Green Street Advisors notes that AFFO as a % of NOI varies by property type.

As Cap Ex takes a big bite out of cash flow, knowing the average Cap Ex as a % of NOI per property type is important to cash flow oriented investors. In the case of apartment buildings, Cap Ex takes 15% of annual NOI. Assume an apartment building is producing $10M

in NOl/year, what is the portion of NOl that is available to the REIT after Capital Expenditures?