There are two main subcategories of home aviaries: grounded aviaries and suspended aviaries. Grounded aviaries are affixed to the ground with a concrete base to prevent rats and other vermin from entering. Suspended aviaries are suspended in the air with only the 'legs' of the aviaries affixed to the ground; hence, the need for a protective base is eliminated in suspended aviaries. Most grounded aviaries typically feature a woodwork or PVC frame unlike the metal frame of public aviaries; however, it isn't uncommon for suspended aviaries to feature a metal frame.