Sheet metal gauge is deliberately confusing: the bigger the number, the thinner the sheet. A 30-gauge sheet is thicker than 28, which is thicker than 32.
What thickness actually does
- Thicker sheets span further between purlins without sagging
- They drum less in rain and dent less under foot traffic
- Coating systems last longer on stiffer, flatter steel
- They cost more per metre and add load — modestly, but it adds up
Where thinner is acceptable
Light-gauge (often 28/30) corrugated sheets are fine on sheds, temporary structures and tightly spaced purlins where the budget genuinely cannot stretch. They are not a defect — specifying them as if they were premium residential sheeting is.
What to ask for
Write the base metal thickness (BMT) in millimetres on the order, not just the gauge — gauge standards vary between manufacturers. For a family home, err on the thicker side; the roof is the one component you cannot easily replace later.