Foundation Crack Patterns Common in St. Louis Area Homes

The St. Louis area sits on deep deposits of loess (wind-blown silt) overlying clay and limestone bedrock. These soils are highly moisture-sensitive, and foundation movement is common when soil moisture conditions change.

Vertical Cracks

Vertical cracks in poured concrete foundation walls are often related to concrete shrinkage and may not be structurally significant if they are narrow and stable. However, vertical cracks that widen over time, or those accompanied by water intrusion, should be evaluated by a structural engineer.

Horizontal Cracks

Horizontal cracks are the most structurally concerning pattern. They typically indicate lateral soil pressure against the foundation wall, a condition that can worsen over time. Horizontal cracks in masonry block walls warrant prompt evaluation because they can indicate wall bowing that may eventually require reinforcement.

Stair-Step Cracks

Stair-step cracks follow the mortar joints in masonry block or brick foundations and can indicate differential settlement. These cracks are most significant when:

• •They are widening over time
• •They are accompanied by wall displacement
• •They appear alongside other signs of movement (sticking doors, sloping floors)

Masonry Cracking in Older Neighborhoods

In St. Louis's older brick neighborhoods, cracking along mortar joints in above-grade masonry walls can also indicate foundation movement. A structural engineer can determine whether masonry cracking is cosmetic (thermal movement, aging mortar) or structural (foundation settlement below).