A frame for composite boards is a timber deck frame with the joists closer together and the tops flatter, and with a wide enough joist under every place two boards meet end to end. Get those right and the rest is ordinary carpentry. Get them wrong and no amount of careful clipping will save the deck, because composite boards follow whatever is under them. Here is the order I'd build in, with figures from Timber Queensland's data sheet on decks and from the board makers' guides. Your plans themselves come from a builder or a certifier.
Before you dig: council, height and an engineer
Height decides a lot. The ABCB Housing Provisions call for a barrier wherever it is possible to fall 1 m or more from a deck2. On a deck that barrier has to be at least 1 m high, and its openings must not let a 125 mm sphere through2. Before you dig, ask the council or a building certifier whether your deck needs approval. Timber Queensland's data sheet says a freestanding deck higher than 1800 mm should be braced in both directions between pairs of posts1.
I'd get an engineer in when the deck is high, on a slope, carrying a spa or a heavy planter, or hung off a wall that is not solid. The data sheet warns that a brick veneer wall may not be strong enough to take a ledger, and that the deck may need its own posts along the house instead1. When a member of the hardware chain's Workshop forum planned a bench of about 500 kg on a new deck extension in December 2021, the advice was to double the joists under it and stand pedestal feet on paving slabs beneath it11. That put the weight on the ground rather than on the frame, and he wrote afterwards that it felt sturdy.
Ledger or freestanding
A deck can hang off the house on a ledger or sit on its own posts. The ledger saves a row of footings, but it is a common failure point. Timber Queensland's data sheet asks for a ledger at least 90 x 45, bolted to the house framing with 12 mm hot-dip galvanised bolts or coach screws at a maximum spacing of 600 mm1. Flash over the top of it. Jack Norton of the Timber Preservers Association of Australia describes the trap: if the flashing is installed incorrectly, water gets trapped between the ledger and the wall and the timber can't dry9.
If the wall is brick veneer, or you cannot see what you are bolting to, I'd go freestanding. An extra row of posts near the house is a small job next to fixing a ledger that pulls away from the wall.
Posts and footings
Posts go on hot-dip galvanised stirrups set in concrete footings, with a 75 mm gap between the top of the concrete and the bottom of the post as a termite inspection zone1. Footings follow the building code and your soil, so don't guess them. If a post must go in the ground, it should be H5 treated pine or an in-ground durability class 1 hardwood1. Sit it on 100 mm of drainage gravel and slope the fill away from it, as the data sheet describes1. I'd avoid that where you can, because a post on a stirrup is far easier to replace than a post in concrete.
Space the posts to suit the bearer size from the span tables. Run them in straight lines so the bearers go on without packing. Set a string line and a laser before the concrete goes in, not after.
Bearers
Bearers sit on the posts, fixed with post caps or brackets or bolted into a housing, and carry the joists. Their size comes from the tables for the span between posts and the width of floor they carry. I'd pick the bearer first, then the post spacing. Posts that are too far apart give you a bearer that sags in the middle, and a sagging bearer puts a dip across the whole deck that no board can hide.
A Workshop forum member building a low deck extension in December 2023 spent more on timber so he could push his post spacing out and dig fewer holes10. Once the boards were laid he felt a spring in it barefoot that he couldn't feel in boots. His son jumped on the deck while he watched from underneath, and he could see the joists flexing mid-span. He crawled back under and added a mid-span bearer of two laminated 140 x 45 lengths on four new posts, and the spring went. He was sure the frame was well inside the code, and the long spans still showed up underfoot.
Joists: the centres, the width and the level
The joists are where a composite frame differs from a timber one. Two of the makers' guides cited here set 450 mm between joist centres for houses35, and one of them sets 400 mm for stairs, landings and commercial decks. Another caps every frame at 400 mm6. The figures are maximums. On a diagonal lay the boards span further between joists, so check the maker's guide for a closer figure before you set out. Measure centre to centre, not the gap between joists. The joist spacing guide goes deeper on centres.
Width matters at butt joins. One maker asks for 45 mm joists where top-fixed boards butt together5. Its screws can't go closer than 20 mm to a board end, so it also asks for a doubled joist or a laminated block wherever butt joins fall5. Another maker says two board ends should not share one 45 mm joist and asks for any joist under a butt joint to be double blocked4. Timber Queensland's data sheet recommends 45 or 50 mm joists where boards are nailed through the top, with 35 or 38 mm joists suitable where proprietary fixings on the side of the joist hold the boards1. One maker requires every piece of board to sit on at least three joists, which rules out short offcuts bridging one bay4. Plan where the joins fall before you fix a joist, and stagger them so there is never a seam of joins across the deck.
Joists fix on top of the bearers with skew nails or framing anchors, or in line with the bearers in joist hangers. Hangers are for a frame where the joist and bearer tops need to be flush, which saves height. Use hot-dip galvanised or stainless hardware rather than zinc-plated. Where treated pine stays damp, the data sheet asks for stainless or epoxy-coated connectors rather than galvanised ones, and near the coast or a pool it asks for more protection again1.
Then level the tops. Run a string line along the joists in both directions, and plane the high ones and pack the low ones until the string touches every joist. Composite boards are flexible and the clips pull them down tight, so a joist sitting a few millimetres proud shows as a hump in low sun for the life of the deck.
Blocking, the rim joist and the ends
Blocking is the short pieces fixed between joists. Timber Queensland's data sheet calls for solid blocking at the supports where joists are more than four times as deep as they are wide, and for rows of blocking or herringbone strutting once joists span more than 3 m: one row up to 4.2 m and two rows beyond1. One board maker's suggested framing also shows blocking, or noggins, under breaker boards and picture-frame borders4, and the border guide covers that framing. A Whirlpool member building a low composite deck settled on 400 mm centres in September 2026 after conflicting advice, and wrote that "the blocking is really bracing everything nicely together"12. He also laid his joists parallel to the fall of the old patio underneath so the water would drain between them, which is the sort of thing you can only do while the frame is still open.
The rim joist, or boundary joist, is the outer joist that runs across the ends of the others and closes the frame. It carries the fascia and the last row of boards, and on a picture-framed deck it carries the border too. Fix it to every joist end, and double it where a border mitre lands.
Leave the ends of the deck open to the air. One board maker asks for at least 40 mm of clearance where water drains freely and 90 mm where it can pool3. Another says not to seal off the deck ends with garden beds, trees or solid objects5. Replies in the same Whirlpool thread warned that a gap of a few millimetres under the joists will block with leaf litter and dirt. Fall the frame slightly away from the house so water runs off rather than into the ledger. One maker advises a fall of 1:200 away from buildings to help drainage7.
Seal the cuts, tape the tops
The next jobs are cheap and easy to skip. Preservative only works in the sapwood, so a cut end can expose timber the treatment never reached, and WoodSolutions says to reseal cut ends immediately after cutting8. Then tape the tops. One board maker suggests its self-adhesive tape over timber joists to prevent moisture damage6, and WoodSolutions recommends flashing strips or damp-proof membranes over exposed beams and joists. The joist tops take every fixing, and that is where water sits. More on the treatment itself in H3 or H4 treated pine.
What I'd do
Draw the deck first, at the joist centres for the boards you have chosen, with the butt joins marked so you know where the doubled joists go. The deck designer will do that and give you a materials list. It is a concept plan only, so take it to a builder or certifier before you order. Then build in this order:
- String lines and footings.
- Posts on stirrups.
- Bearers sized from the tables.
- Joists at the centres, with doubled ones under the joins.
- Blocking and the rim joist.
- Level the tops with a string line, seal the cuts and tape the joists.
Only then open the first pack of boards. If the site is low or wet or in a bushfire zone, read steel vs timber before you buy any pine. If you're reusing an old frame, start with composite decking on an existing deck frame. The stairs guide covers the closer stringer spacing composite treads need.