Good read

[Guest]

Understand that moving from 2.4GHz band to 5GHz band would require 2 to 3 time more APs to provide the same coverage, it is law of physics. Additionally if the goal is to provide the highest possible 11ac rates everywhere, you would need to increase the AP density by another factor of 2-2.5. Consider this when budgeting for your next upgrade.

http://www.extremenetworks.com/understanding-fccetsi-dfs-regulations-for-802-11ac-deployments/