How to Inspect a Slab for Defects: A Homeowner’s Guide

When buying, selling or performing routine maintenance on a home with a slab, it’s important to be able to identify damaged and/or future problem areas. The slab is the base upon which the entire structure sits, and any defects can lead to significant, costly repairs down the road. At Smith & Smith Home Inspections, we specialize in identifying these issues, which can save homeowners from unexpected expenses and give peace of mind.

Here’s a guide on how to inspect a slab for defects, with tips and insights from our experienced team of inspectors here in Murfreesboro, TN.

1. Understand the Types of Foundations and Common Defects

Before starting your inspection, it’s important to know what you’re looking for. There are different types of foundations used in home construction:

• Slab-on-grade: A single, thick layer of concrete poured directly on the ground. Common in homes built in areas where the ground doesn’t freeze.
• Crawl Space: A raised floor structure with a crawl space beneath it, which is typical in homes where the soil conditions or local climate dictate a different approach.

The most common defects associated with slabs include:

• Cracks: Surface cracks can occur from normal settling or changes in the ground, but larger or more severe cracks may indicate a deeper issue, such as foundation movement or soil instability.
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• Uneven flooring: If your floors are noticeably sloped or bumpy, it could be a sign of shifting or sinking in the slab.
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• Moisture issues: Dampness or visible water damage on the floor can signal a moisture problem coming from the slab, which might indicate drainage issues or even plumbing leaks under the slab.
• Popping or bulging: This can happen if moisture or pressure underneath the slab causes the concrete to lift.

2. Visual Inspection: Check for Cracks and Shifting

Start your inspection by walking around the exterior and interior of the home. Look for visible signs of cracks in the floor or foundation. Be sure to check the following:

• Cracks in the slab: Small, hairline cracks are common, but larger cracks (wider than 1/8 inch) or diagonal cracks should be cause for concern. These may be signs of foundation settling or soil movement.
• Uneven floors: Roll a ball or marbles across the floor in different areas to see if they roll unevenly. This can help you spot slight slopes or shifts in the slab that are not immediately visible to the eye.
• Cracks around doors and windows: If you notice doors or windows that stick, don’t close properly, or have gaps, it could be a sign that the foundation is shifting.

3. Examine the Exterior for Signs of Settlement

Step outside and carefully inspect the foundation and surrounding area. Look for the following:

• Cracks in the exterior walls: Horizontal or stair-step cracks can indicate significant foundation movement. Vertical cracks, while not always a cause for concern, should be monitored.
• Gaps between the slab and exterior walls: If you notice any noticeable gaps or separations between the slab and the walls, it could be a sign of slab movement.
• Low spots in the yard or standing water: Poor drainage around the foundation can lead to water pooling near the slab, which may cause the concrete to shift, crack, or erode over time. Ensure that the ground slopes away from the foundation to prevent water damage.

4. Check for Moisture and Water Damage

Excess moisture under the slab can lead to serious structural issues, including slab cracking, mold, or mildew growth. Inspect for the following:

• Visible moisture: Dampness on the floor, especially in crawl spaces, can be a sign of water intrusion under the slab. If you notice this, check the perimeter of the home for poor drainage or standing water.
• Musty odors: A musty smell in certain areas of the home may indicate mold or moisture problems beneath the slab, often due to poor ventilation or water leaks.
• Water stains: Look for water stains on walls, floors, or near plumbing fixtures. These stains could point to leaks from pipes beneath the slab or from poor waterproofing during the original construction.

5. Investigate Plumbing Issues

Plumbing lines often run under or through slabs, and leaks can sometimes go unnoticed until significant damage has occurred. Here are some ways to check for potential plumbing issues:

• Listen for running water: If you’re hearing the sound of running water when none is in use, it could be a sign of a hidden plumbing leak beneath the slab.
• Check water meter readings: If you suspect a leak, check your water meter when no water is being used in the house. If the meter continues to run, it’s a good indication that there’s a leak somewhere—potentially beneath the slab.
• Look for damp patches on floors: Localized wet spots on floors, especially around plumbing fixtures, can signal a plumbing leak under the slab.

6. Consider the Age and Type of Construction

When inspecting your slab, consider the age of the home and the construction methods used. Older homes may have concrete slabs that have shifted or cracked over time. Certain regions, including parts of Tennessee, may also have expansive soils (clay), which can shift or swell depending on moisture content and impact the foundation.

If your home was built in the past 20 years, you may also have a post-tensioned slab, a type of reinforced slab that uses tensioned cables to prevent cracks. These slabs tend to perform better under shifting soil conditions, but they still need to be inspected for signs of tension cable failure.

7. Professional Inspection

While you can perform a basic inspection of the slab yourself, it’s always a good idea to hire a professional home inspector—like the team at Smith & Smith Home Inspections. We use specialized tools and techniques to assess foundation health more accurately, including:

• Leveling equipment: To measure the degree of floor unevenness.
• Moisture meters: To detect hidden moisture in the slab or surrounding materials.
• Infrared thermography: To detect temperature differences that may indicate moisture or air leaks beneath the slab.

Conclusion

Your home’s foundation is essential for its structural integrity, and the concrete slab plays a pivotal role in this. By performing regular inspections and looking for early signs of defects, you can identify issues before they escalate into costly repairs.

If you are buying a house or selling your home, you need a professional home inspection. Contact us at Smith & Smith Home Inspections. We service Murfreesboro, Smyrna, Lebanon, Shelbyville, Manchester, McMinnville, La Vergne, Winchester, Woodbury, Columbia, Nashville or The Greater Middle Tennessee Area, and are committed to providing thorough, accurate, and reliable inspections to help you, your family and your investment.

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