ABSTRACT
Rules of thumb were used before 'scientific' methods of design and have been recorded in early carpenter's manuals. The sizes recommended for floor joists and beams present a diversity of rules and, during the change from oak to fir, show a poor understanding of structural behaviour, but comparison of the various tables suggests that the intention behind them all was to limit the liveliness of the floor. Experiments at the beginning of the nineteenth century provided the means for a more rational approach to the same problem, enabling designers to use different timbers and to size members in order to limit the deflection for given loads.
