A dropped beam, or drop beam, is a critical component of home construction, as it fulfills an important structural need. Also referred to as a girder or a cantilevered beam, the drop beam provides additional needed support for framework such as the joists used for decks and roofs.
A drop beam is installed perpendicular to the joists (the horizontal boards or beams that support the framework) on any structural member. For example, if a row of joists is positioned north to south, the drop beams run east and west directly beneath the joists, providing them with a firm layer of support. Drop beams are nailed directly to the framework, so they don't require joist hangers of their own.
All joists are beams, but not all beams can function as drop beams, at least not individually. A drop beam must bear a very heavy load, so it will typically have the size of two or three joists combined. You can create a single drop beam by nailing two or three joists together, which provides the support necessary for the framework above.
A drop beam rests against the vertical posts holding up the joists. If installed properly, the beam should span horizontally along the foundation but stand vertically so the beam's flat side faces outward rather than up and down. To ensure the proper structural support, the top of the beam should rest firmly against the joists.
Not all structural members use drop beams for support, but drop beams have some distinct advantages over similar beams. For instance, drop breams can support the entire weight of a large frame using a minimal amount of material. Other types of joist supports, namely flush beams, require a complex arrangement of metal hangers for a less reliable support. Flush beams also serve to support the foundation, attaching directly to the joists with metal brackets. They depend on the stability of the joists just as the joists depend on the stability of the beams.