The cost of the addition or improvement should be capitalized. The remaining net book value (NBV) of any replaced item(s) must be expensed. For a portion of an asset, the proportionate share of the asset replaced must be estimated and expensed. In some cases, it may be necessary to estimate the NBV of the current asset based on the "depreciated" replacement cost. If NBV of replaced items cannot be estimated, the cost of the replacement must be expensed.