What are Warré hives?
From Wikipedia, "Beehivee":
The Warré hive was invented by Abbé Émil Warré, and is also called "ruche populaire" (fr) or "The People's Hive" (en), the Warré hive is a modular and storied design similar to a Langstroth hive. The hive body is made of boxes stacked vertically; however, it uses Top Bars for comb support instead of full frames, as a general rule. The popularity of this hive is growing among sustainable-practice beekeepers.
The Warre hive differs from other stacked hive systems in one fundamental aspect: when the bees need more space as the colony expands, the new box is "nadired". i.e. positioned underneath the existing box(es). This serves the purpose of warmth retention within the brood nest of the hive, considered vital to colony health. The 1948 book "Beekeeping for All" by Abbé Warré has been translated from French in 2010 by Dr. David and Patricia Heaf and is available as a free download. More information on the Abbé and the hive is available at http://warre.biobees.com/bfa.htm