A fully depreciated asset cannot be revalued because of accounting's cost principle.
Definition of a Fully Depreciated Asset
A fully depreciated asset is one that has accumulated depreciation equal to its cost. Hence, the book value of the asset is $0. Once an asset is fully depreciated, there will be no additional depreciation expense.
Example of a Fully Depreciated Asset
Let's assume that a company purchased a building more than 30 years ago at a cost of $600,000. The company then depreciated the building at a rate of $20,000 per year for 30 years. Today the building continues to be used by the company and it plans to continue using it for many more years. The company's current balance sheet will report the building at its cost of $600,000 minus its accumulated depreciation of $600,000 (a book value of $0) even if the building's current market value is $2,000,000.
Unless there are improvements to the building, there will be no depreciation expense after the 30th year.