Perth shed slabs & concrete slabs price bands
| Band | $/m² (supplied and installed) | What puts a job in this band |
|---|---|---|
| Low | $85–$105 / m² | Garden shed slab, 100mm thick, SL72 mesh, level Bassendean-sand ground with good access. Under 25m². Common for backyard sheds in Baldivis, Alkimos and Wellard new estates. |
| Mid | $105–$130 / m² | Larger workshop or double-garage slab, 125mm thick, SL82 mesh, thickened edge beam, formwork around a level site. 25–60m². Most common band for Perth suburban shed pours. |
| High | $130–$150 / m² | Granny flat pad or heavy-vehicle workshop, 150mm slab with engineered mesh and edge beam, deep base prep on reactive clay, complex forms. 60m²+. Common in eastern-corridor suburbs with clay ground. |
What drives the cost in Perth
Slab thickness
100mm suits sheds and light workshops. 125mm suits a double garage or workshop with a car hoist. 150mm suits a granny flat, heavy vehicle workshop, or anywhere a slab-on-ground foundation is doing structural work. Every extra 25mm adds roughly 8–12 per m².
Mesh grade
SL72 is the residential default. SL82 (heavier bars, closer spacing) handles heavier loads and reduces cracking on reactive ground. F72 (two-way bar mesh) is used on engineered slabs for habitable structures. Bar chairs to keep mesh at mid-slab are non-negotiable — mesh sitting on the base does nothing structurally.
Edge beam
A thickened edge beam (300mm deep, 300mm wide) around the slab perimeter transforms it from a floating pad into a footing-integrated slab. Required for granny flats and habitable structures; strongly recommended for garages. Adds roughly $60–$90 per linear metre of perimeter.
Ground conditions
Bassendean sand (coastal plain, Alkimos to Golden Bay) needs 100mm of compacted road base under the slab. Reactive Guildford clay (Ellenbrook, Aveley, Byford) needs deeper prep with a controlled sub-base to prevent slab curl. Ground survey and, on clay, an engineer's slab design may be needed for anything over 30m².
Access and pour method
Direct truck access to the pour location is cheapest. A concrete pump is often required for backyard shed slabs and adds $700–$1,200 for the day but preserves consistency across the pour. Wheelbarrow-only access adds labour and slows the pour to a level where finishing suffers.
Process
- 1
Site prep and excavation
Strip topsoil and organic matter down to firm subgrade. For a 100mm slab plus 100mm base, that's 200mm below the finished surface level. Check underground services — Perth suburbs commonly have shallow reticulation lines to remove or reroute.
- 2
Base preparation
Lay and plate-compact 100mm of road base in two lifts. Achieve at least 95% density. On reactive clay, add a moisture-controlled sub-base layer as specified. On sand, single lift can be sufficient but doesn't cost much more to do properly.
- 3
Formwork and services
Set formwork to the finished level with appropriate fall for drainage. Install underground services rough-ins (drainage, power conduit, water) before the pour. Set the edge beam trench if specified. Position tie-downs for shed anchorage.
- 4
Reinforcement
Lay a plastic vapour barrier over the base. Position mesh on 40mm bar chairs. Overlap mesh sheets by at least 225mm and tie every second intersection along the overlap. For edge beams, add horizontal bars in the beam trench.
- 5
Pour and finish
Pour a 25 or 32 MPa mix depending on end use (32 MPa for workshops with hoists). Screed level, bull-float, then broom-finish for grip or steel-trowel for a smoother surface. Saw-cut control joints on slabs over 25m² within 24 hours.
- 6
Cure
Damp-cure for 7 days minimum — hessian and plastic in summer, plastic alone in winter. Walk on it after 24 hours; drive on it after 7 days; full loading after 28 days when the slab reaches design strength.
Perth-specific considerations
- For sheds installed on the slab, check the shed manufacturer's spec for tie-down locations before you pour. Post-drilling tie-downs into cured concrete costs more than casting the tie-downs in place.
- Perth new-estate blocks are often delivered with a builder's spoil layer that looks like clean fill but isn't. Test-dig before pricing — you may need to remove 300mm of dodgy fill to reach firm subgrade.
- The reactive Guildford clay in Ellenbrook, Aveley and Byford causes slab movement that will crack an under-designed shed slab within two summers. Insist on SL82 mesh and an edge beam on clay ground even for 'just a shed'.
- Coastal salt exposure in Alkimos and Golden Bay attacks reinforcement mesh if the concrete cover is inadequate. Bar chairs are mandatory — no mesh sitting on the base 'because it'll rise up during the pour'.
- For workshops with car hoists, insist on 150mm slab thickness and 32 MPa mix. A hoist point-loads the slab beyond what a standard garage floor is designed for.
Compare with the alternatives
Driveways vs shed slabs
Driveways carry rolling loads and need saw-cut joints roughly every 3–4m to control shrinkage cracking. Shed slabs carry static loads under a covered structure and often don't need joints on smaller pours. Same base construction; different finish and jointing.
Read more →Alfresco slabs
Alfrescos are visually finished slabs — often exposed aggregate, honed or liquid-limestone-topped. Shed slabs are structural, often broom-finished under a covered shed floor. The base construction is similar but the finishing and detail work is very different.
Read more →Ready for a shed slabs & concrete slabs estimate?
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Frequently asked questions
How much does a shed slab cost in Perth?
A standard 6m×3m (18m²) garden shed slab costs $1,800–$2,700. A 6m×6m (36m²) double-garage slab with proper reinforcement runs $4,300–$5,400. Large granny-flat pads or workshop slabs on reactive clay ground can reach $12,000–$18,000.
How thick should a shed slab be?
100mm for garden sheds and light workshops. 125mm for double garages and workshops with light vehicles. 150mm for granny flats, heavy vehicle workshops, and anywhere a car hoist will be installed. Anything under 100mm is not a shed slab — it's a footpath.
Do I need council approval for a shed slab in Perth?
Not for the slab itself. The shed structure that sits on it may need a building permit depending on size and your LGA — most councils exempt sheds under 10m² and require a permit above that. Confirm with your local council before starting.
How long before I can build the shed on the new slab?
You can start assembling the shed frame after 7 days if the slab has been damp-cured. Wait 28 days before torquing anchor bolts to their full spec — the concrete only reaches design strength at 28 days.
Can a shed slab be poured on reactive clay ground?
Yes, with proper design. On the Guildford clay through Ellenbrook and the eastern corridor, insist on 125mm slab thickness minimum, SL82 mesh, thickened edge beam, and deeper base prep. Get an engineer's slab design for anything over 30m² on clay ground — cheaper than repairing a cracked slab in year three.
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