Irish soda bread typically relies on baking soda (sodium bicarbonate) as the leavening agent, which reacts with the acidic ingredients like buttermilk to create carbon dioxide bubbles that help it rise. If your soda bread didn't rise at all, it's possible that the baking soda was expired or not enough was used, the dough may have been overmixed (which can deflate the gas bubbles), or the oven temperature might have been too low. Checking these factors should help troubleshoot the issue for your next attempt!