Conversion mania grips Manhattan as more prime office space turns into apartments

Last year saw twice as much Manhattan office space start to be converted into apartments as the year before – a boom that’s poised to change the chemistry of Midtown neighborhoods historically dominated by office towers, hotels and entertainment venues.

Among them: at least four buildings on Third Avenue in the East 40s and 50s and 135 E. 57th St. at Lexington Avenue, once a symbol of the late-1980s office-development craze. The conversions will bring 24/7 energy and domestic warmth to blocks that are typically quiet after dark.

On the other hand, RXR’s conversion of 5 Times Square into 1,250 apartments — which was one of the quartet of West 42nd Street towers that proclaimed a new era for the “Crossroads of the World” — might have a calming effect on the frenetic street scene around i