Choosing the Right Foundation System for Your Residential Project

Common Types of Foundations for Houses

Residential foundations generally fall into two major categories:

• Shallow Foundations – built near the ground surface and transferring loads to shallow soil layers.
• Deep Foundations – extending deeper into the ground to reach stable soil or rock.

Both types can be used successfully, depending on your site's conditions, building type, and budget.

Shallow Foundations

Shallow foundations are typically used when strong, stable soils exist within the upper few metres of the ground. They are generally simpler, faster, and more cost-effective to construct than deep foundations.

Typical shallow foundations include:

• Stump Foundations (Subfloor Systems)
• Stiffened Raft Slabs
• Waffle Pod Slabs
• Isolated Pad Footings

These systems are ideal for single and double-storey residential dwellings on relatively flat sites with moderate soil reactivity.

How to Choose the Right Foundation System

There is no one-size-fits-all solution when it comes to house foundations.
The best system depends on a combination of:

• Soil conditions (strength, reactivity, depth to rock)
• Slope of the site (flat vs steep)
• House size and construction type (lightweight vs heavyweight materials)
• Design life and performance expectations
• Construction budget and site constraints
• Local contractor capabilities and preferences

Your Structural Engineer will assess these factors carefully, often with input from a Geotechnical Report, before recommending the right option.

Overview of Residential Foundation Types

Now, let’s explore the most common foundation options used in Australian residential projects in more detail:

Stump (Subfloor) Foundations

Stump foundations elevate your house above the ground surface using regularly spaced supports called stumps, which sit on concrete pads.

This traditional method is common for lightweight timber-framed homes, especially in areas prone to flooding, high moisture, or on sloping sites.

Advantages:

• Ideal for sloping blocks where excavation would be costly.
• Allows for good ventilation beneath the home, helping manage moisture and termites.
• Easier future access to plumbing, wiring, and services running underneath the floor.
• Faster construction time for small houses.

Disadvantages:

• May be prone to settlement, especially on reactive clay soils without proper engineering.
• Timber stumps (if used) are vulnerable to termite attack and decay unless properly treated.
• Requires careful maintenance and inspections over time.

When to use:

• Lightweight houses (timber or lightweight steel frame).
• Sloping blocks or flood-prone areas.
• Sites with moderate ground conditions.

Stiffened Raft Slab

A stiffened raft slab is a thick, reinforced concrete slab integrated with beams ("ground beams") cast in-situ to form a strong, continuous foundation system.

The beams distribute loads evenly, helping to resist cracking and movement due to soil expansion and contraction—especially important in reactive soils classified as Class M, H, or E in AS 2870.

Advantages:

• Provides excellent stability even on moderately reactive soils.
• Suits both lightweight and heavier brick-veneer construction.
• Creates a solid "feel" underfoot for occupants.
• Minimises differential movement between walls and floors.

Disadvantages:

• More concrete and excavation required than waffle slabs.
• Harder to retrofit plumbing or electrical conduits after construction.

When to use:

• Moderate to highly reactive clay sites.
• Traditional single or double-storey homes with masonry cladding.
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Waffle Pod Slab

Waffle slabs are a cost-effective, lightweight alternative to raft slabs, using polystyrene pods to form the voids and ribs within the slab.

Waffle pods reduce the amount of excavation and concrete used, making this a popular choice for residential developers aiming for efficient builds on flatter, stable sites.

Advantages:

• Very fast construction.
• Lower concrete usage reduces material costs and environmental impact.
• Good thermal insulation properties (air pockets under slab).

Disadvantages:

• Highly sensitive to poor site preparation (compaction, drainage).
• Not recommended for sloping sites or highly reactive soils without specific engineering adjustments.
• Environmental concerns due to polystyrene waste during construction.

When to use:

• Flat, well-drained sites with low to moderate soil reactivity.
• Projects with strict budget or time constraints.

Isolated Pad Footings

Isolated pad footings are individual concrete pads supporting concentrated loads—such as steel or timber columns—rather than continuous wall loads.

Typically combined with suspended timber floors or steel framing systems, they allow loads to be transferred directly into deeper soil layers.

Advantages:

• Economical where concentrated loads are present.
• Easier to design and build for smaller or open-plan structures.
• Reduces material use compared to full slabs in the right application.

Disadvantages:

• Poorer performance where uniform load distribution is needed.
• Vulnerable to differential settlement without careful geotechnical design.

When to use:

• Architecturally designed homes with minimal wall loads and heavy point loads.
• Rural projects where simpler construction is preferred.

Deep Foundations

Deep foundations are required where surface soils are weak, highly reactive, or unsuitable for bearing loads.
In these cases, foundations are extended deeper to reach more competent materials, such as hard clays, dense sands, or rock.

Common deep foundations include:

• Screw Piles
• Driven Piles
• Bored Piles
• Basement Foundations

Deep foundations are more expensive but essential for ensuring stability on poor soils or heavily loaded structures.

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Screw Piles

Screw piles involve helical steel shafts mechanically driven into the ground until they achieve the specified load capacity.

They are an efficient solution when surface soils are poor but strong layers exist at moderate depths.

Advantages:

• Fast installation without vibration or spoil generation.
• Minimal impact on neighbouring properties.
• Suitable for restricted or difficult-access sites.

Disadvantages:

• Limited to moderate load capacity applications.
• May not penetrate very dense or rocky layers.

When to use:

• Lightweight to medium-weight homes on soft clays or fill.
• Sites with shallow water tables or limited access.

Driven Piles

Driven piles are hammered into the soil by large machinery, displacing the soil around them rather than removing it.

This type of piling is robust and commonly used where deep sandy or loose soils exist.

Advantages:

• Rapid installation for large projects.
• Piles gain additional load capacity through friction with displaced soil.
• Minimal spoil generated.

Disadvantages:

• High noise and vibration during installation.
• Specialised equipment required.

When to use:

• Coastal or sandy sites.
• Heavier, multi-storey homes.

Bored Piles

Bored piles involve drilling a hole, placing reinforcement cages, and concreting in place.

They offer the highest load capacity and are preferred where deep, high-strength foundations are necessary.

Advantages:

• Suitable for most soil types, including sites with shallow rock.
• Extremely strong and durable.
• Minimal vibration during installation.

Disadvantages:

• High construction cost.
• Large volumes of spoil generated.
• Longer construction timelines compared to screw or driven piles.

When to use:

• Challenging soil sites requiring high load resistance.
• Large or architecturally complex homes.

Comparing Foundation Options at a Glance

Still unsure which foundation system is right for your home?

The table below provides a side-by-side comparison of the most common residential foundation types used in Australia.
It compares each option based on key factors like cost, movement resistance, suitability for reactive soils, construction speed, and typical use cases.

This is a helpful tool for homeowners, builders, and designers looking to quickly understand the pros and cons of each system—and have more informed conversations with their Structural Engineer or builder.

💡 Tip: Use this table alongside your site’s soil classification and project requirements to narrow down the most suitable foundation types. If you’re unsure, we can help validate the best option using AS 2870:2011 and your geotechnical report.

Want To Take It a Step Further & Quickly Estimate Your Foundation Requirements?

We’ve created two free online calculators to help you get started with early-stage planning:

• Imposed Bearing Pressure Calculator
  Enter your structure’s total weight and base area to estimate the imposed pressure on the soil. Ideal for comparing against your site’s allowable bearing pressure from a geotechnical report.
• Minimum Base Area Calculator
  Enter your structure’s weight and the allowable bearing pressure of your site, and it will calculate the minimum required footing area to safely support your load.

👉 Try the Foundation Calculators here

These tools are designed to give you an initial sense check before engaging your engineer.

‍(For full compliance and design, always confirm with a qualified Structural Engineer using AS 2870:2011 and site-specific geotechnical data.)

Final Thoughts

Choosing the right foundation system isn’t just about cost—it's about protecting your home's value and performance for decades to come.
By understanding your options, you can have more informed conversations with your engineer and builder.

At Brushwood Engineering, we help homeowners and developers design safe, efficient, and compliant foundations that stand the test of time.

Contact us today to discuss your project and get expert advice tailored to your site.