Why Your Shed Foundation Matters
Your foundation is the most critical part of any shed build. Get it wrong and you’ll deal with cracking, shifting, water pooling, and structural problems for the life of the building. Get it right and your shed will perform exactly as engineered for decades.
For steel frame sheds, the foundation must match the engineering specifications. Every Shedz kit comes with site-specific engineering drawings that specify exactly what your slab or footings need to look like, including dimensions, reinforcement, hold-down bolt locations, and concrete strength.
Types of Shed Foundations
Concrete Slab on Ground
The most common foundation for steel sheds in Australia. A reinforced concrete slab provides a level, durable surface that doubles as your floor. Typical specifications:
- Thickness: 100mm for residential sheds, 150mm+ for heavy vehicle or industrial use
- Concrete strength: N25 or N32 depending on engineering requirements
- Reinforcement: SL82 or SL72 mesh, with additional reinforcement at edges and thickenings
- Edge beam: typically 300mm x 300mm with N12 reinforcing bars
- Hold-down bolts: cast into the slab at precise locations matching your frame layout
Important: Always refer to your signed-off engineering drawings for the concrete slab and footings design and specifications for your specific shed. The above are general guidelines only, your engineer’s specifications take priority.
Pier Footings
Pier footings (also called pad footings or post footings) are individual concrete pads poured at each column location. They’re common for:
- Sloping sites where a full slab isn’t practical
- Rural properties where a gravel or earth floor is preferred
- Farm sheds where machinery needs to drive in and out
- Budget-conscious builds where you want to minimise concrete costs
Each pier is typically 600mm x 600mm x 600mm deep, with hold-down bolts cast in. Your engineering drawings will specify the exact size and depth based on your soil classification and wind loads.
Strip Footings
A continuous strip of concrete along the shed walls. Less common for standard sheds but sometimes used for livable shed homes where the wall loads are distributed along the entire length.
Site Preparation
Before any concrete is poured, your site needs to be prepared:
- Soil test: a geotechnical report classifies your soil (A, S, M, H, E, or P class). This determines your footing design.
- Clearing and levelling: remove vegetation, topsoil, and level the pad area
- Compaction: compact the sub-base to the required density
- Drainage: ensure water drains away from the slab. Consider ag-pipe around the perimeter.
- Services: if your shed needs water, sewer, or electrical, run the pipes and conduits before the slab is poured
Getting the Hold-Down Bolts Right
This is where most DIY slabs go wrong. Hold-down bolts must be placed at exact positions matching your steel frame layout. Even 10mm out and you’ll have problems bolting down the columns.
Tips for getting it right:
- Use a template or jig, many shed suppliers provide bolt layout drawings
- Double-check dimensions before the pour, measure diagonals to ensure square
- Set bolts to the correct height, too low and the thread won’t engage, too high and the baseplate won’t sit flat
- Protect bolt threads during the pour, wrap with tape or use bolt caps
Cost Guide
Concrete slab costs vary significantly based on site conditions, location, and concrete prices in your area. As a rough guide:
- Small residential shed (6m x 6m): $3,000 to $6,000
- Medium shed (12m x 9m): $8,000 to $15,000
- Large farm/commercial shed (18m x 12m+): $15,000 to $30,000+
These figures include excavation, formwork, reinforcement, concrete supply, and finishing. Add 20 to 30% for difficult sites (slope, rock, poor access).
Choosing a Concretor
For owner builders, the slab is one job worth getting a professional for. Look for:
- Experience with shed slabs (not just house slabs, the bolt layouts are different)
- Willingness to work from your engineering drawings
- A clear quote that itemises concrete volume, reinforcement, and finishing
- Insurance and licensing appropriate for your state
Need help planning your shed foundation? Contact Shedz and we’ll provide the engineering drawings your concretor needs to get it right first time.
