x 0.125 | 7.1 m³ | 7.5 m³ |
| 150mm | 6.2 x 9.2 x 0.15 | 8.6 m³ | 9.0 m³ |
The order volume includes 5 to 10 percent extra for waste: uneven ground, formwork thickness, spillage, and the small amount lost in the truck chute and cleanup. Running short on a slab this size is a disaster because you'll need a second truck and the joint between pours becomes a permanent weak spot.
If you've specced edge thickening, add another 0.4 to 0.8 m³ on top of the volumes above (the exact extra depends on the edge depth and width).
For the maths on a smaller slab, see how much concrete for a 6x4m shed slab.
Mesh Quantities for a 6x9m Slab
Standard mesh sheets in Australia are 6m x 2.4m, so each sheet covers 14.4 square metres. For a 6.2 x 9.2m slab (57 m²) with the standard 200mm overlap on the joins, you need about 5 sheets.
A practical layout: three sheets running the long way (the 9.2m direction) gives you 7.2m of coverage. Add two sheets crossways on the remaining 2m strip with overlap. You'll have offcuts, which is normal.
- SL72 mesh: Lighter mesh for storage slabs. Around $90 to $110 per sheet, so $450 to $550 for 5 sheets.
- SL82 mesh: Heavier mesh for vehicle and workshop slabs. Around $130 to $160 per sheet, so $650 to $800 for 5 sheets.
The mesh has to sit in the middle of the slab, not on the ground. Plastic bar chairs hold the mesh at the correct height as the concrete is placed. Mesh dragged up onto the wet concrete with a hook (called "hooking up") is a sign of a rushed job and gives you a slab with no effective reinforcement near the bottom or top.
Anchor Points: How Many for a 6x9m Shed
Colorbond and similar steel sheds in the 6x9m range typically have anchor bolts at every corner plus every 1.2 to 1.5m along the base rail. That works out to 10 to 14 anchor points for a 6x9m shed:
- 4 corners
- 6 to 8 along the two long (9m) walls
- 2 to 4 along the two short (6m) walls (some manufacturers skip the centre on short walls if the rail is stiff enough)
Anchor bolts can be cast in (set into the wet concrete during the pour) or drilled and chemically fixed after the slab cures. Cast-in is stronger and quicker but requires a precise shed pad-out plan before the pour. Drill-and-fix is more forgiving because you anchor after the shed is positioned exactly where you want it.
For a deeper dive, see how to anchor a shed to a concrete slab.
Drainage: Fall the Slab Away From the Shed
The slab needs a fall away from the inside of the shed to drain any water that does get in (from open doors, washing down equipment, condensation). The minimum fall is 1:100, or 10mm per metre.
For a 6x9m shed, that's a 60mm fall across the 6m width or 90mm across the 9m length. We usually fall the slab to the door end where the apron is. If the shed has a roller door at one end, fall the slab gently toward that door so water flows out, not back into the shed.
Outside the shed, the apron (the overhang) should fall away from the wall at 1:50 (20mm per metre) so rainwater drains off the slab and into the surrounding ground, not back under the wall sheets.
Brisbane Wind Zone for 6x9m Sheds
Most of Brisbane, Logan and Ipswich is wind region B (Region B), which covers most non-cyclonic areas of Queensland. A 6x9m Colorbond shed is large enough that the uplift loads in winds are significant, and the slab anchoring has to handle them.
Shed manufacturers usually supply an engineering certificate that specifies the slab thickness, mesh and anchor spec for the wind zone of your suburb. The certificate is what your council building approval will reference, and it's what we'll work to on the day. Double check the wind zone with your shed supplier before the slab is poured. If the supplier specs heavier anchoring than the defaults in this article, follow the supplier spec.
Coastal suburbs (Redlands, Wynnum, Sandgate, parts of the Gold Coast) sometimes fall into a higher wind zone and need cyclone-class anchoring.
What a 6x9m Slab Costs in Brisbane and SEQ
As an indicative starting guide, here's what a finished 6x9m Colorbond shed slab (around 57 square metres) typically costs in Brisbane and SEQ on a good access site.
| Spec | Thickness and Mesh | Starting From |
|---|---|---|
| Storage slab | 100mm, SL72 | $4,800 |
| Storage with workbench | 125mm, SL72 | $5,500 |
| Vehicle slab | 125mm, SL82 | $5,800 to $7,000 |
| Workshop slab | 150mm, SL82 | $7,500 |
Costs go up for sloping sites, poor access (rear yards, narrow side gates that block a concrete truck), heavy excavation, edge thickening, exposed aggregate or coloured finishes, and after-hours pours. For the full breakdown, see our pricing guide.
What Sets a Good 6x9m Slab Apart
Anyone with a vibrator and a screed bar can pour 8 cubic metres of concrete. A slab that's still flat, level and crack-free in 10 years is a different job. The things that matter on a 6x9m slab:
- Dead level surface: A 6x9m slab covers 57 square metres. Any high or low spots show up immediately as a wobble in the wall sheets or a roller door that won't seal. We use laser levels on slabs this size, not just string lines.
- Proper edge protection: Clean, sharp slab edges with a slight radius (called arrising) stop the corners chipping when the shed is being erected. Edge thickening adds structural strength.
- Mesh in the middle, not on the ground: Bar chairs every 600mm hold the mesh at the right height. Mesh sitting on the ground does almost nothing structurally.
- Right anchor points: Cast-in bolts have to be in the right spot to the millimetre, or drilled-and-fixed anchors have to land on solid concrete (not on a mesh wire, and not too close to the edge).
- A proper base under the slab: 75 to 100mm of compacted road base on a prepared subgrade. Slabs that sit on uncompacted fill or soft clay crack within a year.
For more on the base under the slab, see what base is needed under a concrete slab.
Get a Real Quote for Your 6x9m Slab
If you've got a 6x9m Colorbond shed coming and you want a fixed price for the slab, get in touch. We'll come out, check access, slope, soil and the shed supplier's drawings, and give you a written quote. We pour 6x9m slabs across Brisbane, Logan, Ipswich, Redlands, Caboolture and the Gold Coast.
For the full service details, see our shed slabs page, or use our calculator for a quick volume and cost estimate.
Important Disclaimer
All prices are indicative starting-from guides only. Final pricing depends on site conditions, access, soil type, and specific requirements.
Thickness, mesh and anchor recommendations in this article are general guidance based on standard practice for 6x9m Colorbond and similar steel sheds in SEQ. Always follow the engineering specifications supplied by your shed manufacturer for your specific wind zone and site. We can pour to engineering specifications if your shed supplier provides them. We specialise in small concrete jobs only, including shed slabs, garage slabs, concrete footpaths, concrete pads, and water tank slabs.
Frequently Asked Questions
As an indicative guide for Brisbane and SEQ, a finished slab for a 6x9m Colorbond shed (around 57 square metres at 6.2 x 9.2m) starts from about $4,800 at 100mm with SL72 mesh and a broom finish on a good access site. Stepping up to 125mm with SL82 mesh for vehicle storage typically starts from around $5,800 to $7,000. Workshop spec at 150mm starts from around $7,500. Final pricing depends on site conditions, access, soil type, and specific requirements. See our pricing guide for the full breakdown.
A 6x9m slab is a one day pour for an experienced crew on a prepped site. Site prep, formwork, base compaction and mesh placement usually take one to two days before the pour. On pour day, the concrete is placed, screeded, floated and finished over about 4 to 6 hours from the time the first truck arrives. The slab is walk-on the next day but you should wait 7 days before erecting the shed and 28 days before driving any vehicle onto it.
A 6x9m Colorbond shed has a 54 square metre footprint, which is over the 10 square metre exempt size in most Brisbane councils and well over 2.4m tall, so the shed itself almost always needs building approval. The slab is part of that approval. Check with your local council (Brisbane City, Logan, Ipswich, Moreton Bay, Redland or Gold Coast) before you start. Your shed supplier or a private certifier can lodge the application for you.
For storing a car, mower or trailer in a 6x9m Colorbond shed, we recommend 125mm thickness with SL82 mesh. The extra 25mm over a standard 100mm slab gives you the load capacity for vehicle weight and the heavier SL82 mesh resists cracking from the point loads of tyres. If you'll be parking heavier vehicles like a 4WD with trailer, or running a workshop with machinery, step up to 150mm with SL82 mesh. For more, see how thick should a shed slab be.
No. The slab should be 100 to 150mm larger than the shed footprint on each side. So a 6x9m Colorbond shed should sit on a 6.2x9.2m slab minimum, and 6.3x9.3m is even better. The overhang stops rainwater running back under the wall sheets, protects the slab edge from chipping, and gives you a clean surface to anchor the shed base rail into. Pouring an exact 6x9m slab and lining the walls up with the edge causes problems that show up within a year.