They say a house is only as strong as its foundation. While it's true that a bad roof or shoddy plumbing can set your building back a lot of money, a foundation in disrepair can put the entire structure at risk, and can cost tens—even hundreds—of thousands of dollars to repair. Since it's literally underground, your foundation is easy to ignore, but its health is crucial. A little bit of education from the professionals can go a long way toward raising building administrators' awareness of the importance of a sound, well-maintained foundation.
What's Under There?
Every region has its own architectural history, and Chicago is no different. Foundations can often be one of the best ways to date a house or building. According to James Collins, an architect at the Oak Park-based architectural and engineering consulting firm Criterium Collins, the older housing stock still found in the city have foundations that “are basically wooden piers going down to one piece of stone. They're what we would call ‘Chicago cottages’ built in 1870s and 1880s.” At that time, transporting goods was still an elaborate and expensive process. Every step of home construction was also done by hand, giving builders limited options. By the turn of the last century, these wooden frames rotted out, says Collins.
To fix the issue, builders tried a new technique. “In the 1910s, they started to pour concrete around those posts and to form a little more of a basement. Original basements were originally a couple feet with a dirt floor. They would come back and dig down to the bottom of the structure, and pour concrete around those posts,” says Collins. Eventually though, the wood inside the concrete rotted out as well. Brick and limestone became the norm by the 1890s before concrete began, and builders used sand-based mortar. “By the 1910s, poured concrete foundations became more common than stone,” says Collins.
According to Collins, the mortar used with the brick, limestone and concrete blocks, has shown its weakness decades later. “Early mortar was basically lime and sand. Over time, water leaches out the lime, so they're all slowly deteriorating,” he says.
Materials are not the only variable in building foundations. Surrounding soil also plays a large part of whether a foundation keeps its integrity. Soil composition varies incredibly throughout the country. In the South, the earth is rich in clay that expands when wet, which can make foundations very difficult to maintain. The Chicago area's ground contains some clays, but also a lot of sand, which holds together better than clay. Sand compresses well, and can hold its structure around a foundation.