The firm's trademark style of discreet brick and limestone townhouses in neo-Georgian style is embodied in the Benjamin N. Duke House at 1009 Fifth Avenue, one of a row of four houses built in 1899-1901 for the speculative builders William and Thomas Hall.
Welch was the consulting architect in restorations made to a number of designated historical landmarks, including Alexander Hamilton's Hamilton Grange in the Hamilton Heights neighborhood of Upper Manhattan, George Washington's Headquarters in White Plains, New York, and the Dutch Colonial Dyckman House in Inwood, Manhattan.