The proposal looks straightforward on a slide: an underused office tower, a housing shortage, a conversion. Architects who have run the numbers describe a much narrower set of buildings for which it works.
The constraint is geometry. Apartments need windows. A floor plate more than about thirty-five feet from window to core produces interior space that cannot legally be a bedroom and is expensive to make useful. Office buildings from the 1970s and 1980s were designed with deep floor plates precisely because office work did not need daylight at every desk.
Older buildings, counterintuitively, convert better. Pre-war towers were built before air conditioning and fluorescent lighting, when every workspace needed a window, which produced narrow floor plates and operable windows — nearly ideal residential geometry.
Downtown Minneapolis has a handful of such buildings. Several have already been converted, some successfully.
Beyond geometry, the obstacles are plumbing and structure. Office buildings concentrate plumbing in a central core; apartments distribute it to every unit, requiring new risers through every floor. Residential building codes impose different fire separation and egress requirements. And older structures often need seismic or load upgrades to satisfy current code.
Cost estimates for conversions in comparable markets run between three hundred and five hundred dollars per square foot, which is competitive with new construction only when the building is acquired cheaply.
That acquisition price is the sticking point. Office building valuations have fallen but not always to the level conversion requires, in part because owners with patient lenders prefer to wait rather than realize a loss.
City officials have discussed incentives: tax increment financing, property tax abatement, expedited permitting. Each has been used elsewhere with results that depend heavily on whether the underlying building was a good candidate to begin with.
"Subsidy can close a small gap," an architect who has studied several downtown buildings said. "It cannot move a window."
The buildings that do not convert present the harder question. A 1980s tower with a deep floor plate and declining occupancy has few second uses, and demolition in a dense downtown is expensive and slow. Several cities are quietly studying what a long-term vacancy strategy even looks like.
