Depreciation calculation starting date?

As per excise audit we have reversed cenvat credit on capitive consumption for canteen building in sep-2011.

Now the same reversal amount we are going to be capitalized in Fy-2011-2012. But the basic amount of canteen building we capitalised in FY.2010 -2011 only .So please clarify, from which date we have to calculate the depreciation.