A client once called me, worried because he'd found a thin, perfectly straight line that repeated in the same place on every level of his building. I told him that was good news. That line was the building doing exactly what it was designed to do.
Materials move. Concrete expands and contracts with temperature at a rate of about ten millionths of a degree Celsius per meter of length. It sounds insignificant until you multiply it: a 100-meter-long structure subjected to a 20-degree temperature variation between dawn and midday moves about two centimeters. That movement is going to happen. The only design question is whether the building has the space to accommodate it or if it will force its way through.
That's what joints are for. Expansion joints physically separate building sections and run through the entire structure. Control joints are induced in slabs and floors so that any cracks that will inevitably appear do so in a straight, planned line instead of diagonally across the room. Construction joints mark where one pour stopped and the next began. These are three different things, and confusing them on a construction site is costly.
In Latin America, there's an additional layer that can't be ignored: almost the entire region is seismic. The Dominican Republic, Mexico, Chile, Peru, Ecuador, Colombia, and all of Central America incorporate movement into their design equations. When a project has multiple sections, or when a new tower is built next to an existing one, the seismic separation between them is factored into the structural calculations. This separation is what prevents two sections with different vibration periods from colliding during an earthquake. The facade is addressed later, in that order.
What usually fails in practice is the seal. A well-designed joint system includes a flexible seal and a cover plate that allows movement without letting water in, and that seal has a lifespan. When it expires and no one replaces it, the joint becomes the building's main source of water ingress, and the water never reappears where it entered. That's why in the maintenance manuals we provide, joint seal inspections are scheduled by date, not based on individual criteria.
The other half of the work is architectural. A joint can be interpreted as a scar that bisects the facade or it can disappear within the composition. It aligns with a change in material, hides in a setback, or is made to coincide with the rhythm of the modular design. When the architect and the structural engineer decide on it together during the preliminary design phase, the joint becomes part of the design. When it is resolved on-site, it is always noticeable.
That's the bottom line. In the projects we manage, the joints are drawn up from the preliminary design stage, with the structural engineer and the architect at the same table, and detailed before a single construction drawing exists. That's the only point in the project where it's still free to move them.
A rigid building is a building that will crack where it shouldn't. A well-made one moves, and it moves in the way someone decided beforehand.
Recommended readings:
