A flitch beam (or flitched beam) is a compound beam used in the construction of houses, decks, and other primarily wood-frame structures. Typically, the flitch beam is made up of a steel plate sandwiched between two wood beams, the three layers being held together with bolts. In that common form it is sometimes referenced as a steel flitch beam. Further alternating layers of wood and steel can be used to produce an even stronger beam. The metal plate(s) within the beam are known as flitch plates.
Because flitch beams are significantly stronger than wood alone, they:
Flitch beams can also be created from existing in-situ joists or beams permitting easier renovations.
Due to the high cost of labor, use of this type of beam has greatly declined. The advent of high-strength engineered lumber which uses modern adhesives and lower cost wood fibers has rendered this system largely obsolete. For example compare the capacity of 2 beams spanning 18 feet: the allowable strength of a 3½ʺ × 11¼ʺ laminated veneer member has a tabulated allowable applied load of 398 plf (pounds a linear foot); compare this to a 2 × 12 flitch beam constructed of ½ʺ steel plate with two laminations of #2 SPF with an allowable applied load of 386 plf
The engineered lumber is cut to length and installed similar to sawn lumber; the flitch requires shop fabrication and/or field bolting. This coupled with a much increased self weight of the beam (11.4 lbs for engineered wood vs. 25.2 lbs for flitch) decreases the viability of the system.