If you improve depreciable property, you must treat the improvement as separate depreciable property. Improvement means an addition to or partial replacement of property that adds to its value, appreciably lengthens the time you can use it, or adapts it to a different use.
You generally deduct the cost of repairing business property in the same way as any other business expense. However, if a repair or replacement increases the value of your property, makes it more useful, or lengthens its life, you must treat it as an improvement and depreciate it. taxmap/pubs/p946-006.htm#en_us_publink1000107379
You repair a small section on one corner of the roof of a rental house. You deduct the cost of the repair as a rental expense. However, if you completely replace the roof, the new roof is an improvement because it increases the value and lengthens the life of the property. You depreciate the cost of the new roof.taxmap/pubs/p946-006.htm#en_us_publink1000107380
You can depreciate permanent improvements you make to business property you rent from someone else.