This paper presents the results of in situ quasi-static tests on a full-scale wood floor diaphragm in a two-storey woodframe house. The main objective of the study was to investigate the in-plane flexibility/rigidity of the diaphragm. Fourteen different diaphragm and structural configurations were investigated. The main parameters considered in the study included the nail schedule, panel-edge blocking, sub-floor adhesive, perpendicular walls above and below the diaphragm, and wall finish materials. The results indicated that panel-edge blocking increased significantly the diaphragm shear stiffness, particularly for diaphragms without sub-floor adhesive. Also, the presence of perpendicular walls acting as additional chord members caused a significant increase in the flexural stiffness of the diaphragm. The design procedure included in the Uniform Building Code (UBC) to compute in-plane diaphragm deformations was assessed by comparing its predictions with the experimental results. The UBC predictions agreed well with the experimental results for some configurations, but the correlation was poor for others.Key words: diaphragms, floor, tests, wood, wooden structures.