Joist

A horizontal structural member used to form a floor or ceiling, spanning between supporting walls or beams. Floor joists carry the imposed loads (furniture, people) of the floor above. Timber joists in domestic construction are typically 47 × 195 mm to 47 × 225 mm C16 or C24 graded, at 400 mm centres. Engineered joists (I-joists, LVL) allow longer spans for open-plan extensions.