A building joint is a junction where building elements meet without applying a static load from one element to another. When one or more of these vertical or horizontal elements that meet are required by the local building code to have a fire-resistance rating, the resulting opening that makes up the joint must be firestopped in order to restore the required compartmentalisation.
Such joints are often subject to movement. Firestops must be able to demonstrate the ability to withstand operational movement prior to fire testing. Firestops for such building joints can be qualified to UL 2079 -- Tests for Fire Resistance of Building Joint Systems.
The joint design must consider the anticipated operational movement of each joint. Timing is also important, as freshly poured concrete shrinks  particularly during the first few months of a new building, potentially causing joint size changes.
Where vertical fire-resistance rated wall assemblies meet the underside of the floor slab above, a movement joint results, which can be subject to compression, as the freshly placed concrete cures and shrinks all over a new building. This joint must be firestopped in a flexible manner.
- ^ "Cement Association of Canada - Drying Shrinkage". Cement Association of Canada. Retrieved 2008-05-05.[dead link]