If you have backyard to spare and want new living space that opens to the garden, a ground-floor extension is usually the simpler and cheaper option per square metre. If the block is tight, or building out would swallow the yard, a second-storey extension keeps your outdoor space, but it costs more per square metre and needs an engineer to confirm the existing house can carry it. The right answer depends on your block, the structure you already have and how you want to live.
Side by side
| Ground-floor extension | Second-storey extension | |
|---|---|---|
| Published cost (Adelaide) | $2,800 to $4,500 per m² for a single-storey rear extension (Templeton Built, Jul 2025) | $3,500 to $5,500 per m² (Templeton Built, Jul 2025) |
| Backyard | Uses yard space | Keeps the yard |
| Structure | New footings, slab and roof, tied into the house | Existing footings and walls checked by an engineer; may need strengthening |
| Staircase | Not needed | Needed, and it takes floor space downstairs |
| Living at home during works | Usually possible | Harder while the roof is open |
| Planning issues to design for | Setbacks and site coverage | Height, overlooking and overshadowing |
When building out makes sense
A ground-floor extension suits the bigger allotments common in established suburbs like Elizabeth and Munno Para, where many homes have good bones, a closed-in layout and a deep backyard. Extending at the back lets you open the kitchen and living areas straight onto an alfresco and lawn, which is what most families are after.
It is also the better fit when you want to stay in the house during the build, when anyone in the household finds stairs difficult, or when you are adding a wet area that is easier to plumb at ground level. Keep in mind that the Planning and Design Code sets zone rules for things like setbacks and how much of the block can be built on, so the size of a ground-floor extension has limits too.
When going up makes sense
A second-storey extension makes sense on smaller lots, which are common in newer estates like Riverlea Park and the newer releases around Angle Vale, where there is little yard to give up. It is also a good way to separate the household: a parents' retreat upstairs, or kids' bedrooms and a rumpus away from the main living area. One of our own Riverlea Park builds includes an upstairs retreat for exactly that reason.
Budget Direct notes a second storey can cost up to 50% more than building out, depending on how much structural reinforcement the house needs (Budget Direct, July 2026). That premium buys you space without losing the garden.
What going up actually involves
- An engineering check first. The existing footings and walls were designed for a single storey. Much of northern Adelaide is on reactive clay, so the engineer looks closely at the footings and the soil before anything is designed.
- A staircase. It needs a spot downstairs, usually taking space from a bedroom, hallway or living area, so plan its position early.
- The roof comes off. Part or all of the roof is removed and the house is weather-protected while the new floor and frame go on.
- Services. An upstairs bathroom or ensuite needs plumbing routed through the existing house, and the electrical work grows too. Ours is done in-house by ASP Electrical Installations.
- Privacy design. Planning assessment considers overlooking and overshadowing, so upstairs windows and balconies facing neighbours may need screening or higher sills.
The in-between option
Sometimes the best answer is both: extend at ground level and build a new upper room over the extension rather than over the old house. The new structure is designed from scratch to carry the second floor, which can be simpler than strengthening the original house.
Questions to answer before you choose
- How much yard do you really use, and how much do you need to keep?
- Can you live elsewhere for part of the build if the roof has to come off?
- Where would a staircase go without wrecking the downstairs layout?
- What do your zone rules allow on height, setbacks and site coverage? Check your address on PlanSA.
- Is the house worth this investment at all, or is a rebuild the smarter path? See our guide to knock down rebuild vs renovating.
We design and build both ground-floor additions and second-storey extensions, with the engineering, structure and staircase managed as one project. See our home extensions service, or read what drives the cost of an extension first.
Common questions
Is a second-storey extension cheaper than building out?
Usually not per square metre. Templeton Built publishes $3,500 to $5,500 per square metre for second-storey additions in Adelaide, against $2,800 to $4,500 for single-storey rear extensions (July 2025), and Budget Direct says a second storey can cost up to 50% more. Going up can still be the better value if it saves your yard.
Can any house take a second storey?
Not without checking. The existing footings and walls were designed for one storey, so a structural engineer needs to assess them, and the soil, before design starts. Some houses need strengthening; in others it is simpler to build the upper level over a new ground-floor extension.
Will I need to move out during a second-storey extension?
You may need to for part of the job, particularly while the roof is off. With a ground-floor extension most families can stay at home, with the opening into the existing house done late in the build.
Do you build second-storey extensions in Adelaide?
Yes. ASP Build & Co designs and builds second-storey extensions as well as ground-floor additions, with the engineering, structure and staircase integration managed as one project.
Related pages
Sources
- Templeton Built, 2025 renovation cost guide: kitchen extension ideas (21 July 2025)
- Budget Direct, How Much Do House Extensions Cost in Australia? (updated 29 July 2026)
- PlanSA, Types of consent
- PlanSA, Zoning for a property
Rules and published figures checked on 5 October 2026. Third-party cost ranges are not ASP Build & Co prices; we quote every job individually after a site visit.
