TOKYO — Japan will start working toward possible legislation as early as fiscal 2016 to prompt the rebuilding of aging condominium buildings with noticeably high vacancies, according to sources.

The total number of unusable, empty houses and units in collective housing buildings has been predicted to increase to 5 million by 2025. The government intends to slow the pace with a series of measures and has set a target of curbing the increase at about 4 million by that year.

The government plans to obtain in March Cabinet approval on basic guidelines on housing policy for the next decade. The guidelines will include numerical targets and measures regarding vacant properties, the sources said.

According to the Land, Infrastructure, Transport and Tourism Ministry, the number of vacant properties nationwide stood at 8.19 million in 2013, of which about 40 percent, or 3.18 million, were unused as they could not be bought, sold or rented. The trend is expected to continue due to factors including the population decline.

For condominiums, the government will consider measures to facilitate easier rebuilding as their vacancies generally increase as they age.

Under the current Building Unit Ownership Law, a plan for rebuilding condominium complexes must be approved by four-fifths of the property owners, with non-responses counted as votes against.

With some owners unable to participate in the decisionmaking due to living long distances from their properties, the number of unresolved cases is said to be considerable.

The land ministry will consider legislation to allow resolutions to be made based only on expressed votes, the sources said.

Between 1975 and 2014, only about 250 condominium buildings have been rebuilt nationwide. The new policies aim to rebuild an additional 250 by 2025.

If houses and condominiums with advantages including being located within one kilometer of a station and only requiring small repairs are reused through such measures as resale, renting and renovation, it is expected that demand for those properties will rise and vacant properties will decrease.

In the aim of boosting occupancy rates, the government also plans to implement a system for issuing certifications for properties that have been vacant but renovated with improved quake-resistance and better design.

The government's goal is to double the size of the resale housing market from 4 trillion yen in 2013 to 8 trillion yen in 2025, the sources said.