Expansion joints
Breaks in the tile field are required on most large area installations to compensate for variable rates of expansion between the substrate and the tiles above it. Expansion joint requirements depend upon several factors, including climate and substrate, and are specified by an architect.
Insert joints wherever two different substrates abut. For glass wall tile, leave a 1/4 in. gap between the perimeter tile and the wall. Expansion joints should be filled with caulk after the tiles are grouted. There are standards, such as ANSI's 108 AN 3.7, that give advanced instructions on expansion joints.