Archaeological deposits build up inside standing buildings both under and between floors and these have the potential to provide considerable information about human behavior in the past. Under and between floor spaces provide a unique depositional environment that allow the survival of rare and fragile organic materials that typically do not survive in other archaeological contexts, including paper, cardboard, fabric and other fibres, seeds, leather, and human hair and skin cells. However, they require a clear understanding of depositional processes to allow their interpretation. Experimental archaeology was conducted to understand the process of artifact deposition and the interpretation of underfloor deposits in twelve standing buildings in Western Australia. Floors were built and a range of artifacts swept across them to determine how artifacts travelled across floorboards or fell through gaps between boards. Size, shape, and angularity of artifacts were key determinants of the likelihood of deposition. Sweeping activity makes it more likely that material will be deposited around the margins of rooms, and particularly, to either side of doorways. Underfloor deposits excavated from two specific Western Australian buildings, Ellensbrook Homestead, and the York Residency Museum, are interpreted based on the results of these experiments.