A wall or roof of a trailer are formed from a first panel and a second panel which are joined together by a cap and a strip which interengage. The cap includes a base wall and an interlock provided thereon. The base wall abuts the outer surfaces of the panels. The strip includes a base wall and an interlock provided thereon. The strip and cap are separate members. The base wall of the strip abuts the inner surfaces of the panels. The interlock of the strip and the interlock of the cap mate together to form a joint. The interlocks extend between the panels. The panels may be composite panels or may be from a single sheet or multiple sheets of metal. An adhesive may be provided between the base wall of the cap and the outer surfaces, and an adhesive may be provided between the base wall of the strip and the inner surfaces.