Dive summary:

• Would you believe a South and Central American hardwood that earns the same fire rating as concrete or steel and is three times harder than cedar and doesn't float?
• It's not new – some of it was used in the Coney Island Boardwalk in New York City – but ipe (pronounced ee-pay) may not be nearly was well known as its less-dense botanical cousins.
• Ipe costs about 30% more per linear foot than knotty pine or cedar, and its oils make it hard to paint, but it stiffly resists bugs, mildew and decay and can last a quarter-century. Some architects say that is more like 50 years, too.

From the article:

What natural building material is highly durable, resists flames and doesn't float? ...