Kit sheds are popular because they arrive pre-designed and pre-cut. But the engineering that comes with the kit is only valid for the conditions it was designed for. If those don't match your block, the shed may not be safe, and a certifier can't approve it.
Why wind is the main concern
A steel shed is light compared with a house. That makes wind the governing load in most designs. Strong wind pushes on the walls, sucks the roof upward and tries to rack the frame sideways. If any connection fails, roof sheets and frames can come loose and damage property next door.
The National Construction Code (NCC) requires structures to resist the loads they are likely to experience, including wind. Part H1 of NCC Volume Two covers this for Class 1 and Class 10 buildings. For most steel sheds, wind loads are worked out using AS/NZS 1170.2, the Australian and New Zealand standard for wind actions.
What the wind rating depends on
A shed's wind design depends on where and how it sits. The main factors are:
- Wind region. Australia is mapped into regions with different design wind speeds.
- Terrain category. Open paddocks expose a shed to more wind than a suburban street full of houses.
- Shielding. Nearby buildings can reduce wind, but only if they are permanent and the right size and distance.
- Topography. A shed on a hilltop or near the crest of a slope sees higher wind speeds.
- Importance level. The NCC links the design risk to the building's use and the consequences if it fails.
Openings matter too. A large roller door left open in a storm can let wind pressurise the inside of the shed, which increases the uplift on the roof. Good engineering assumes the worst case for door positions unless the design says otherwise.
What to check on the engineering certificate
Before you buy, or before you lodge for approval, check that the supplier's engineering:
- Names your site address or states design parameters that suit it.
- Matches the exact shed ordered, including size, height, door sizes and positions, and any added awnings or mezzanines.
- Includes footing details and states the soil conditions assumed.
- Is signed by a qualified engineer.
Footings are a frequent gap. Standard kit footings often assume firm natural ground. On fill, reactive clay, sloping or wet sites, the footings may need a site-specific design.
How certification works for a kit shed
A small shed may be exempt development if its size, height and boundary distances all fall inside the Codes SEPP caps. See Shed size limits for building without approval in NSW. Exempt sheds must still comply with the building code or be structurally adequate, so the engineering still matters.
A larger shed needs a complying development certificate (CDC), or else council approval plus a construction certificate. For either, the certifier will want:
- A site plan showing setbacks, boundaries and other buildings.
- Elevations and floor plans for the shed as ordered.
- The engineering certificate and footing details.
- Information on stormwater disposal and, where relevant, bush fire construction.
During construction, inspections are needed at set stages, such as after excavation for footings and before reinforced concrete is poured, plus a final inspection once the shed is complete. Our guide to Critical stage inspections: what we check and when explains the full list.
Changing the kit after approval
Swapping a roller door for a larger one, adding a skillion or moving openings can change the wind design. If the shed changes, ask the supplier for updated engineering and tell your certifier before building. Approved plans and the built shed must match.
CertifiBuild certifies sheds and outbuildings across NSW. Read more on our sheds and outbuildings service, have your plans and engineering checked before lodging, or book an inspection at least 48 hours ahead.
Local help across NSW
CertifiBuild certifies Class 1 and Class 10 work in 39 council areas. Local rules on these council pages are a good place to start: Camden Council, Hawkesbury City Council, Woollahra Municipal Council, Kiama Municipal Council, Wollongong City Council, Lithgow City Council.
Suburb pages with local planning notes: Catherine Field, Clarendon, Currans Hill, Darling Point, Jamberoo, Kembla Grange, Kiama, Leppington, Lithgow, Marrangaroo. You can also browse every service area.
Sources
- Part H1 structure, NCC 2022 Volume Two (ABCB)
- AS/NZS 1170.2:2021 Structural design actions, Part 2: Wind actions, Standards Australia
- Fact sheet on exempt garden sheds, cubby houses and similar structures, NSW Department of Planning