Re-roofing FAQs · Choosing your roof
How long can longrun roofing sheets be?
Long enough to run from ridge to spouting on almost any home. Each sheet is rolled to the length of its run, so there's no join down the slope. The Code of Practice doesn't set a single maximum. On long roofs, what limits a sheet is expansion in the heat, the profile, and getting it to site.
What happens on long runs
- Expansion. Steel grows about 12 mm for every 10 m of sheet over a 100°C temperature swing. Over a 60°C range, a 30 m sheet moves about 21.6 mm.
- The 20 m rule. Runs over 20 m fixed into timber or hot-rolled steel need provision for expansion.
- No end laps if possible. The Code says to avoid them. Where a sheet is too long to transport, a step joint can replace the lap.
- Profile capacity. The Code flags run lengths after which a profile's capacity should be checked: 15 m for standard corrugate, and longer for deeper ribs.
Does a normal house need joins in the sheets?
Rarely. Most house roof runs are short enough for one sheet each.
Written by the CTR Roofing team, Hamilton. Updated October 2026.