The Navy has more than 175,000 buildings and other structures on its bases. Altogether, those facil￾ities cost billions of dollars each year to maintain—but funding for their maintenance has regularly fallen short of amounts that the Navy estimates would keep them in working order. As a result, the Navy faces a backlog of deferred maintenance. The costs of performing that maintenance and further renovating and modernizing the Navy’s deteriorated buildings may be significant.In this report, the Congressional Budget Office analyzes the condition of roughly 20,000 buildings that the active Navy (excluding the Navy Reserve and the Marine Corps) uses and maintains on its bases (also called installations) in the United States. For that group of buildings, CBO estimated two types of costs: • The cost of eliminating maintenance backlogs and raising the condition of the buildings to the Navy’s standards would be $17 billion (in 2020 dollars), and • The cost of renovating and modernizing the buildings within their current footprint (the area they cover on the ground) to fully support their users’ missions would be an additional $32 billion.On average, completing those buildings’ maintenance and their renovation and modernization would cost nearly half as much as replacing them altogether.CBO based its estimates on the most recent data provided by the Navy, which were current as of September 2020. Since then, the prices of goods and services in the United States have risen consid￾erably, so the costs of maintaining and renovating Navy buildings have probably increased as well— and may continue to rise, especially if inflation persists. The estimates of costs in this report do not account for those effects, nor do they account for the effects of current efforts to modernize facilities in the Navy’s shipyards.