One of the first decisions when planning a shed is what to put under it. Concrete slab or timber floor on stumps? Both work, but they have different cost profiles, durability characteristics, and suitability for Brisbane conditions.

I’ve worked in sheds with both foundations, and I’ve helped enough people make this decision to have opinions about which works better in different situations.

Concrete Slab Advantages

Slabs handle heavy loads without flex. If you’re planning a workshop with heavy machinery—table saw, planer, lathe—a solid concrete floor provides stable footing. Precision equipment works better on non-flexing surfaces.

Durability is excellent. A properly poured slab lasts decades without maintenance. No concerns about rot, termites, or structural degradation that timber floors face.

For vehicle storage or workspace where you’re rolling heavy items around, concrete wins. You can wheel equipment freely without worrying about floor strength. Oil spills and chemical exposure don’t damage concrete the way they can damage timber.

Concrete provides some thermal mass that moderates temperature swings. In Brisbane summer, slab stays cooler than air temperature during the day. This helps slightly with keeping the shed comfortable.

Concrete Slab Disadvantages

Cost is higher. A professionally poured slab for a typical 6m x 4m shed runs $3500-5500 depending on site conditions, thickness, and finish quality. That’s before the shed structure goes up.

Site preparation requirements are more extensive. The ground needs to be level, properly compacted, and have adequate drainage. Sloping sites require more earthwork and potentially retaining walls.

Permanence is a double-edged sword. Once you pour a slab, the shed location is fixed. If you decide to move or reconfigure later, you’re working around an immovable concrete pad.

Moisture can be an issue on poorly draining sites. If the ground stays wet, moisture can wick through concrete and create humidity problems inside the shed. Vapor barriers under slabs help but aren’t always installed.

Timber Floor Advantages

Lower upfront cost is the big one. A timber floor on stumps for the same 6m x 4m shed costs $1500-2500 in materials and labor. That’s $2000-3000 less than a slab.

Works better on sloping sites. Rather than extensive earthwork to level for a slab, you adjust stump heights to create a level floor. This can save thousands on difficult sites.

Airflow under the floor helps with drainage and ventilation. In Brisbane’s wet season, having air circulation under the shed keeps moisture from accumulating. This is particularly valuable if you’re storing tools or equipment that rust.

Flexibility matters if you might want to relocate the shed later. A shed on stumps can theoretically be moved if needed. A shed on a slab is staying put.

Access underneath the floor is handy for running electrical conduit or plumbing if needed. You can fish cables under the floor without having to run conduit exposed on walls.

Timber Floor Disadvantages

Maintenance is ongoing. Timber in contact with ground (even treated timber) degrades over time. Expect to replace stumps or bearers eventually—maybe 15-20 years if you use quality treated timber, less if you cheap out.

Termites are a concern in Brisbane. Termite barriers and shields help, but timber in contact with ground is inherently attractive to termites. Regular inspections are necessary.

Floor flex affects precision. Heavy machinery on a timber floor can cause noticeable deflection. This matters for equipment requiring stable surfaces. Beefier framing reduces flex but increases cost.

Load capacity is lower than equivalent slab. If you’re storing very heavy items or planning to park a vehicle in the shed, timber floor might not be adequate without significant structural reinforcement.

Brisbane-Specific Considerations

Our clay soils have significant movement with moisture changes. They expand when wet, shrink when dry. Slabs need proper preparation and reinforcement to handle this movement without cracking.

Wet season drainage is critical for both options. A poorly draining slab ends up with water pooling around it and potentially undermining supports. A timber floor on a site with poor drainage might have stumps sitting in mud.

Termite pressure in Brisbane is high. This makes timber floors riskier than in cooler climates with less termite activity. Physical termite barriers and regular inspections are essential.

What Actually Works Best

For workshop sheds with heavy equipment: Slab is worth the extra cost. The stability and load capacity pay off if you’re serious about precision woodworking or metalwork.

For general storage sheds: Timber floor is cost-effective and adequate. Unless you’re storing something absurdly heavy, timber floor handles normal shed uses fine.

For vehicle parking: Slab is the right choice. The higher load capacity and hard surface work better for vehicles.

For sites with slope: Timber floor avoids expensive earthwork. Unless the shed use specifically requires a slab, use stumps and save the money.

For maximum longevity with minimal maintenance: Slab wins. Pay more upfront, don’t worry about floor maintenance for decades.

Hybrid Options Exist

Some people do a partial slab—pour concrete where heavy equipment will sit but leave the rest as timber floor. This gives you stable equipment bases without the cost of full slab.

Compacted gravel or road base under timber floor provides better drainage and termite resistance than setting stumps directly in soil. It’s a middle ground between full slab and basic stumps.

Composite or engineered timber products offer better termite and moisture resistance than traditional treated pine. More expensive but longer-lasting for critical structural elements like bearers.

Council Requirements

Brisbane City Council generally doesn’t care which foundation type you use for typical sheds, but there are requirements for both.

Slabs need adequate thickness (typically 100mm minimum), reinforcing mesh, and vapor barrier for habitable spaces. For sheds, requirements are less stringent but still exist.

Stumps need to be correctly sized and spaced based on floor span and load. Footings at each stump might be required depending on soil type and shed size.

For any shed over 10sqm or any shed on sloping land, check specific requirements with council before committing to a foundation type. Rules vary by zone and specific site conditions.

My Actual Recommendation

For a typical 6m x 4m workshop shed on relatively flat Brisbane block: I’d do timber floor if budget is limited, slab if you can afford it and plan to use the shed seriously for years.

For storage only: Timber floor is fine. Save the slab money for better shelving and organization inside the shed.

For a hobby workshop where precision matters: Slab is worth it. The stability makes a real difference for woodworking or any activity requiring flat, stable surfaces.

For a site with any slope at all: Timber floor unless you’re prepared to pay for proper cut-and-fill earthwork and retaining walls to create a level building pad.

Don’t cheap out on whichever option you choose. A poorly poured slab cracks and settles. Undersized or improperly spaced stumps create a bouncy floor that’s miserable to work on. Pay for proper materials and installation regardless of which foundation type you select.

The foundation is literally the foundation of your shed. Getting it right matters more than most other decisions you’ll make about the build. Spend the time and money to do it properly from the start—fixing foundation problems after the shed is built is expensive and disruptive.