How do steel and aluminium deck frames compare?
| Steel (galvanised) | Aluminium | |
|---|---|---|
| Corrosion | Depends on the coating; Dahlsens’ Spantec is Z450 as standard | Doesn’t rust |
| Spans | Spantec lists joists spanning up to 6 m unsupported | Per maker tables: Futurewood joists span 600 to 1,800 mm |
| Build height | Spantec suits decks from 250 mm up to 6 m with its Ezipier | ClickDeck from about 30 mm; Futurewood from 48 mm |
| Fire | Ask the maker for its report | ClickDeck’s report says 6063 T6 is not deemed combustible under AS 1530.1 |
| Fixing boards | Needs steel-specific fixings | Maker’s clips; Futurewood says to cut with an aluminium blade |
The systems we’ve read aim at different heights. The aluminium ones start very low, from about 30 mm for ClickDeck, while Spantec suits decks from 250 mm up. Both need the maker’s span table, and neither replaces an engineer on a large or high deck.
How do you fix composite boards to steel?
Steel and composite expand differently, so fixings matter.
- Ekodeck pre-drills steel (3 mm for steel under 1.5 mm, 3.5 mm for 1.5 to 2.4 mm, 3.75 mm above that) and uses a 10 gauge by 40 mm countersunk metal screw.
- ModWood uses 10 gauge tek screws, 40 mm for boards up to 23 mm and 50 mm for thicker, with pre-drilling and countersinking; it doesn’t recommend nail guns.
- Futurewood says face screws through boards aren’t recommended on steel joists once boards pass 3 m, and its self-drilling screws are rated for steel up to 1.6 mm.
- NewTechWood’s Metal Fix screws suit steel joists up to 2 mm thick; it doesn’t cover Metal Fix clips on Stratco Probeam or similar double-wall profiles.
What about timber boards on steel joists?
WoodSolutions recommends against ordinary timber-deck screws. Fix a timber batten above or beside the steel joist and fasten the boards to the batten, so that expansion doesn’t shear the screws.
Is a steel frame fire safe?
In bushfire-rated zones ModWood says joists and bearers must be non-combustible or a listed bushfire-resisting timber. ClickDeck’s report covers its aluminium; for steel, ask the maker for its own. Check the board and the whole assembly against the BAL for your site.
Which should you choose?
We found one steel subframe page with published span and coating details (Spantec) and another (Steel-Deck) with no spans. Until more are verified, treat this page as a comparison of fixing methods and frame behaviour, and get the span table for any system you consider. See the aluminium frame overview for the aluminium side.
Questions
How do you build a steel deck frame?
Follow the steel system maker's span tables and brackets, then fix the boards with fixings made for steel. Dahlsens' Spantec steel subfloor, for example, uses beams from 100 by 50 to 250 by 50 mm with a Z450 coating, and lists joist spans of up to 6 m unsupported.
How do you attach wood decking to a metal frame?
Don't use ordinary timber deck screws. WoodSolutions says differential expansion can shear them, and recommends fixing a timber batten above or beside the steel joist and screwing the boards to that. Composite makers have steel-specific fixings.
Is a galvanised steel deck frame OK near the coast?
The coating decides. Dahlsens' Spantec uses a Z450 coating as standard. Ask the maker for the coating class and its coastal limits for your site.
Sources
- WoodSolutions TDG 21 Domestic Timber Deck Design (revised Oct 2020)
- Dahlsens Metal subfloor systems
- Steel-Deck / SteelMAX
- Ekodeck Designer Series Product Manual V10.25
- ModWood Fixing - Steel Joists (Oct 2018)
- CleverDeck Xtreme Fixing Guidelines
- NewTechWood Terrace Decking Installation Guide
- Fixing Instructions for ModWood Flame Shield (August 2016)
- Reaction to fire testing - Clickdeck frame (aluminium alloy 6063)
- ClickDeck flyer
- ClickDeck - aluminium decking subframe (home page)