COLORBOND® or ZINCALUME® steel for a shed near the Queensland coast?
Australian conditions · Updated · 6 min read · BWG Sheds
Short answer
It depends on how close the shed is to breaking surf or salt water, and walls need more distance than roofs. BlueScope's guides recommend ZINCALUME steel and standard COLORBOND steel roofing more than 200 m from breaking surf, COLORBOND Ultra steel from 100 m, and SUPERDURA Stainless closer. For walls, which rain washes less, the distances rise to over 1,000 m for ZINCALUME and over 800 m for standard COLORBOND steel.
- Roofing: ZINCALUME and standard COLORBOND steel more than 200 m from breaking surf; COLORBOND Ultra more than 100 m.
- Walling needs more distance: ZINCALUME more than 1,000 m, COLORBOND Classic or Matt more than 800 m from surf.
- BlueScope names Queensland examples: Gold Coast and Sunshine Coast beaches are surf; Moreton Bay and Hervey Bay are exposed.
- Fasteners: Class 3 minimum; Class 4 from 200 m to 1 km from marine influence.
- Stainless steel screws are incompatible with COLORBOND and ZINCALUME steel.
What the two products are
Both are BlueScope products. ZINCALUME steel is steel strip with an aluminium, zinc and magnesium alloy coating. COLORBOND steel uses an alloy-coated substrate with factory-applied paint systems in Classic, Matt or Metallic finishes. For harsher environments BlueScope makes COLORBOND Ultra steel, and for very severe environments SUPERDURA Stainless. The choice is less about colour and more about how much salt the building will see.
BlueScope's distance guidance
BlueScope's selection guides give minimum distances from the marine source, measured from the high-water mark. They are a guide only, and they differ for roofs and walls because roofs are washed by rain and walls much less so.
| Product | Roofing | Walling |
|---|---|---|
| ZINCALUME steel | More than 200 m | More than 1,000 m |
| COLORBOND steel (Classic, Matt) | More than 200 m | More than 800 m |
| COLORBOND Metallic steel | More than 200 m | More than 1,000 m |
| COLORBOND Ultra steel | More than 100 m | More than 500 m |
| SUPERDURA Stainless | Any distance | Any distance |
For calm marine environments such as protected bays, harbours and canal estates, the distances are shorter; BlueScope's walling guide, for example, gives more than 200 m for standard COLORBOND steel in calm marine conditions. BlueScope's walling recommendations assume a six-monthly maintenance program.
Is my site surf, exposed or calm?
BlueScope's marine definitions bulletin, TB-35, uses Queensland examples. Surf means exposed to breaking surf and ocean spray: Bribie Island, Sunshine Coast and Gold Coast beaches, and Bargara. Exposed means open salt or brackish water facing onshore winds without typical breaking surf: Redcliffe, Cleveland, Moreton Bay, The Broadwater and Hervey Bay. Calm means protected water such as ports, harbours, bays and estuaries, including Gold Coast and Twin Waters canal estates.
Building on the Gold Coast, Sunshine Coast or near Hervey Bay? We specify cladding and fixings for your distance from the water.
Sheds on the Sunshine CoastFasteners, and the stainless screw mistake
Screws corrode too. BlueScope's fastener bulletin, TB-16, sets AS 3566.2 Class 3 as the minimum, suitable more than 1 km from marine influence, and Class 4 between 200 m and 1 km. Within 200 m it says to consult the fastener supplier, which is COLORBOND Ultra and SUPERDURA territory. A common error is to use stainless steel screws on a coastal shed to be safe. BlueScope states that stainless steel, copper and copper alloys are incompatible with COLORBOND and ZINCALUME steel; stainless fasteners are only for SUPERDURA Stainless.
Other things that shorten cladding life
- Areas rain never washes, such as walls under wide eaves, garage doors and the underside of gutters. BlueScope recommends hosing these down at least every six months, more often on the coast.
- What happens inside the shed. Heavy dust, emissions, heat, moisture, chemicals or animal housing can make standard cladding unsuitable.
- Contact with the ground: sheeting partly buried or in constant contact with soil or mulch.
- Condensation under the roof, which BlueScope says should be addressed at design stage with ventilation and a membrane or insulation.
Condensation: the corrosion that starts inside
BlueScope's bulletin CTB-11 explains that condensation forms when warm, moist air meets the underside of a roof sheet that has cooled overnight, and that significant condensation can cause damage that is hard and costly to fix after construction. Its recommendations are practical: ventilate so moisture can escape; drape a reflective membrane between the battens with at least a 20 mm air space above and below; use blanket-and-foil insulation for further protection; and trim insulation blanket well clear of gutters and valleys, because a wet blanket held against the steel can corrode it from underneath. The same membranes also reduce the popping noise roof sheets make as they heat and cool.
Warranties depend on location too
BlueScope's warranties are subject to application and eligibility, and warranty length depends on the end use and the location, including the nearest marine source. Its sample shed and garage warranty applies to a professionally designed and constructed structure on a concrete slab, with minimum sheet thicknesses and a minimum floor area. Ask your supplier how the warranty is registered, and check that the product chosen suits your distance from the water.
Requirements depend on your property, proposed structure and local planning/building controls.
Tell us how far the shed will be from the water and we will quote the right cladding and fixings.
Request a coastal shed quote