An income house is a multi-apartment residential building constructed to rent out apartments—a type that took shape in European countries by the 1830s–1840s. Apartments were usually grouped around stairwells, corridors, or galleries and tended to be uniform in plan. Income houses of the late nineteenth and early twentieth centuries typically had a small inner courtyard-well; the rest of the lot was occupied by the building itself, with utility rooms often below the courtyard. As a rule, only the principal façade facing the street received full decorative treatment. Owners could be private individuals or institutions seeking steady income—schools, orphanages, monasteries, and both commercial and charitable societies. Purpose-built income houses began to be erected in Saint Petersburg in the mid-nineteenth century and make up a significant part of the city’s pre-revolutionary fabric. By the early twentieth century, about 80% of the city’s buildings were income houses, fitted with the most advanced systems—lifts, steam heating, and electricity—and boasting functional, carefully considered layouts.