The owners of this 1870 house used Sanborn maps to re-build an original porch. (Fran Weichart)

The wraparound porch on Fran Wiechart's house is the room that she and her family use more than any other in their 1870 Stick Style Evanston, Ill., residence. Wiechart reads the newspaper and mail on the couch, and her husband and children eat dinner around a table during the summer while screens keep the bugs at bay.

But it wasn't always that way. More than a year ago, Wiechart had a crumbling stoop, not a porch. She had always suspected that her home once had full-fledged porch because other houses on her street, built during the same era, have porches. In fact, Wiechart's house was the only one of two on the block without the distinctive verandah associated with the Victorian era. In her eyes, the house didn't look right. It was tall and skinny, set far back compared to its counterparts.

So when the stoop's staircase began crumbling, Wiechart started to think it was time to replace it—or rebuild that porch. So she and her husband, John, stopped by the Evanston Historical Society to find out more about their house. They found a Sanborn Fire Insurance Map from 1890. "Sure enough, there was a wraparound porch," she recalls. She figured that was a sign that she and John should restore the outdoor room. "We should do it. It was meant to be," she told him.

More homeowners interested in restoration are referring to the Sanborn maps, drawings created for insurance company underwriters, according to Grace DuMelle, president of Chicago-based Heartland Historical Research.

Sample Sanborn map, used with permission from The Sanborn Library, LLC

D. A. Sanborn started the company in Manhattan in 1867 to show a building's fire risk. Each map showed all the buildings on a town block, what materials were used for construction, and whether the building was commercial or residential—and even whether there were nearby fire hydrants or water tanks.

Sanborn employees traveled around the country, pasting changes on existing maps until they created newer versions. By the time Sanborn died in 1883, the company had surveyed about 12,000 cities and produced about 700,000 maps nationwide. The Sanborn Co. flourished until the 1950s, when the insurance industry came up with new ways to gauge risk that made the maps obsolete. The Connecticut-based company continues to provide mapping services and geographic information.

The vintage Sanborn maps are now providing a wealth of information to homeowners intent on restoring their residences to their original appearance. They are most useful for dating a house if a building permit is unavailable, or determining whether there are missing staircases or newer additions.

Tools for Professionals

Urban planner Doug Kaarre, a staff liaison to the Historic Preservation Commission for Oak Park, Ill., which oversees any changes to residences in the town's historic district, often calls the local historical society to date houses he believes were built before the village was incorporated in 1907. If the home is on the 1895 Sanborn map, he knows it's at least that old.

Kaarre also likes the maps because they can indicate not only the type of porch on a house, but whether it was open or closed, useful information for the commission, which wants to ensure that any future additions are compatible to houses within historic districts. He also likes to find out how old additions are. For example, the commission doesn't have jurisdiction on a 1950s addition on a Victorian home because anything built after 1940 doesn't contribute to the district.

The maps are invaluable in another way, according to DuMelle. "If you've got a house on the map that was multi-family, and you want to make it single-family, it's helpful to know that there was no central staircase, and there were fire escapes on the side," she says. It's also beneficial for a homeowner to learn if there was a previously a town dump on the premises because he will probably want to remove any contaminated soil.

How to Find Sanborn Maps

The maps are available in a digitized black-and-white format at university libraries, historical societies, public libraries, and sometimes state preservation offices. Hard-copy versions are also at the Library of Congress, Chicago History Museum and the University of Illinois at Chicago. It's useful to look at the original color maps: a house shaded in blue means it was built from stone. Pink means brick; yellow, frame construction; yellow with gray border, ironclad frame; and orange, fireproof construction, says DuMelle.

DuMelle has had several clients over the years who wanted to learn more about their residences from the maps. One client who restored a single-family dwelling had always been curious about the garage, since it resembled a house with its windows and transom doorway. The map showed that the garage had once been a residence, which was confirmed once a neighbor tore down an adjacent carport, revealing bricked-over windows on the garage.

Architect Christopher Rudolph, who specializes in restoring old houses, made a similar discovery while restoring an 1888 Queen Anne wood-frame house originally owned by the Armour family in Chicago's Hyde Park. A Sanborn map from that era showed there was a smaller porch, so the architect opted to recreate the historically correct addition.

For the Wiecharts, the old documents not only confirmed their hunch, they were a tool that enabled them to win over the Evanston Historic Preservation Commission. Since their home is in a historic district, they needed a variance and a certificate of appropriateness to recreate that porch. The old document allowed them to do both.

Tearing down the old stoop also revealed a previously hidden colored-glass transom over the front entryway. The new porch, designed by architect Anne McGuire, is slightly larger than the 1870s version to accommodate furnishings. "Now we seem to hang out in the front yard more. It seems more neighborly, like it used to be," Wiechart says. "I've met more new people because I've been out on the front porch."

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