Similar to the double-web girder, the box girder consists of an upper and a lower chord, but they are connected to each other by two web plates arranged on the sides. The belts are made of solid wood or glued laminated veneer lumber and the side bars are made of wood fibre or OSB boards. Their advantage is their low weight and almost constant load-bearing capacity compared to a glulam truss with the same dimensions. In contrast to the double-web girder, the box girder can be used well for visible constructions.
Source: bauwion
