rental units get charged more due to much greater liability. you have 20 renters in per year. what are the chances that one slips and falls,that somebody leaves the water on and it floods the downstairs,that somebody leaves the stove or grill on? you get the point its a much greater liability than the homeowner. as far as pilings in an x zone. we're 28 feet above sea level and in an x zone and have 4 foot pilings. i believe almost every home in watercolor is built on concrete pilings. as i said $300 is cheap to pay for peace of mind.