<P> Wood joists were also used in old - style timber framing . The invention of the circular saw for use in modern sawmills has made it possible to fabricate wood joists as dimensional lumber . </P> <P> Joists must exhibit the strength to support the anticipated load over a long period of time . In many countries, the fabrication and installation of all framing members including joists must meet building code standards . Considering the cross section of a typical joist, the overall depth of the joist is critical in establishing a safe and stable floor or ceiling system . The wider the spacing between the joists, the deeper the joist will need to be to limit stress and deflection under load . Lateral support called dwang, blocking, or strutting increases its stability, preventing the joist from buckling under load . There are approved formulas for calculating the depth required and reducing the depth as needed; however, a rule of thumb for calculating the depth of a wooden floor joist for a residential property is to take half the span in feet, add two, and use the resulting number as the depth in inches; for example, the joist depth required for a 14 ‐ foot span is 9 inches . Many steel joist manufacturers supply load tables in order to allow designers to select the proper joist sizes for their projects . </P> <P> Standard dimensional lumber joists have their limitations due to the limits of what farmed lumber can provide . Engineered wood products such as I - joists gain strength from expanding the overall depth of the joist, as well as by providing high - quality engineered wood for both the bottom and the top chords of the joist . A common saying regarding structural design is that "deeper is cheaper", referring to the more cost - effective design of a given structure by using deeper but more expensive joists, because fewer joists are needed and longer spans are achieved, which more than makes up for the added cost of deeper joists . </P> <P> In traditional timber framing there may be a single set of joists which carry both a floor and ceiling called a single floor (single joist floor, single framed floor) or two sets of joists, one carrying the floor and another carrying the ceiling called a double floor (double framed floor). The term binding joist is sometimes used to describe beams at floor level running perpendicular to the ridge of a gable roof and joined to the intermediate posts . Joists which land on a binding joist are called bridging joists . A large beam in the ceiling of a room carrying joists is a summer beam . A ceiling joist may be installed flush with the bottom of the beam or sometimes below the beam . Joists left exposed and visible from below are called "naked flooring" or "articulated" (a modern U.S. term) and were typically planed smooth (wrought) and sometimes chamfered or beaded . </P>

Name two types of wood from which joists are usually made