Depreciation Basis Reduction

Hello,

I have a rental property and am depreciation the cost basis for the structure. I have replaced the roof and added the costs to my basis. However, I want to reduce the depreciation basis by the amount attributable to the old roof. For example, the original depreciable basis is $350,000 and the amount attributable to the old roof is $5,000. How do I reduce the depreciable basis from $350,000 to $345,000?

I would appreciate your suggestion.