Modern homes often use engineered lumber or kiln-dried wood. As this wood dries out completely after construction, it shrinks, causing gaps and cracks at connection points [2].
Immediate attention is required if the crack is widening, diagonal, jagged, or if you can see a gap between the stair stringer and the floor joist. Warning Signs of Structural Danger: The stairs feel bouncy or unstable. The gap is widening over time. The trim around the top of the stairs is pulling away. How to Fix a S4U Stair Crack (Top) s4u stair crack top