A girder is a large structural beam that supports other smaller beams or joists at intermediate points, typically carrying more concentrated load than a standard beam and requiring its own dedicated support, whether columns, posts, or bearing walls positioned beneath it.
While the terms girder and beam are sometimes used interchangeably in casual conversation, girder often specifically implies a primary structural member carrying the load of multiple secondary beams or joists framing into it.
Because a girder concentrates so much structural load onto relatively few support points, its sizing and the design of those supports require particularly careful engineering attention.
What Does a Girder Involve?
- A large structural member, often steel or engineered lumber
- Support from columns, posts, or bearing walls beneath it
- Connections for multiple beams or joists framing into it
- Sizing calculated for the combined loads it carries
Why Are Girders Important?
By carrying the concentrated load of multiple smaller framing members, a girder allows a building to achieve larger open spans and fewer interior supporting walls than would otherwise be possible, a critical enabler for open floor plans in both residential and commercial construction. This load-concentrating role also means girder failure or inadequate support has more significant consequences than a failure in a single smaller beam.
Basement renovations that involve removing a support column beneath an existing girder require particularly careful engineering, since that column is often carrying a substantial share of the entire floor system’s load above it. This concentrated responsibility is why girder sizing and support conditions receive particularly close engineering scrutiny.
Girder vs. Beam
A girder is typically the primary, larger structural member carrying loads from multiple secondary beams or joists. A beam is the more general term for any horizontal load-carrying member, which can range from a small header to a large girder depending on its specific role.