In conjunction with the tower's construction, in late 1905, Flagg was hired to design a westward annex to the Bourne Building and a northward annex to the original Singer Building. The Bourne and Singer buildings were to be united internally, and the old Singer Building was to be expanded to 14 stories. The top story of the Bourne Building would also be expanded so that it would cover the same area as the Bourne Building's lower floors. Plans for the Bourne and Singer extensions were filed in late 1906 and early 1907, respectively.