On a visit to Holland some years ago, photographer Camilo Vergara was depressed by the sameness of the housing developments inhabited by Dutch workers. It sparked memories of something different in the older working-class neighborhoods of the United States.

"Transformed Houses," an exhibition of Vergara's photographs and text panels put together by a team of architectural historians, is the result. The exhibition, circulated by the Smithsonian Institution Traveling Exhibition Service, will be on view at Baltimore's Peale Museum through Dec. 13.

The exhibition focuses upon a type of housing that goes little noticed by architects and planners or members of the design profession generally -- ordinary houses, usually constructed upon wooden frames, put up for families whose breadwinners worked in nearby factories in the industrial cities of the Northeast and Midwest -- and it demonstrates the oft-amazing changes in style and character these houses have gone through under a succession of owners.

Many of these changes were physically necessary simply to keep the houses from falling down. Others were occasioned by needs for more space, a child's bedroom, for instance, or a "mother-in-law" addition. Still others were the result of changes in "lifestyles" -- a front yard paved over to provide parking space for a new car. Most of the changes were done without outside "design" guidance, other than that, say, of an agent for an aluminum siding firm.

Some of these changes are surprisingly beautiful, some approach folk art, some are inept. The main point of the show, however, is well taken. These changes represent a record of self-help and self-improvement that is economically significant. Taken together, they often create a vigorous, vernacular kind of streetscape that would be the envy of many a contemporary architect, planner or developer.