Underpinning for Second Storey Adelaide

Adding a second storey to your Adelaide home is one of the most effective ways to increase living space without sacrificing your garden or dealing with land subdivision. But there’s a critical question that determines whether the project will succeed long-term: can your existing foundation handle double the load?

For most Adelaide homes built before the 1990s, the answer is no — not without underpinning. Through ADL Underpinning, you can connect with licensed contractors who prepare existing foundations for second storey additions so your builder can proceed with confidence and your new upper level won’t cause the house to crack and settle.

Why Second Storey Additions Need Underpinning

Your home’s original foundation was designed for a single-storey building. When you add a second storey, you’re roughly doubling the weight that the foundation must carry — walls, roof, floor structure, and live loads. On Adelaide’s reactive clay soils, this increased load accelerates settlement and can trigger significant cracking.

The specific problems include:

• Increased bearing pressure — shallow footings that were adequate for one storey may now push the soil beyond its capacity, causing it to compress and settle
• Concentrated loads — new load-bearing walls, steel beams, and columns for the upper level create point loads that the existing footings weren’t designed for
• Soil reactivity — the additional load drives the foundation deeper into Adelaide’s reactive clay zone, increasing vulnerability to seasonal shrink-swell cycles
• Existing movement — if the foundation was already showing signs of stress (cracking, unevenness), additional load will accelerate the problem dramatically

How We Prepare Your Foundation for a Second Storey

1. Foundation assessment — before plans are finalised, we inspect the existing foundation: type, depth, condition, and current performance. We identify any existing movement and assess the soil profile
2. Engineer coordination — we work with your project’s structural engineer to design underpinning that matches the new load requirements. The engineer calculates the additional loads from the second storey and specifies what the existing foundation needs to safely carry them
3. Underpinning design — based on the engineering analysis, we develop an underpinning plan: method, pile/pier locations, depths, and capacities. This is integrated with the second storey structural design so everything works as a unified system
4. Pre-construction underpinning — we complete the foundation upgrade before the builder starts the second storey. This ensures the foundation is certified and ready to receive the new loads
5. Certification — the structural engineer certifies the underpinning, providing documentation for the building certifier and ensuring compliance with the Building Code

Best Methods for Second Storey Underpinning

Screw Piles

Screw piles are often the best choice because they provide high capacity, immediate load bearing, and can be positioned precisely at new load points (under steel columns, new wall lines, beam supports). Installation is fast — typically 2–4 days for a standard home.

Beam and Base

Beam and base underpinning provides the highest capacity and best load distribution. The reinforced concrete beam system ties the new underpinning pads together, creating a rigid foundation that handles the increased loads and prevents differential movement. This is the go-to method for heavily loaded second storey additions.

Micropiles

Micropiles are used when ground conditions are variable (rock, fill, obstructions) or when piles need to be installed through the existing slab. Their high capacity-to-diameter ratio makes them effective even in tight spaces.

What Your Builder and Engineer Need to Know

If you’re working with an architect or builder on a second storey addition, here’s what we’d recommend:

• Get the foundation assessed early — during design stage, not after plans are finalised. This allows the engineer to design the second storey structure and the underpinning as an integrated system
• Budget for underpinning from the start — it’s not an unexpected extra; it’s a standard requirement for most Adelaide second storey projects
• Sequence the work correctly — underpinning first, then second storey construction. Never the other way around
• Consider the whole building — even if only part of the house is going up, the entire perimeter may need underpinning if the existing footings are inadequate

Second Storey Underpinning Costs

Foundation upgrades for second storey additions typically cost:

• Partial upgrade (localised reinforcement at key load points): $15,000–$30,000
• Full perimeter underpinning (standard residential): $30,000–$55,000
• Comprehensive upgrade with beam and base (large or complex homes): $55,000–$90,000+

This is typically 5–10% of the total second storey addition cost. Compare that to the cost of remediation if the foundation fails after the second storey is built — which could include demolishing and rebuilding parts of the upper level.

For a project-specific estimate, request a free quote.

Planning a Second Storey? Start Here

Email us at chris@adlunderpinning.com with a brief description of your project and any photos of existing cracking or damage. We’ll assess the foundation and provide a clear recommendation — including an indicative budget — so you can factor it into your second storey planning from the beginning.