Capital improvement as far as the IRS is concerned is a major change to the underlying asset which extends the useful life.
the cost of that improvement, if made after the asset was placed in service, is listed as its own fixed asset and is depreciated using the same schedule as the parent asset, with a starting date of the date the improvement was completed. If that improvement was made to the property before you placed it in service then those costs are an addition to the property basis (cost)
Repairs are not capital improvements, they are an expense at the time they are paid for.
IRS pub 551, page 5, table 1
