All metals expand and contract with changes in temperature. Although steel is by far the least affected of all the metals commonly used for roof and wall cladding, the changes in length experienced in very long runs of roofing are significant.
On a clear hot summer day, with no wind, the steel temperature in roof cladding can reach approximately 50°C in COLORBOND® steel in colour Surfmist®, 60°C in ZINCALUME® steel and more than 80°C in COLORBOND® in colour Night Sky®.
Examples of the thermal changes in lengths of steel cladding that would result from various temperature changes in the steel are shown (see Table: Thermal expansion and contraction of steel cladding).
The actual expansion or contraction between the end of a sheet and the last support would only be a fraction of the figures shown because the movement in the length of fixed cladding would normally take place from the centre towards each end of the sheet. The movement at each end is thus only half the total expansion or contraction.
Transverse thermal expansion poses no problems in ribbed cladding because each rib absorbs some transverse movement.
| Sheet length (mm) | Expansion or contraction (mm) | ||
|---|---|---|---|
| 10°C change | 50°C change | 75°C change | |
| 5000 | 0.6 | 3 | 4.5 |
| 10000 | 1.2 | 6 | 9 |
| 15000 | 1.8 | 9 | 13.5 |
| 20000 | 2.4 | 12 | 18 |
| 25000 | 3 | 15 | 22.5 |
| 30000 | 3.6 | 18 | 27 |