Foundation Elevation Surveys Explained: How Pros Measure Movement (and What the Numbers Mean)

• A foundation elevation survey measures height differences across your slab to detect movement.
• Small variations may be normal — large differentials can indicate foundation repair is needed.
• Elevation readings help determine whether cracks are cosmetic or structural.
• Professional foundation inspection ensures accurate measurements and repair recommendations.
• Understanding the data helps homeowners make informed slab foundation repair decisions.

A foundation elevation survey is the first step toward protecting your home from foundation movement, slab settling, and soil erosion. It uses detailed measurements to determine whether the home has shifted, so the foundation can be repaired and leveled to prevent future movement that could severely damage the property.

What Is a Foundation Elevation Survey?

A foundation elevation survey is a diagnostic assessment of the home’s foundation. It measures the height of the concrete slab or pier and beam foundation across the property to determine if it is level or settling in areas. During the evaluation, a professional will use several tools to record the elevation, including a zip level, which monitors the elevation between foundations, around corners, and across various terrain, and a digital altimeter, which uses atmospheric pressure ratings to measure the altitude of the structure. 

These instruments record the height of the entire layout of the property, including support walls, interior floors, and the home’s exterior. Advanced technology makes it easy for one person to collect all the necessary readings in a few hours or less. The tools automatically log the measurements for the homeowner and the crew making the repairs.

Why Do Foundation Companies Use Surveys Before Repairs

Homeowners and crews must complete a thorough foundation inspection before making any repairs. These readings are essential because they inform the work that needs to be done to address any underlying foundation problems. They illustrate how the foundation has moved, where support is needed to level the home, and the risk for future shifts based on the soil quality. The professionals can then create a detailed work order outlining the steps that need to be taken so that the homeowner can make an informed decision.

Why Foundations Move in Texas

Foundation problems are all too common across the Lone Star State. However, the extent of the damage and the types of problems that occur vary across different regions. Many areas have high concentrations of clay soil, which expands and contracts as moisture levels change. The expansion-contraction cycle can cause the foundation to be uneven in some areas, leading to bowed walls, sloping floors, structural cracks, and doors and windows that won’t close. Excess rainfall, poor drainage, and plumbing leaks can worsen these issues by inundating the soil with moisture.

How Professionals Measure Slab Movement

To measure slab foundation movement, professionals collect benchmark points for the property to establish its existing height. Measurements are taken at various intersections and corners inside and around the home. The data is used to create a detailed 3-D contour map of the property to identify high and low points in the foundation. A follow-up inspection is done to determine whether the foundation has shifted since the last inspection. Any sloping, sinking, or shifting can then be addressed through foundation leveling or by adding additional support beams and walls under or around the house.

What Do Elevation Differences Mean?

Elevation differences across the property can be a sign of concern if they exceed acceptable tolerances. Excessive shifting or settling can lead to structural damage that could severely damage the home or make it unsafe to inhabit.   

The two main categories analyzed include tilt and flexural deflection. A tilt of 1%, or 1 inch across 100 inches, and a deflection of L/360, or 1 inch across 360 inches, are considered acceptable. Foundations can also withstand vertical drops in elevation plus or minus ¾ inches, so the elevation may vary up to 1-1/2 inches across the floor plan (Post-Tensioning Institute, 2015). Any greater drop is considered excessive and will likely be repaired with foundation leveling. If the drop exceeds these limits and no other signs of distress are detected, the shifting is likely due to the home’s original construction and not foundation problems. However, uneven settling and shifting may need to be addressed to retain the home’s structural integrity. Site surveyors should use engineering judgment to assess acceptable limits for the home. 

Properties tend to be more sensitive to horizontal shifting, which can cause cracks and gaps in the floor that make room for excess moisture and pests. Any horizontal shifts of over 1/8 inch should be repaired to seal the foundation and prevent the cracks from widening (Simms, 2021). 

Elevation surveys can help determine if the cracks are cosmetic and a result of everyday wear and tear or structural, which may require extensive foundation repair. Not all elevation changes are signs of foundation problems. Seasonal changes in moisture levels can cause minor shifting. Moving into a home can also cause it to settle due to the added weight. What’s known as the “settling in” period can last 12 to 24 months as landscaping watering comes online (Post-Tensioning Institute, 2015).

When to Schedule a Foundation Inspection

Homeowners should schedule a foundation elevation survey if they suspect shifting, settling, or sloping in or around the home. Common warning signs include:

• Cracked concrete slab foundations
• Sticking doors and windows
• Openings that won’t close
• Sagging or sloping floors
• Cracks in the walls or floors
• Bowed walls that appear to curve
• Uneven roof

These signs may only indicate foundation problems if they are accompanied by elevation changes, which is why it’s important to schedule a baseline elevation survey as soon as they appear.

Repair Options Based on Survey Results

Once the survey has been completed, the crew will lay out the homeowner’s options for repairing the foundation based on their findings. Possible remedies include concrete slab foundation repair, which may include polyjacking the slab to make it level, or pier and beam foundation repair, which can include waterproofing the crawl space beneath the home or adding support beams to reinforce the foundation. 

Depending on the survey findings and whether any noticeable signs of distress are present, the crew may advise a wait-and-see approach. The professionals will return at a later date to complete another survey to see how much the foundation has shifted before making repairs. Other cases may require foundation maintenance to prevent future settling.

If you are concerned that your home may require foundation repairs, contact Perma Pier for a free foundation inspection to begin the evaluation process. The sooner you start recording the elevation, the sooner you can secure your home.

FAQs:

1. How much foundation movement is normal?

Foundation movement is considered normal if the vertical elevation drop is within 1-1/2 inches across the property. This may occur during the settling-in period.

2. How do I know if my slab foundation needs repair?

Foundation repairs are necessary if the elevation drops below the acceptable tolerances and signs of distress are evident around the property. 

3. Are elevation surveys included in foundation repair costs?

All our foundation elevation inspections are free and are included in the foundation repair costs. Homeowners do not have to pay extra to have their foundations inspected.

4. Can I measure foundation movement myself?

No, elevation surveys require professional expertise and industry tools that increase expertise. We provide the engineering judgement to help you make an informed decision based on the findings.

Sources: 

Post-Tensioning Institute. (2015). Evaluation Guidelines For The Performance Of Slab-On-Ground Foundations, First Edition 2015. https://www.post-tensioning.org/Portals/13/Files/PDFs/Events/Conventions/TechnicalSessions/2015/042815Brumley.pdf

Simms, D. (2021, November 30). Foundation Cracks: What’s Normal and When to Worry. Angi. https://www.angi.com/articles/quarter-inch-crack-my-foundation-major-concern.html