Granny flats have become one of the most popular ways for Brisbane homeowners to add rental income or space for family — without the cost of a full house move or a two-storey extension. But most of the planning conversation happens around floorplans, council approval, and finishes. The groundwork that has to happen before any of that gets built is usually the last thing anyone thinks about.
That’s a problem, because on a lot of South-West Brisbane blocks, the groundwork is what determines whether the granny flat can go where you want it at all.
Where a Granny Flat Actually Gets Built
Secondary dwellings almost always go in the back yard — which sounds simple until you consider how that space actually gets used. It’s usually the part of the block furthest from the street, reached only through a side gate or a narrow gap beside the house. It’s also often the part of the block that’s never had machinery on it before, which means the ground hasn’t been tested, graded, or drained with a structure in mind.
Before a slab or footings go in, that ground typically needs:
– Levelling and grading — most back yards have some slope, and a granny flat needs a properly prepared, level pad
– Footing or slab excavation — to the depth and spec required by the granny flat’s engineering, not just a scrape of topsoil
– Drainage work — stormwater has to go somewhere once there’s a new roof and a new hard surface where lawn used to absorb it
– Services trenching — power, water, and sometimes sewer need to run from the main house to the new dwelling
The Access Problem, Again
All of that groundwork needs machinery, and the back yard is exactly where access is tightest. A side gate of 700-800mm is common across the older suburbs — Moorooka, Salisbury, Sunnybank, Rocklea and nearby — and a standard excavator simply won’t fit through it.
This is where granny flat projects stall in a very specific, avoidable way: the dwelling gets designed, drawn, and approved, and then the builder discovers on-site that there’s no way to get earthmoving equipment to where the slab needs to go. At that point, the options are all worse than if it had been checked earlier — a smaller machine gets sourced at a premium, hand excavation gets used for what should be machine work, or the gate and a section of fence come out to make room.
What to Check Before You Finalise a Design
– Measure the narrowest access point between the street or driveway and where the granny flat will sit
– Confirm what width machinery your builder is assuming in their groundwork quote
– Ask about drainage specifically — a new dwelling changes how water moves across the block, and that needs to be planned, not discovered after the first heavy rain
– Get the services trenching route confirmed, since it often runs through the same tight access as the excavation
720mm-wide rubber-tracked micro-excavators are built for exactly this situation — narrow enough for a standard side gate, capable enough to handle pad preparation, footing excavation, drainage, and trenching without the yard needing to be torn up to get a machine in.
Getting It Right the First Time
A granny flat is meant to be a straightforward way to add value and income to a property. It stays straightforward when the groundwork is checked and planned before the design is locked in — not discovered as a surprise once the builder’s already on site.
Planning a granny flat or secondary dwelling in South-West Brisbane?
GateDig connects Moorooka and South-West Brisbane properties with a vetted restricted-access excavation contractor — for pad preparation, footings, drainage, and trenching on blocks where a side gate is the first thing to plan around.