What Is a Tongue-and-Groove?

Tongue-and-groove boards interlock edge-to-edge to form the smooth, finished ceiling common in cedar pavilions.

Tongue-and-groove (T&G) is a milling profile in which each board’s protruding tongue fits the next board’s groove, creating a tight, continuous surface with no gaps. In pavilions it forms the finished underside of the roof — the clean vaulted ceiling seen between exposed cedar beams.