The maximum footprint of your home depends on the total size of your section and WDC’s rules around site coverage (the percentage of the land that can legally be covered by buildings).

In Whanganui the standard maximum site coverage is 40%.

For example, if you are building on a 400sqm section, all permanent roofed structures combined (including the house, any standalone garages, carports, or garden sheds) cannot cover more than 160sqm of the ground.