My paper will provide an architectural history of the La Perla settlement, Puerto Rico’s most famous “slum.” At the same time it will point to the opportunities and limitations of writing a history of informal architecture, which until very recently has been neglected by architectural historians or at best subsumed by a concern with vernacular or community-built construction.

La Perla is a hundred years old and located next to the walled city of Old San Juan, one of the oldest European settlements in the Americas. Since La Perla is unusually well documented in its different historical stages one would expect it to be a convenient subject for historical analysis. Nonetheless writing La Perla’s architectural history leads to several challenges, which question the usefulness of traditional historiographical tools for informal architecture, and to a great extent also the formal-informal distinction itself.

La Perla’s buildings have always been closely connected to the “formal” houses in the adjacent Old San Juan. Although erected without planning permission they were designed following similar typologies and often built by the same craftsmen. They were laid out according to a logic of property development and economic opportunity, and responded to similar policies that were also applied to the “formal city.” Their inhabitants tended to work in the formal city, were subject to comparable types of ownership and tenancy agreements, and sometimes even paid property tax.

My paper will look at La Perla’s architecture in the context of both traditional Caribbean and modern precedents as well as against the background of changing urban design policies. At the same time it also problematizes the formal-informal distinction, which habitually has put structures such as La Perla on the wrong side of scholarly hierarchies.

I argue that the terms “formal” and “informal”, for La Perla and beyond, are historical rather than analytical categories. They first appeared with a moral undertone in the 1930s, along with slum clearance and modernization strategies that converted the US territory of Puerto Rico, which is situated at the interstices of “developed” and “developing world,” into a much-touted “laboratory of modernity” and showcase of US development policy. And the distinction became less and less pronounced with the crisis of functionalist architecture and planning and the increasing acceptance of La Perla’s design characteristics from the 1970s onwards.

Along those lines my paper contends that a history of informal architecture has to question the categories and distinctions that constituted the discourse on architectural modernism, and that the scholarly analysis of buildings such as La Perla’s has to be based on an expanded field of architectural historical research.