Imagine your home extension plans have already been approved and the excitement is building, only for your builder to tell you the existing footings won't hold the second storey you designed. Maybe what you have in mind is a new living space out the back, a second bedroom for a growing family, or a kitchen that finally opens onto the yard; plans like these usually take shape long before a single wall goes up.
One part of the process rarely gets the same attention as the design itself, yet it is the part that decides whether those plans are actually achievable as drawn. Your foundation should shape the design from day one, rather than being bolted on once the layout is already locked in. Skipping this step is one of the most common reasons homeowners end up back at the drawing board weeks or months after they thought the hard decisions were behind them.
Every extension, no matter how modest or ambitious, depends on what is happening beneath the ground. Soil in and around Melbourne's eastern suburbs varies significantly from one street to the next, and sometimes from one side of a block to the other.
Falling for a floor plan before checking what your footings can actually support usually means a costly redesign partway through the process, and that is a position most homeowners would rather avoid altogether.
A soil report, sometimes called a geotechnical report, differs from the standard building inspection most homeowners already know. Rather than assessing the existing structure, it examines the soil classification for your site, how that soil behaves as moisture levels change through the year, and how much load the ground can safely bear.
This directly shapes how footings are engineered for your extension. Completed early ideally before concept designs are finalised it gives your builder and designer the details they need to draw plans that are realistic from the outset. (For background on how reactive soils affect footings, CSIRO's Foundation Maintenance and Footing Performance guide is a widely used homeowner reference.)
In most cases, a soil test is strongly recommended before you finalise your home extension plans, particularly if your property sits on reactive clay or your home was built more than a couple of decades ago. It identifies how the ground will behave over time and what kind of footing design your extension actually needs to remain stable.
Skipping this step does not remove the risk, it simply delays when that risk becomes visible, and that often happens at a stage where changes are far more disruptive and costly to make.
Most surprises come down to a handful of recurring issues that a proper assessment tends to uncover well before construction begins. Reactive clay causes noticeable ground movement between wet and dry seasons, and footings that were not designed with that movement in mind can crack or shift over time. Existing footings on older homes are frequently undersized for the original build, let alone for the added weight of a second storey or a substantial rear extension. Poor drainage around the extension zone can also undermine footing stability gradually over the years, and this is exactly the kind of issue a proper site assessment catches early rather than one your builder discovers halfway through the build.
Once you understand the ground you are building on, decisions about storeys, position and materials become a lot clearer.
With extensive years of trading history across Melbourne's eastern suburbs, Craft Built Homes has seen firsthand how often foundation conditions get overlooked until they cause a problem.
Foundation assessment is part of our earliest conversations about your extension not something addressed once the design is already finalised. Your plans are built around what your property can genuinely support from day one. See our full build process.
