The Short Answer: It Depends
Do you need footings for your shed slab? The answer is: it depends on the shed size, soil type, location in Queensland, and how the slab will be used. For most small residential sheds in Brisbane, a well-designed concrete slab with proper subgrade preparation is sufficient – no footings required. But for larger sheds, poor soil conditions, or structures in cyclone zones, footings become necessary.
This guide explains what footings are, when you need them, and how Queensland conditions affect the decision.
What Are Footings and Why Do Shed Slabs Need Them?
Footings are structural elements that support and distribute the weight of a building safely into the ground. For shed slabs, "footings" typically refer to thickened edge beams or deeper support structures around or beneath the perimeter of the slab.
Why Footings Matter
A slab alone sits on the surface. Footings extend deeper into stable soil, which:
- Distributes concentrated loads – shed frame corners and walls press heavily on the slab edge; footings spread this load over more soil
- Prevents edge heave and subsidence – in reactive soils, edges move more than the centre; footings stabilize edges
- Provides secure anchoring – strong footings hold framing anchors firmly
- Protects against soil movement – reactive clay movement affects edges first; footings go deeper into more stable soil
When Are Footings Required for Shed Slabs?
Larger Sheds (Over 6x6m or 36m²)
Bigger structures generate larger concentrated loads at corners and along edges. A small 3x3m tool shed might not need footings, but a 9x6m shed with machinery or a 12x6m workshop should have them. Size alone often triggers the need for footings.
Poor or Reactive Soil Conditions
If soil testing reveals highly reactive clay, soft spots, or unstable subgrade, footings become essential. They bridge unstable soil and anchor the slab into deeper, more stable layers. Brisbane's reactive clays often require footings for peace of mind, especially in larger or heavier sheds.
Cyclone Zones and High Wind Areas
In QLD cyclone zones (coastal areas and some inland regions), wind loads on larger sheds are extreme. Footings provide anchoring to resist uplift and lateral forces. If your property is in a cyclone zone and you're building a substantial structure, footings are often specified or recommended.
Vehicle or Heavy Machinery Use
If vehicles will regularly park on or drive across the slab, or if heavy machinery will operate on the surface, footings help distribute those loads safely. A light storage shed is different from a shed that houses a workshop or car port.
Long-Term Settlement Concerns
If the site has history of settlement issues, soft ground, or poor drainage, footings provide stability where a slab alone might settle unevenly. Uneven settlement can crack a slab; footings prevent this.
Types of Footings for Shed Slabs
Edge Beams (Thickened Edges)
The simplest option: a slab that is thicker around the edges (typically 100mm main slab with 150-200mm edge beams running the perimeter). This adds strength and stability at the critical edge zones where loads concentrate. Edge beams are cost-effective and suitable for many sheds. They're not "footings" in the traditional sense but provide significant edge support.
Strip Footings
A concrete strip (typically 300-400mm wide, 400-600mm deep) runs beneath the planned walls or perimeter of the slab. The slab sits on top of this thickened strip. Strip footings extend into deeper, more stable soil and anchor the structure effectively. They're the standard for medium-sized sheds (6x6m to 12x12m range) and are commonly used in reactive clay areas.
Pad Footings
Individual pads (square concrete blocks) placed under each corner or post location. These work well for small sheds where loads are concentrated at specific points. A small garden shed might only need pad footings at four corners, not a continuous footing. Pad footings are economical for light structures.
Deep Footings (Piers)
For severely reactive clay, very soft soil, or specialized applications, footings might extend 1m or deeper to reach stable soil layers. These are rare for residential sheds and significantly increase cost. They're only used when other options are insufficient.
QLD-Specific Considerations for Shed Footings
Reactive Clay Soil Classification
Queensland has an established soil classification system for reactive clays. Soils are rated H1 to H5, where H5 is extremely reactive. Brisbane soils are typically H2 to H4. As the reactivity rating increases, the structural requirements – including footings – become more stringent. An H1 soil might need no special footings; an H4 almost certainly needs them.
Cyclone Wind Categories
QLD is divided into cyclone wind categories (C1, C2, C3, C4). Coastal and some inland areas are C3 or C4, meaning extreme wind loads. Larger sheds in these zones require robust footings to anchor them against uplift and lateral forces. Check your property's wind category – it directly affects footing requirements.
Brisbane's Reactive Clay Challenge
Brisbane is notorious for reactive clay. The standard guidance is: if your property is in Brisbane or the surrounding suburbs, assume reactive clay unless proven otherwise. Reactive clay expands in wet seasons (October through March) and shrinks in dry seasons – this movement is worst at edges. Footings that extend below the zone of soil movement are essential for long-term stability.
Seasonal Rainfall Patterns
Brisbane's intense wet season (November-April) saturates clay soils. The dry season (May-October) dries them out. This annual cycle puts stress on structures. Footings that extend into soil below this seasonal moisture change zone prevent problems. Proper drainage around footings is equally important.
Understanding Brisbane's Reactive Clay
This is critical for the footings question. Brisbane's clay is reactive – it contains minerals (smectite) that swell when wet and shrink when dry. The top 1-2m of soil experiences significant seasonal movement.
What does this mean for footings?
- A slab sitting on the surface (with shallow footings) moves with the clay as it swells and shrinks
- The slab edge moves more than the centre – edges can heave or subside relative to the centre
- This movement causes cracking and structural problems
- Footings extending below the active clay zone (1.5-2m depth) reach stable soil
For small sheds, thicker concrete and good edge beams manage this movement reasonably well. For larger or more critical structures, traditional footings that extend deeper into stable soil are the proper solution.
Cost Difference: With and Without Footings
Do footings significantly increase cost? It depends on the type:
- Edge beams only: +10-20% on slab cost (just thicker concrete at edges)
- Strip footings: +25-40% on slab cost (significant excavation and concrete)
- Pad footings: +15-30% depending on number and depth
- Deep footings/piers: +50-100%+ (major cost addition)
For a typical 6x6m shed slab costing $2,400-$3,200, adding edge beams might be $300-$600 extra, while strip footings might add $600-$1,200. It's a real cost, but for structural security, it's often worthwhile.
How to Know If Your Shed Needs Footings
The right way to determine this is through professional site assessment:
Step 1: Know Your Shed Size
Measure the planned dimensions. Larger structures are more likely to need footings.
Step 2: Identify Soil Type
Brisbane = assume reactive clay unless you have a soil report showing otherwise. If you have a soil report (from building inspection or prior construction), refer to the reactivity classification.
Step 3: Check Wind Category
Look up your property's cyclone wind category online through QLD government resources. C3 or C4 = footings likely needed for larger sheds.
Step 4: Assess Site Conditions
Are there signs of soil movement? Cracked driveways, uneven ground, or poor drainage? These suggest footings should be specified.
Step 5: Get Professional Assessment
Contact us for a site assessment. We'll evaluate your specific situation and recommend the appropriate foundation solution – whether that's edge beams, strip footings, pad footings, or a combination. This assessment is part of getting an accurate quote.
QLD Standards and Best Practice
We design shed foundations following:
- AS3600 (Australian Standard for Concrete Structures)
- AS1170 (Wind Load Standards) for cyclone areas
- Queensland Building & Construction Commission guidelines for reactive clay management
- Local council requirements where applicable
For reactive clay soils (which includes Brisbane), the guidance is clear: deeper foundation support is preferable to shallow solutions. For larger structures, footings are specified as best practice.
Getting the Right Footing Solution for Your Shed
Don't guess – get professional advice. When you contact us:
- Tell us your shed dimensions and intended use
- Provide your address (we can identify soil type and wind category)
- Describe site conditions (flat, sloping, wet, well-drained, etc.)
- Let us assess the site
We'll recommend the most cost-effective solution that meets safety standards for your specific situation. That might be simple edge beams for a small shed, or proper strip footings for a larger workshop. Either way, the recommendation will be site-specific and justified.
Check out our Pricing Guide for more information, or Contact us to discuss your shed project.
Important Disclaimer
All footing recommendations in this article are informational guides. Actual footing requirements depend on soil assessment, structure size, intended use, local wind exposure, and site-specific conditions. Always obtain a professional site assessment for your project.
Not a licensed builder. We specialize in small concrete jobs only – shed slabs, garage slabs, concrete footpaths, and small pads. We do not construct house slabs, design structural systems, or provide engineering certification. Always consult with appropriate professionals for your specific project needs.
Common Questions About Shed Slab Footings
No, not necessarily. Small, light sheds (under 4x4m) with minimal load might be fine with a well-designed slab and good edge support. Larger sheds, workshops with machinery, or structures in cyclone zones almost certainly benefit from footings. A site assessment determines what's appropriate for your specific project.
Edge beams are part of the slab – a thickened edge (same slab depth with a thicker edge zone). True footings extend below the slab into deeper, stable soil. Edge beams improve edge support but don't go deep. Strip footings extend 400-600mm below the slab surface. For Brisbane's reactive clay, strip footings are more effective than edge beams alone.
Typical shed slab footings in Brisbane are 400-600mm deep – deep enough to extend below the active zone of reactive clay soil movement (typically the top 1-2m). Very large sheds or poor soil might require deeper footings (800mm-1m+). Depth is determined by soil conditions and structure size. Your site assessment will specify the appropriate depth.
Not really. Footings are built during the slab construction. Adding them later would require underpinning – breaking into the slab, excavating, and building footings underneath – which is expensive and disruptive. It's much better to get it right the first time. If you're unsure, err on the side of proper footings during initial construction.
In Brisbane's reactive clay, yes. A slab without proper footings often cracks within 10-15 years due to soil movement, especially at edges. A properly footed slab resists this movement and can last 30+ years with minimal maintenance. Footings are an investment in longevity and peace of mind.