Going up instead of out is one of the most appealing ways to add space — you keep your backyard, your land, and usually your address. But before the architectural drawings start, there's a question that decides everything: can the house you already own carry another level?
Here's what a structural engineer actually assesses, what happens when the answer is "not as it stands," and the order of steps that saves people the most money.
Most homes can support a second storey — with the right engineering. The real question is rarely "is it possible?" but "what will it cost to make it capable?"
That's why the structural assessment should be one of the first things you commission, not something you get to after paying for a full set of architectural plans. It's the single piece of information that determines both feasibility and budget.
The starting point, and usually the deciding factor.
The engineer assesses depth, condition and bearing capacity, not just type.
What's holding the roof up now has to hold considerably more.
A detail most homeowners don't know: trussed roofs are engineered specifically not to carry load from above. Cut-and-fit construction (rafters and ceiling joists) generally offers more flexibility.
In most second-storey projects the existing roof comes off entirely anyway — but the existing structure still tells the engineer a lot about how the house was designed and how loads currently travel.
Your site classification drives how much additional footing work is required:
(See our guide to [site classification] for what these classes mean.)
This is the part that ties it together. Every new load from the upper floor has to travel continuously down through walls, into footings, and safely into the ground. An engineer traces that whole path — including where a previous renovation may have interrupted it.
"Not as it stands" rarely means "no." It usually means choosing between these:
Underpinning. Extending or deepening existing footings to carry the extra load. Effective, but the most expensive option — commonly $15,000–$50,000 depending on soil, depth and access.
Supplementary footings or piers. New footings installed at key load points rather than underpinning the entire perimeter.
Steel posts and beams. Transferring upper-floor loads down through a new steel frame to new footings — often used with brick veneer homes, commonly around $8,000–$20,000.
Lightweight construction. Building the upper level in timber or light gauge steel (LGS) rather than heavier materials. This reduces the dead load reaching your existing footings — which can reduce, and sometimes avoid, underpinning altogether. It also tends to build faster.
A partial second storey. Placing the addition over the structurally strongest portion of the house rather than the full footprint.
If your footings are marginal, the material you build the upper level from stops being an aesthetic decision and becomes a budget one.
A lighter upper floor means less load into the existing structure, which can mean less strengthening work below. On homes with older strip footings, that difference sometimes decides whether a project stacks up financially. It's worth asking your engineer to compare options before the design is locked in — not after.
Two separate budgets people often confuse: the engineering and the build.
| Item | Indicative 2026 range |
|---|---|
| Structural feasibility assessment | $800 – $3,500 |
| Full structural engineering design (two-storey) | $2,000 – $8,000+ |
| Underpinning, if required | $15,000 – $50,000 |
| Steel strengthening (posts, beams) | $8,000 – $20,000 |
| Build cost (builder's scope, not engineering) | Sydney: roughly $2,800 – $5,000 per m² |
The feasibility assessment is the cheapest insurance available on a project of this size. Spending it early can save you from spending far more on a design that was never viable.
This is where most budget blowouts start. The sequence that works:
The expensive mistake is reversing steps 1 and 2 — commissioning full architectural drawings, then discovering the footings can't carry the design and paying to redraw it.
Pathways differ by state:
Allow roughly 4–6 weeks for design and documentation before approvals begin.
Not deal-breakers — just flags worth mentioning to your engineer early:
QED Engineers assesses existing structures and designs second-storey additions across [QLD, NSW, VIC & ACT] — including light gauge steel (LGS) solutions where reducing load on existing footings makes a project more viable.
Send us your plans and property details for a fast fee proposal.
Request a Free Quote | Call: 0421 157 963
Costs in this article are indicative 2026 estimates for budgeting purposes only. Whether your home can support a second storey — and what strengthening it needs — must be determined by a qualified structural engineer assessing your specific property.
Can any house have a second storey added? Most can, with appropriate engineering. What varies enormously is the cost of getting the existing structure ready. Homes with slab foundations, double brick or timber framing are often straightforward; older homes on shallow strip footings, or single-skin masonry, typically need more work.
Do I need underpinning for a second storey? Not always. It's required when existing footings can't carry the additional load, and is more common in pre-1980s homes with strip footings. Lightweight upper-floor construction can sometimes reduce or avoid the need for it.
How much does a structural assessment cost? Typically $800–$3,500 depending on the size and complexity of the home and how much investigation is needed. Full engineering design for the addition is a separate, larger cost.
Should I see an engineer or an architect first? Speak to a structural engineer early — ideally before finalising an architectural design. Knowing what your structure can carry shapes the design and prevents paying to redraw plans that aren't viable.
Does the whole roof have to come off? In most full second-storey additions, yes. Builders install temporary weather protection during that stage, which is worth planning around if you intend to stay in the home.
Is a second storey cheaper than extending out? Not necessarily. Going up avoids losing land and often avoids new ground-floor footings, but adds structural strengthening, roof removal and access costs. The comparison depends heavily on your existing structure and site.
