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Evaluating Structural Problems in Your Historic Building | Wisconsin Historical Society

General Information

Evaluating Structural Problems in Your Historic Building's Foundation

Evaluating Structural Problems in Your Historic Building | Wisconsin Historical Society

Your historic house or building has rested on its foundation for many years, so you should check periodically for signs of a developing structural problem. The most common structural problems are foundation settling, bowed foundation walls and damaged or failed masonry.

Foundation Settling

EnlargeA diagonal plaster crack coming off the corner of an interior door, a sign the floor has sagged.

A diagonal plaster crack coming off the corner of an interior door is a sign the floor has sagged. Source: Bob Yapp

You might find evidence of foundation settling in the form of diagonal cracks in the foundation or plaster, or sagging floors, windows or exterior doors. Settling of foundation walls happens when a foundation footing fails by sinking or moving laterally away from where it was originally placed in the ground. The footing is a wide masonry structure beneath a foundation wall that supports the wall, much like your foot supports your leg. The masonry wall on top of the footing sinks as the footing fails.

EnlargeImage of stucco garage with concrete block foundation that has severely settled.

From the exterior, you can see this stucco garage's concrete block foundation has severely settled. Notice the door casing has separated on the right hand side. Source: Bob Yapp

Foundation settling generally happens to historic houses and buildings when there is too much water built up around the foundation footings. However, the opposite can happen when a prolonged draught shrinks the soil around the footings.

A small amount of settling in a historic house foundation does not mean the foundation has failed. Often a foundation will settle in several locations within the first decade after construction, and then it never moves again.

Bowed Foundation Walls

If your foundation wall is bowing inward, you might also find these additional problems: sagging floors, windows and doors; cracked plaster; and buckled hardwood flooring. Your foundation wall could be bowing inward for several reasons. The most common cause is massive water build-up on the outside of the wall, which creates hydrostatic pressure. This pressurized water pushes the foundation wall inward.

Occasionally a foundation wall bows inward due to a large tree root. The root does not need to be pressing against your foundation to cause it to bow inward. A very large tree root 20 feet away from your foundation can shift the earth as it grows. This in turn pushes the ground between the root and your foundation, causing excessive pressure against your foundation wall.

If you have a rubble wall foundation, the bowed foundation wall could be caused by moisture entering the interior of the wall. This moisture can erode the mortar in the center of the wall, causing the fill to settle between the stones or brick. If your outside wall is straight and just the inside is bowed (or vice versa), then this may be the issue.

You should hire a professional structural engineer to evaluate your bowed foundation wall. In some cases, a mason may need to disassemble and reassemble, or even replace, a section of bowed foundation wall.

Damaged or Failed Masonry

Masonry foundations — whether brick, stone, concrete block or poured concrete — are prone to damage or failure of the masonry itself. If moisture gets into your masonry, it can freeze and crack or cause spalling of the bricks, stones or concrete.

If the mortar between your foundation bricks, stones or concrete blocks fails, your foundation walls could settle or bow inward. Repointing the masonry will be critical to restoring the health of your foundation.