dead load

Dead load is the permanent weight of a building or structure itself: the concrete, steel, timber, brick, mechanical systems, and any fixtures bolted down for keeps. Unlike live load (people, snow, wind), dead load does not move or change once construction is complete. It acts downward continuously and must be supported by the foundation, beams, and columns from the moment the structure stands.

In practice, dead load includes the weight of the floor slab, roof deck, exterior walls, interior partitions, permanent HVAC equipment, electrical conduit and wire, plumbing, and ceilings. A typical reinforced concrete floor slab weighs around 150 pounds per square foot. Steel beams, curtain walls, and hung ceilings add more. The structural engineer must calculate these weights precisely because they determine how large the beams, columns, and foundations must be. Underestimate dead load and the structure will deflect excessively or fail. Overestimate and you pay for unnecessary material.

Dead load is distinguished from live load, which is temporary and moving: occupants, furniture, snow accumulation, equipment that can be removed. Seismic load and wind load are dynamic; dead load is static. In seismic design, however, dead load matters because heavier structures develop larger inertial forces during shaking. Building codes specify minimum live loads (40 psf for offices, 100 psf for retail), but dead load must be calculated from actual materials chosen.

The term 'dead' reflects the load's passive, non-moving character, as opposed to 'live' load which can shift or be shed. This vocabulary comes from 19th-century engineering, when the distinction clarified how to size beams and foundations. Dead load governs the sizing of the primary structure; live load governs the design of decks and local elements. A change in architectural finishes or building materials changes dead load and can require structural redesign.