HomeFit and the Healthy Homes Standards require you to have a groundsheet unless your crawl space is completely open to the elements. If you can get access to it, have a look under your house and see if there's any thick plastic sheeting on the ground.
Black polythene under a suspended floor. Credit: Allan McIntosh.
Subfloors often have vents like these. Check to make sure they are not blocked by weeds or other obstructions or painted over. Neither HomeFit nor the Healthy Homes Standards consider these vents to be sufficient to properly ventilate an enclosed crawl space like this. So they still need a groundsheet laid on top of exposed soil.
Open sided basements such as this, sometimes called pole houses, are well-ventilated and do not require a groundsheet.