The word “foundation crack” makes most buyers nervous. It is one of the items that can send someone into a panic when they read their inspection report. But not all foundation cracks are the same. Here is how we evaluate them and what you should understand.
Why Do Foundations Crack?
Concrete cracks. That is a fundamental truth about the material. All concrete experiences some shrinkage as it cures, thermal expansion and contraction with temperature changes, and minor movement as the soil beneath it shifts over time. Not all cracking indicates a problem. The questions are what type of crack, what size, what direction, and what pattern.
Types of Foundation Cracks and What They Mean
Hairline cracks: Very thin cracks, often less than 1/16 inch wide, that run vertically or at a slight diagonal are typically the result of normal concrete shrinkage and curing. They are very common in Portland homes and are generally not a structural concern. We document them but do not usually flag them as major defects.
Vertical cracks of moderate width: A vertical crack up to about 1/4 inch wide with no evidence of displacement is often still a settlement or shrinkage crack. It should be monitored and sealed to prevent water intrusion, but in most cases is not a structural emergency.
Horizontal cracks: These are the ones that get our attention. A horizontal crack in a poured concrete or concrete block wall can indicate lateral pressure from the soil outside pushing in on the wall. This is a potential structural failure mode, especially if the crack is accompanied by bowing or inward movement of the wall. Horizontal cracks should be evaluated by a structural engineer.
Stair-step cracks: These appear in brick or concrete block foundations and run diagonally along the mortar joints in a stair-step pattern. They indicate differential settlement. Small ones may be minor. Large ones or ones with significant displacement indicate a more serious settlement issue.
What Do We Do When We Find Foundation Cracks?
We document every crack with photos, note its dimensions and direction, and assess it in the context of the overall structure. Whenever we have doubt about the significance of a crack, we recommend evaluation by a licensed structural engineer. A structural engineer visit typically costs $300 to $600 for a written report and is money well spent when there is a genuine question about the foundation.
Portland’s Soil and Drainage Contribute to Foundation Issues
Portland has a mix of soil types. Expansive soils, which shrink and swell significantly with changes in moisture, are found in parts of the metro area. This seasonal movement puts stress on foundations over many decades. Poor drainage that keeps soil saturated against foundation walls increases lateral pressure.