How do I determine the Cost Basis on a 30 yer old house that I recently converted to a rental. What information do I need. I formerly used the house as my primary residence.

[NCperson]

the cost basis is what you originally paid for the house plus any improvements you made since then, 

the age of the house is immaterial, when you bought the house is what is material. 

[AmeliesUncle]

The Basis for depreciation is the LOWER of (1) the Adjusted Cost Basis [usually purchase price, plus cost of improvements, minus depreciation (if any)] and (2) the Fair Market Value when it was converted to business/rental property.