Did you depreciate the original price?

First, depreciation is only for value of structure, not the whole house price (excluding land).  So, if you depreciated the original property purchase price, you were wrong and you have to amend. all 4-5 years of tax return. 

My worry is you depreciated the whole purchase price. 

Second, If you only depreciate the structure, and your improvement is before placed in service date, there is no way (or evidence) to separate depreciation basis (value of structure) from improvement cost.  It's all lumped together.   And you can safely add improvement cost to the original purchase price.