The I-house was first recognized as a recurring vernacular house form by Fred Kniffen of Louisiana State University. He coined the name in 1936, deriving it from the fact that the house form was often found in the midwestern states of Indiana, Illinois, and Iowa. Kniffen also recognized that the term was appropriate since the profile of the core house form, which consists of two main rooms set side-by-side on the first story and a matching pair on the upper story, has a distinct vertical orientation that suggests a capital I. Most commonly in the South, a central passageway separates the main rooms on both stories. The I-house is a vernacular house type characterized by a recurring physical form rather than by features associated with any particular architectural style. Stylistic features were applied to the recurring form and changed over time in keeping with popular tastes.
The origins of the I-house are unclear. Some scholars believe that it is derived from sixteenth-century English antecedents, while others think that it is an American form related to log-building traditions. The I-house emerged as a recognizable form in Pennsylvania, Delaware, Maryland, and Virginia by the 1750s and in the Carolinas by the 1780s. By the end of the eighteenth century regional variations of the basic I-house form had emerged. I-houses with porticoes and small porches tended to dominate in Virginia, while single-story, full-width porches or galleries were widespread on the I-houses of the Piedmont area of the Carolinas and Georgia. In the coastal areas of the Carolinas many I-houses featured full-width porches on both stories.
The I-house form appeared in Mississippi around 1800, brought to the Natchez area by settlers from the Eastern Seaboard. The I-house was widely built throughout Mississippi in the antebellum period, reaching the peak of its popularity and consistency of form in the 1840s and 1850s. Most Mississippi I-houses are wood-frame buildings with weatherboard siding. Brick I-houses are much less common and are located mostly in towns, with the highest concentration in Holly Springs.
I-houses in Mississippi are generally categorized into several subtypes on the basis of porch configuration and the arrangement of rooms beyond the core form. These subtypes include
- basic I-house with no porch
- I-house with one-story portico
- I-house with monumental portico
- I-house with double-tiered portico
- I-house with composite porch (combining a one-story, full-width porch and a two-story or monumental portico)
- single-galleried or Carolina I-house (one-story, full-width porch)
- double-galleried I-house (two-story, full-width front porch)
- full-colonnaded I-house
- I-house with dual overlapping colonnades
Of these subtypes, the most popular were the monumentally porticoed, single-galleried, and double-galleried variants. The porticoed I-house was preferred in the northern third of the state; the single-galleried I-house was preferred in the central and southern uplands; and the double-galleried I-house was most prevalent in the southwest corner of the state, in and around Natchez.
I-houses continued to be built after the Civil War but declined in popularity after about 1875 because of changing architectural tastes and technologies. Few were built after the turn of the twentieth century.
- Richard J. Cawthon, The I-House and Expanded I-House in Mississippi, 1800–1875: Variations of a Traditional Form (1992)