Tests on floors at two houses of the Mark XI project under concentrated load were conducted in order to determine if changes in performance could be detected. The performance was compared to the response obtained at previous test of the sam floors by Onysko et al.(1981a) and to the response obtained by Onysko et al.(1981b) on floors that were dried in the laboratory. The increases in maximum deflections for the four floors studied are explained in terms of moisture content changes and differences between floors in material properties, joist spacing, span and loads. The effects of cross-bridging and strapping are discussed. Measures of the degree of load sharing and composite action are defined. It is concluded that a reduction of performance may be due primarily to an increase in moisture content in the subfloor with second order effects due to the reduction in effectiveness of cross-bridging and strapping.