On a flat block, a deck is mostly a choice of size and board. On a slope, the layout comes first. Where the ground falls away from the house, the height of the deck at its low corner, the number of levels and the way you reach the garden decide how much structure is needed, what the job costs and whether it needs approval. The boards matter less than those three things.
These are the layouts we use on sloping Illawarra and Southern Highlands blocks, and what each one involves.
A single low platform off the back door
On a gentle fall, one level just above the ground is the simplest design. It gives you flat space outside the door, a small step down to the lawn and a short subframe. This is the layout where the low end of the deck stays close to the ground, so the footings and posts stay modest.
It works best when the slope across the deck footprint is small. If the ground drops more than the deck height you are comfortable with at the far edge, the design starts to turn into a raised deck whether you planned it or not.
Stepped decks in two levels
On a steeper block, stepping the deck down in one or two levels usually beats one high platform with a tall balustrade around it. Each level follows the ground more closely, so the structure under each one is smaller, and the deck feels like part of the garden rather than something standing above it.
A stepped layout also gives you zones. The upper level, level with the internal floor, can hold the table and barbecue. The lower level can hold lounges, a spa or planter boxes. The step between them can double as seating.
The trade-off is more edge detail: more framing, more cut boards and a stair or step between levels. It tends to cost more per square metre of deck than a single flat platform, and it is usually worth it when the alternative is a very tall one.
A raised entertaining deck
Where the living room sits well above the ground, a raised deck level with the floor is often the right answer. It gives easy access from the house, and the view or aspect can be much better from up high.
Height is where the cost goes. A raised deck needs a full subframe, deeper footings, posts, wide stairs and a compliant balustrade before the first board goes down, and most of that work is underneath where you cannot see it. Our timber deck cost guide explains how height moves the price.
If a raised deck is the plan, think about the space below. Enclosing it with lattice or screening makes it look finished, and leaving it open can give you somewhere to store garden gear, provided the area stays ventilated.
Decking over an existing slab or courtyard
Not every deck needs a new subframe at ground level. Where a sound concrete slab or paved courtyard already exists, a low-profile subframe can be fixed down and the deck laid over the top. It covers tired concrete without the cost of breaking it out.
Two checks come first. The slab needs to be sound and drain properly, and the deck still needs airflow underneath. Timber decking designed for outdoor use is laid with gaps between boards so water does not pond on the surface; the WoodSolutions timber decking guide advises that spacing between boards stops water ponding on the surface, and that seasoned decking should be laid with gaps of not less than 4mm (see its decking guide).
L-shaped and wraparound decks
A deck that turns a corner can link two rooms, such as a kitchen and a living area, and give two spots with different light. On a slope, the turn is also a handy place to change level, so the L can be two stepped decks that meet at the corner instead of one long platform.
The cost is in the corner itself. Extra framing, a more complicated board layout and a longer balustrade all add up, so an L-shape is usually something to plan with the doors rather than add later.
A deck with cover
A roof over part of the deck turns it into a room that works in rain and summer sun. The structure has to be planned with the deck, because the posts and footings that carry the cover are set when the deck is built. Adding them later usually means cutting into boards that are already down.
Approval changes as well. An open deck and an open pergola can each be exempt development on their own, but a solid roof or a combined structure can step up the paperwork. Our pergolas and carports page covers the cover side, and the deck, pergola and carport approval guide covers the approval paths.
Aspect, shelter and materials
Layout is also about where the sun is. A west-facing deck can bake through summer afternoons unless there is cover, and a southern deck sits in shade through winter. On exposed blocks near the coast, a screen or partial roof can turn a deck that gets used twice a year into one that gets used weekly.
On material, hardwood suits most outdoor decks and wants an oil every so often to hold its colour. Composite needs less upkeep and is a common choice near the coast and around pools, but gets warmer underfoot in direct sun. Our merbau vs composite decking post compares them, and how often a deck needs oiling covers timber upkeep.
Height, approval and the worst corner
The deck height that matters is the height at the lowest corner, not at the back door. A deck that looks small and low from the house can sit more than a metre above the ground where the block falls away, and that can be enough to move it from exempt development to a certificate or development application.
The NSW Government explains the exempt development pathway on its Planning Portal. It notes that works must meet all of the development standards in the State Policy to be exempt, and that buildings constructed before 1990 may contain asbestos, which is worth knowing if the deck attaches to an older house.
Getting a layout priced
The best way to settle the layout is to stand on the site and look at the levels. Ovas builds timber and composite decks across Wollongong, the Illawarra and the Southern Highlands, and gives a fixed-price proposal once we have seen the block, with approvals handled before anything is built. Our decking page covers the full build, and you can send details through the contact page or call 0434 037 851.
Common questions
- What is the best deck design for a sloping block?
- It depends on the fall and where the doors are. A gentle slope often suits a single low platform off the back door. A steeper fall usually works better stepped down in one or two levels than as one tall platform with a high balustrade, because the structure underneath stays smaller and the deck sits closer to the garden.
- Can a deck be built over an existing concrete slab?
- In a lot of cases, yes. A low-profile subframe can be fixed to a sound slab and decked over, which covers tired concrete without removing it. The slab and its drainage need checking first, since the deck still needs airflow underneath to last.
- Does a deck on a slope need council approval?
- It can. A small, low deck set back from the boundaries can be exempt development, but on a slope the low corner may sit more than a metre above the ground, which changes the answer. Measure the height at the worst corner, not at the back door, before assuming anything.
Want a hand with this at your place? Get a free quote or call 0434 037 851.