Expansion joint

An expansion joint is a movement gap formed by separating a building or element completely along a set line. Concrete and other materials expand and contract with temperature, shrink as they dry, and the ground may settle differently under different parts of a building. If that movement has nowhere to go, the structure opens its own joints in the form of cracks. In Turkish the term is dilatasyon derzi.

Why and where joints are used

Very long buildings, junctions between blocks of different heights, places where different foundation types meet, and L-, T- or U-shaped plans are typical cases that need one. In seismic regions the joint width is calculated in the structural design so the two blocks cannot pound into each other during shaking. The joint runs from foundation to roof, with columns and beams resolved separately on each side.

Detailing the joint

• On facades, floors and roofs the gap is closed with flexible, watertight cover profiles that allow movement.
• Pipes crossing the joint need flexible connections.
• Inside, the joint line disappears when floor finishes and ceiling layouts are planned around it.

Designers often turn expansion joints into a feature on the facade, marking them with a change of material or a recess. Placing these lines correctly in a visualisation model keeps the facade faithful to what will actually be built.