1.   The boards overhead buckled and dropped little clouds of dust as great thumping steps wandered around the office.

2.   If there were no gap, the boards would buckle when they expanded.

3.   Sometimes boards will buckle when there is no expansion joint between them and the wall, so the boards have no space to expand into when they swell.

4.   Without that gap, the boards would buckle when they expanded.

5.   Without this gap or joint, the boards can buckle.