What is the main support under a wood deck called?

The main support under a wood deck is referred to as a girder. In the context of deck construction, the girder serves as a foundational component that supports the frame and distributes loads from the deck to the posts or footings below. It is typically larger and stronger than the joists, which are the horizontal supports that run perpendicular to the girders. The girder forms the framework that provides stability and strength to the entire structure, making it integral to the overall safety and durability of the deck.

Other components, such as beams and posts, play important roles as well, but they do not serve the same primary function as the girder in supporting the overall structure beneath the decking surface. The posts, for instance, are vertical supports that transfer the load from the girder to the ground, while joists support the decking itself but are primarily focused on the span between girders and do not provide the overarching support system that the girder does. Recognizing the specific roles of these components is crucial in understanding deck construction and design.