Start with what you do not want to lose.
Do you value the garden, a particular outlook, the existing downstairs layout or staying on one level? Write down those priorities before comparing a second storey with a ground floor extension.
Neither option is automatically cheaper, quicker or better. The existing home, available land, proposed scope and planning pathway all need review. Ask the professionals to compare options against the same brief.
Compare the decisions side by side.
| Question | Building up | Extending out |
|---|---|---|
| Outdoor space | May preserve more garden area, depending on stairs and other works. | Uses part of the site. Consider what happens to entertaining, access and landscaping. |
| Daily movement | Introduces stairs and a relationship between two levels. | May keep more daily living on one level if the site allows it. |
| The existing structure | Requires assessment of how new loads and roof changes are managed. | Requires assessment of the new structure and connection to the existing house. |
| Disruption | Discuss roof removal, household safety and accommodation. | Discuss access, connection works and the areas affected during construction. |
| Approvals | Check the actual proposal against applicable rules. | Check the actual proposal against applicable rules. |
Price a defined option, not a slogan.
For each option, ask for the floor plan, an initial scope, key uncertainties and an explanation of what the budget includes. Compare the spaces you gain and any existing spaces you lose or need to alter.
Keep temporary accommodation, professional fees, landscaping and work to the original home in the comparison. A lower construction figure does not necessarily mean a lower total project cost.
Keep the decision open until the evidence is there.
You may decide that a smaller addition with a better layout answers the brief. You may prefer a ground floor extension or a different property altogether. A useful design conversation should help you understand those choices rather than push you towards the largest project.
Official resource: ABCB homeowner guidance on extensions and approvals.
Talk through your priorities