Wisconsin Historical Society

General Information

Historic Building Foundations

Historic Building Foundations | Wisconsin Historical Society
EnlargeStone foundation

Brown County. A stone foundation with rope joints. Source: WHS - Historic Preservation - Public History.

To identify problems with the foundation of your historic house or building, it will be helpful for you to understand how your foundation was constructed. To understand your foundation’s construction, you should know these three things:

  • Functions your foundation serves
  • Type of foundation you have
  • Building material your foundation is made of

Functions of Your Foundation

Your foundation is the structural base of your historic house or building. Your foundation is made up of a masonry wall that sits on a masonry footing. This footing is at least one-third wider than the wall. The footing distributes the weight and prevents the wall and building above from sinking into the ground.

Ideally, the foundation footings installed under your house or building were set below the frost line. The frost line is the deepest point that frost settles into the ground during the winter. If your footings were not installed below the frost line, the movement of the frozen ground could heave and shift your footings and foundation walls. This heaving and shifting can cause cracks, wall settling, upward wall movement or bowing in the wall and concrete floor. Frost lines vary from north to south across Wisconsin. In southern Wisconsin, the frost line is at 40 inches; in northern Wisconsin, the frost line is at 48 inches.

Foundation Types

Your historic house or building foundation may be one of the following three basic types. Each foundation type has a different construction and footing.  

  • Full Basement Foundation. A full basement foundation typically includes basement ceilings that are tall enough for an adult to stand up in and windows. These foundations are constructed with brick, stone, concrete block or poured concrete. Concrete floors are present under the entire structure. Access to the basement is provided from either an interior first-floor basement staircase, or from an exterior basement staircase accessed from outside the structure. Some older houses have a hard-packed dirt floor instead of a concrete floor. A full basement foundation has interior walls that rise from a floor to the wood joists of the first floor. Therefore, the frost footings are closer to the floor than those in a crawl space foundation without a basement.  If you have this type of foundation, you will have a lot of masonry wall to monitor for bowing, cracks and other failures.
  • Full Crawl Space Foundation.
    EnlargeFoundation section

    Illustration of a typical basement in Wisconsin. On average, the frost line is 4'-0" below grade. Source: WHS - Historic Preservation - Public History

    A full crawl space foundation has no basement. Instead, the space between the first floor and the dirt below it is usually so small that you have to crawl to get into the space under the floor. Access is usually provided through a hinged trap door in the floor. These foundations are constructed with brick, stone, concrete block or poured concrete. Full crawl space foundations are rare in Wisconsin. The ones that exist are generally found under some of the oldest houses or buildings in the state. Full crawl space foundations provide less access to the bottom of the foundation walls that rest on top of the frost footings. As a result, repairs will require more digging because the mason will be unable to see as much of the interior foundation wall as with a full basement foundation.
  • Partial Full Basement. A partial full basement is simply a combination of a full basement foundation and a crawl space foundation. The extent of the full basement varies. In earlier houses, the basement is a small portion that was used as a root cellar. Later houses could have a full basement under most of the structure with a crawl space under just the rear one-story portion or under an addition. Partial full basement foundations are typically constructed with brick, stone or concrete block.

Foundation Building Materials

The foundations under Wisconsin historic houses and buildings are constructed with several different types of materials. Many of the problems that occur with different construction materials are similar, but you’ll be in a better position to identify unique problems if you know something about the material used to construct your foundation.

  • Stone. If your historic house or building has a stone foundation, it will be constructed with limestone, sandstone or different types of field or river stones. Limestone and sandstone are a softer type of rock. To determine whether your stone is limestone or sandstone, use a screwdriver to scratch a stone in an inconspicuous interior place. Limestone will scratch with a bit of effort, while the even softer sandstone will scratch with little effort. The color of these stones ranges from off-white to red, with shades of beige being the most typical colors. Field and river stone foundations are made up of many types of stones and rock that vary in color and tend to be more rounded in shape. These stones are much harder than limestone or sandstone and will not scratch as easily.
  • Brick. Your house or building has a brick foundation if the interior walls are made up of hundreds of uniform-sized clay bricks with uniform mortar above, below and beside each brick. Bricks range in size on their face from 8-1/2 inches wide x 2-1/2 inches tall to 7/12 inch wide x 2-1/4 inches tall. Most bricks are red, but the color can vary from off-white to brown to dark red. Each brick wall is measured in wythes. Wythes are essentially layers of brick that make up the thickness of a wall. For example, a three-wythe brick wall is three bricks thick, which could measure between 18 and 21 inches thick.
  • EnlargeConcrete block foundation

    Brown County. Here is a foundation made with concrete block. Notice that the foundation is made with both smooth face block as well as with a molded face to mimic stone. Source: WHS - Historic Preservation - Public History.

    Concrete Block. Your house or building has a concrete block foundation if your foundation blocks are uniform in size and the face of the blocks measures 14 to 15-1/2 inches wide x 6 to 8 inches tall. Some concrete block foundations have a face that looks like stone. These mass-produced stone-faced concrete blocks imitate the look of stone at a lower cost. If your blocks are painted, you can use a screwdriver to scratch away some of the paint and look at the raw surface. If you see small stones, you probably have a concrete block foundation instead of a stone foundation.
  • EnlargePoured concrete basement wall

    Dane County. Poured concrete basement wall that was board-formed. Notice the horizontal lines indicating the size of boards used. Source: WHS - Historic Preservation - Public History.

    Poured Concrete. Your house or building probably has a poured concrete foundation if:
    • Your house or building was built after 1900.
    • Your foundation walls in the basement or crawl space show signs of horizontal lines with wood grain embossed into the face of the wall between the lines.