A sloping block is where a deck earns its keep. The ground falls away from the back door, the yard is hard to use, and a deck turns that slope into a flat outdoor floor at the same level as the house. It also brings in more rules than a deck on flat ground, because the higher end can be well above the ground below.
Measure at the low side
The height that counts is from the deck floor down to the ground at its lowest point, not at the back door. On a sloping block a deck can be 300 mm off the ground at the house and 2 m off it at the far edge. Measure both ends before you start planning, because the low side decides the balustrade, the stairs and the approval.
Approval is almost certain
Under the Building Regulation 2021, a deck is exempt from building approval only while it has no roof, is no more than 10 m² and its floor is no more than 1 m above the ground. Most decks on a slope pass the 1 m mark somewhere, so they need a building approval from a certifier, with engineering. We include that in the job.
Balustrades
Once someone could fall 1 m or more from the deck, it needs a balustrade at least 1 m high above the floor, with no gap that a 125 mm sphere can pass through. Where the floor is more than 4 m above the ground, the balustrade must not have footholds that a child could climb between 150 mm and 760 mm above the floor. On a slope, the balustrade usually runs along the low side and returns down the sides. Our deck approval guide covers this in more detail.
Stairs
Stairs off a raised deck have their own rules, which your certifier checks against the National Construction Code. The main ones are:
- Risers (the height of each step) between 115 mm and 190 mm, and goings (the depth of each tread) between 240 mm and 355 mm, kept the same all the way up a flight.
- A handrail on at least one side once the stair rises more than about 1 m, at least 865 mm above the line of the treads.
- Openings between treads small enough that a 125 mm sphere cannot pass through, once the stair is high enough to need a balustrade.
- A landing to break a long flight. A flight can have no more than 18 risers.
Stairs take up more room than people expect. A deck 2 m above the ground needs around eleven risers and a run of about 2.5 m to 3 m, plus a landing at the bottom. We draw the stairs as part of the deck so they land somewhere useful.
Footings on a slope
- Posts on the low side are taller, so they carry more bracing and often bigger footings.
- Footings go into firm natural ground, not into fill or the loose soil at the edge of a cut.
- Footings near a retaining wall must stay out of its zone of influence, or the wall and the deck are designed together.
- On reactive clay, footings go deep enough to get below the soil that moves with the seasons.
Steep land in Logan
Logan’s planning scheme sets extra rules on steep ground. Where council mapping shows a slope of 12% or more, or a historical landslide area, building work needs a site-specific geotechnical report certified by an engineer, and cut and fill is limited. A lot that cannot meet those rules becomes an application to council, with a council fee of $869 in the 2026-27 register. We check the landslide overlay for your lot at the quote, and our sister site can show you the overlays on your lot before then.
Using the space underneath
A deck that sits 2 m or more above the ground leaves a lot of room under it. Steel framing with longer spans means fewer posts, which makes that space more useful for storage or a shaded sitting area. Plan for drainage before it goes in: water from the deck and the slope above has to run somewhere other than under your new storage area.
Privacy
A raised deck looks over fences. On the Gold Coast, where a raised deck has a direct view into the private open space of the neighbour’s home, the City asks for a privacy screen with at least 50% transparency. Elsewhere it is often about your own comfort, but we look at the neighbours’ windows and yards before we fix the deck height.
A roof over it
A roofed deck is never exempt from approval, whatever its height. If you want a roof now or later, the posts and footings need to carry it, so design for it on day one. On a two-storey home, a flyover roof lets light into the house and lifts the roof clear of the gutter.
