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What is the difference between joists and bearers on a deck?
Joists carry the boards and sit across the bearers. Bearers carry the joists and sit on the posts. Timber and aluminium frames use the same layout. Our joists and bearers guide explains how the pieces connect, and the AS 1684 tables that size timber ones.
What aluminium joists are available?
| System | Joist size | Length |
|---|---|---|
| Futurewood CleverDeck | 25, 50 or 90 mm high by 45 mm wide | 5,400 mm |
| NewTechWood StructurAL | 60 mm wide by 40 mm high | 3,000 mm |
| ClickDeck | profiles 28, 55, 110, 150 and 200 mm | 28 mm in 3.6, 4.8 or 6 m; 55 mm in 2.4, 3.6, 4.8 or 6 m; 110 mm in 3.6, 4.8 or 6 m; 150 and 200 mm in 6 m |
Deeper profiles span further. Within Futurewood’s range, the 25 mm joist is tabulated at 500 mm and the 90 mm joist at 1,800 mm for a residential single span.
What spacing do aluminium joists need?
Two limits apply, and they come from different documents. The board maker sets the centre-to-centre spacing: 450 mm for most Australian composite boards, and 450 mm in Futurewood’s own tables. The frame maker sets how far each joist can span between pedestals or posts. Futurewood also notes that a closer spacing is stronger: 400 mm beats 450, and 300 beats 400. For diagonal boards, Futurewood’s board spacing drops to 350 mm at 45 degrees and 250 mm at 30.
NewTechWood’s StructurAL limits the gap between pedestals under the joists to 75 cm with a 20 cm overhang, and sets joist spacing by the board maker’s recommendation.
How do aluminium joists compare with timber ones?
Timber joists follow the AS 1684 tables. WoodSolutions recommends joists at least 45 mm wide in seasoned hardwood or treated softwood, and its Table 2 limits spacing for timber boards to 400 to 500 mm. Aluminium joists follow the maker’s table and only with the maker’s parts. Futurewood says its tables apply only with its own boards, brackets, clips and pedestals.
For the numbers and their conditions, see the span tables guide.
Questions
What are aluminium decking joists?
Extruded aluminium sections that do the job of timber joists: they span between supports and carry the boards. Futurewood's are 25, 50 or 90 mm high and 45 mm wide, and NewTechWood sells a 60 by 40 mm joist in 3 m lengths.
Can aluminium joists be used for composite decking?
Yes, where the board maker approves the system. Check the joist centres the board allows and the span table for the joist. Our compatibility guide lists what makers say.
Where can I buy aluminium joists in Australia?
From the system makers and their stockists. Bretts lists NewTechWood's 40 by 60 mm by 3.0 m joist as a special-order item, and Dahlsens stocks ClickDeck.
Sources
- WoodSolutions TDG 21 Domestic Timber Deck Design (revised Oct 2020)
- Futurewood CleverDeck Aluminium Deck Frame System Installation Guidelines, Appendix 1 Span Tables (V1, June 2024)
- Futurewood Aluminium Subframe
- NewTechWood NIVO Pedestals Technical Information and Span Tables
- NewTechWood StructurAL Installation Guide 2021 AUS
- Bretts NewTechWood Aluminium Joist
- CleverDeck Xtreme Fixing Guidelines
- Clickdeck Span Table (ref ALU261223)