According to this article, if you have 80% of the units vacant and do significant capital upgrades, you can destabilize the building.
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That is, if 75 percent of the building-wide systems (i.e., there are a total of 17 building systems, including, among others, plumbing, heating, fire escapes, elevators, kitchens, bathrooms, pointing or exterior surface repair) are completely replaced when the building is 80 percent vacant, units subject to rent stabilization can be deemed permanently exempt and converted to free market status.
In addition to at least 13 of the 17 building systems that need to be upgraded, all ceilings, flooring and plasterboard or wall surfaces in common areas must be replaced; and ceiling, wall and floor surfaces in apartments, if not replaced, must be made as new as determined by DHCR.
From a valuation perspective, buildings that are at least 80 percent vacant will likely begin trading at a significant premium if they can qualify for the building-wide system improvements.
For example, a six-unit building with five-vacancies is 83 percent vacant and an investor would likely go through the Substantial Rehabilitation process to deregulate the vacant apartments. This building would trade for a significant premium to a comparable six-unit building with fourvacancies (i.e., 67 percent vacant and not eligible for the Substantial Rehabilitation exemption), as a purchaser in this instance would have to underwrite based on cash flow from the existing legal rents.