The foundation is the most permanent decision you’ll make about a shed. Get it wrong and you’ll deal with an unlevel floor, structural movement, and potentially drainage problems for the life of the shed.

Australia’s building codes and local council regulations vary significantly on foundation requirements, but there are three main foundation types used for residential sheds: concrete slabs, pier foundations, and timber skids. Each has advantages and appropriate use cases.

Here’s what you need to know to choose the right foundation for your shed.

Concrete Slab Foundation

A concrete slab is a continuous reinforced concrete pad that the shed sits on. It’s the most common foundation type for permanent sheds in Australia.

How it’s built:

1. Site is excavated and leveled
2. Compacted gravel or crushed rock base (100-150mm)
3. Plastic vapour barrier
4. Reinforcing mesh (SL82 or similar)
5. Concrete poured to thickness (typically 100mm for sheds, 125mm+ for larger structures)
6. Finished with a broom or troweled surface

Advantages:

• Provides a level, permanent floor
• No separate flooring needed
• Prevents ground moisture and pests entering the shed
• Distributes load evenly—suitable for heavy equipment or vehicles
• Complies with most council requirements for permanent structures
• Longest lifespan (50+ years with minimal maintenance)

Disadvantages:

• Most expensive option ($3,000-8,000 depending on size and site conditions)
• Requires excavation, formwork, and concrete truck access
• Permanent—can’t be moved if you change your mind about shed location
• Usually requires council approval and engineering if the shed is over a certain size (varies by council, typically 10m²+)
• Not suitable for significantly sloped sites without extensive excavation

When to use:

• Permanent sheds that will stay in one location
• Sheds housing vehicles, heavy equipment, or machinery
• Areas with council regulations requiring concrete for structures over a size threshold
• Sites where you want a finished floor without additional flooring materials

Cost: For a 6m x 3m shed, expect $3,500-6,000 for a properly prepared and poured slab including base, mesh, and finishing. Prices increase significantly if the site needs extensive leveling or if access is difficult.

Pier Foundation (Post and Pad)

Pier foundations use individual concrete footings at strategic points under the shed’s frame. The shed sits on a timber or steel frame supported by these piers.

How it’s built:

1. Mark pier locations (typically at each corner and at 1.5-2m intervals along walls)
2. Dig holes 300-450mm diameter, 600-900mm deep (below frost line and stable soil)
3. Pour concrete footings
4. Place galvanized stirrups or post brackets in wet concrete
5. Install timber or steel bearers between piers
6. Shed frame bolts to bearers

Advantages:

• Much cheaper than full slab ($800-2,000 depending on number of piers)
• Works well on sloped sites—piers can be different heights to create a level platform
• Less excavation and site disturbance
• Sometimes avoids council development approval if the shed remains “non-permanent” (varies by council)
• Can be removed or relocated more easily than a slab

Disadvantages:

• No floor included—you need to add timber, steel, or composite decking
• Not as stable as a slab for heavy loads concentrated in one area
• Requires protection from ground moisture (timber must be treated, steel must be galvanized)
• Pests (rodents, snakes) can access under the shed
• Annual maintenance checking for level and stability

When to use:

• Sloped sites where a slab would require massive excavation
• Budget-conscious builds where a slab is too expensive
• Temporary or relocatable sheds
• Sheds in areas where drainage and ventilation under the floor is beneficial

Cost: For a 6m x 3m shed, expect $1,200-2,500 including piers, bearers, and basic timber flooring. Less if you’re handy with concrete and do the work yourself.

Timber Skid Foundation

Skids are treated timber beams (typically 200mm x 75mm or larger) laid directly on compacted ground or a gravel base. The shed sits on these skids.

How it’s built:

1. Level the site and compact soil
2. Lay compacted gravel base (50-100mm)
3. Place treated timber skids parallel to each other, typically 1.2-1.5m apart
4. Check for level using a long spirit level or laser level
5. Shed frame bolts or brackets to skids

Advantages:

• Cheapest foundation option ($300-800 in materials)
• Quickest to install (can be done in a day)
• Truly temporary—can be picked up and moved with the shed
• Often doesn’t require council approval (check local regulations)
• Good drainage—shed sits slightly above ground

Disadvantages:

• Least stable—can shift over time, especially on clay soils or in high wind
• Timber will eventually rot even if treated (10-15 year lifespan typical)
• Not suitable for heavy loads or large sheds
• May not comply with council requirements for permanent structures
• Wildlife can nest under the shed

When to use:

• Small sheds (under 10m²)
• Temporary storage needs
• Rental properties where you may need to remove the shed later
• Budget builds where cost is the primary concern
• Well-draining sandy or gravelly sites

Cost: For a small shed (3m x 2m), expect $400-800 including treated timber skids and gravel base. This is the only foundation type where DIY is genuinely straightforward for most people.

Council Approval and Regulations

Foundation requirements are often tied to council development approval regulations.

General patterns (check your local council):

• Sheds under 10m² often exempt from approval—skids or piers acceptable
• Sheds 10-25m² typically require approval but not always engineering—piers or slab required
• Sheds over 25m², or within 1m of boundaries, or used for habitation—full approval and engineering required, typically mandating a slab

Engineering requirements: Many councils require a structural engineer to certify foundations for sheds over a certain size or in areas with specific soil conditions (reactive clay, fill, coastal sand). This adds $500-1,500 to costs but ensures the foundation won’t fail.

Bushfire-prone areas: In BAL (Bushfire Attack Level) rated areas, councils often mandate concrete slabs with specific ember protection requirements. Timber skids are generally not permitted.

Flood-prone areas: Some councils require sheds to be elevated on piers to minimum heights above the 1-in-100 year flood level.

Check your council’s planning scheme and talk to the building department before committing to a foundation type.

Soil Type Considerations

Clay soils: Reactive clay swells when wet and shrinks when dry. This movement can crack slabs or shift piers. If you’re building on clay, you need:

• Deep piers below the reactive zone (often 600-900mm)
• Reinforced slabs with thickened edges
• Possibly engineered foundation design

Sandy soils: Drain well but may not provide stable bearing. Piers need to be wider at the base (belled footings) to prevent sinking.

Rocky sites: Difficult to dig but very stable. Piers may require rock-breaking equipment or shallower footings if you hit bedrock.

Fill sites: If your site has been filled, you need to know what’s underneath. Poorly compacted fill will settle over time. Piers should extend through fill to natural ground, or the fill needs professional compaction.

Get a soil test if you’re building a large shed or if the site has obvious issues (cracking existing structures, standing water, very soft or hard ground).

My Recommendations

For most suburban permanent sheds (6m x 3m workshop or storage): Concrete slab. Yes, it’s $3,500-6,000, but you get a level, finished floor, no maintenance, and it meets council requirements. The upfront cost is worth the permanence and usability.

For sloped sites or budget builds under 10m²: Pier foundation with timber floor. Much cheaper than a slab, works on slopes, and adequate for light to moderate use.

For temporary or very small sheds (garden sheds, tool storage): Timber skids on gravel. Cheap, quick, movable. Accept that it’s not a permanent solution.

For heavy machinery or vehicle storage: Engineered concrete slab, possibly 125mm thick with additional reinforcing. Don’t compromise on foundation if you’re parking a car or storing heavy equipment.

Common Foundation Mistakes

Skipping site preparation: Pouring concrete on soft, uncompacted ground leads to cracking and settlement. Proper base preparation (compacted gravel) is essential.

Inadequate reinforcing: Using too little mesh or no mesh in a slab means it will crack under load or soil movement.

Ignoring drainage: If water pools around your shed, it will undermine piers or erode under slabs. Grade the site so water flows away.

DIY concrete without experience: Pouring a slab looks simple but getting level, proper finish, and correct curing is harder than it appears. Unless you have concrete experience, hire professionals.

Not checking level during construction: Once concrete sets, you’re stuck with whatever level you poured. Check multiple times during the pour.

The Bottom Line

Foundation choice comes down to permanence, budget, site conditions, and council requirements. For most people building a standard backyard shed in a suburban setting, a concrete slab is the right answer despite the higher upfront cost.

If cost is tight or the site is sloped, piers are a solid compromise. If you’re building something small and temporary, skids work fine.

Don’t skimp on the foundation to save a few hundred dollars on a $5,000-10,000 shed. The foundation is the most permanent part—get it right the first time.