Choosing between a ground-floor extension ($2,200 to $3,800 per square metre) and a knockdown-rebuild ($1,900 to $3,200 per square metre) depends on your existing home's structural integrity, site slope, and heritage overlays. While rebuilding yields a lower rate per square metre across large footprints, extensions preserve existing capital and reduce rental holding costs.

Removing a residential load-bearing wall costs between $3,500 and $11,000 including structural engineering sign-off, temporary shoring, and steel beam installation. Because the wall supports roof or upper-floor loads, an engineer must calculate the span and specify either an engineered laminated veneer lumber (LVL) beam or a structural steel universal beam (RSJ).

A second-storey addition typically costs between $2,800 and $4,500 per square metre depending on structural reinforcement, roof redesign, and plumbing fixtures. Before building upward, a licensed structural engineer must evaluate existing foundation footings, soil bearing capacity, and ground-floor load-bearing walls to verify whether underpinning or steel point-load columns are required.