Larger kitchens, bigger baths, and remodeling mania are expected to fuel increased demand for countertop material to the tune of 509 million square feet by the year 2009, according to The Freedonia Group, a Cleveland-based industrial market research firm. But a slowdown in single-family housing starts may keep sales increases to a modest 1.7 percent annually. The strongest gains are anticipated in sales of natural and engineered stone.