How to Find the Cause of Most Home Structural Failures

By: Doug Hastings, ASHI Certified inspector, ACI
Updated: January 29, 2018

Approximately 90% of all structural building failures are caused by moisture. This problem is clearly the number one enemy of any home. Regardless of age, style, or location of a home, moisture is extremely damaging. All homeowners, home buyers, home inspectors, and real estate professionals need to be able to recognize it.

House Structure and Moisture

To understand why moisture causes so much damage, it’s important to understand what the structure of a house is.  The “superstructure” of a building has four parts:

1. Foundation
2. Floors
3. Walls
4. Roof

Moisture can easily enter these spaces from either outside or inside of the building. Home inspectors should methodically go through the entire house searching out this most elusive nemesis.

Is Moisture Recognizable?

Sometimes moisture is visible on the surface of building materials, making it easy to recognize; but many times, it is located in concealed spaces behind the finished building materials that are not visible to the untrained eye. The longer dampness remains unchecked, the more damaging and expensive it becomes to remedy. 

Looking for Moisture: Start in the Basement and Then Go Outside

We will launch our tour together in the basement or crawl space, seeking moisture, figuring out its source. The most common dampness in below-grade foundations originates from outside the building. Moisture intrusion is caused by inadequate control of surface and ground waters. The results can be discolored walls, seepage on the floor around the perimeter of the foundation, or a completely flooded basement.

So what causes these conditions?

The most common cause of basement moisture is improper landscaping. Simply put, the earth grading is sloped towards the foundation. This is called negative slope. The first step in managing surface water is to make sure the earth slopes away (this is positive slope), from the foundation on all sides of the building. Even the smallest depressions or settlement of soil can trap water, allowing it to dampen the walls and stain the foundation.

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Common Grading Defects

Although type of soil can have an impact on whether surface water will enter the building, there are three common grading defects:

1. Flat or negative slope: The minimum positive slope should be 48:1 for non permeable surfaces like a driveway and 12:1 for permeable surfaces like grass. Anything else causes moisture to head to the foundation.
2. Settled backfill: In this scenario, the backfill between the foundation wall and the perimeter has settled below ground level. Water from the downspout then flows back toward the foundation wall and penetrates into the basement.
3. No drainage swales: Drainage swales direct surface water away from the foundation in situations where the overall lot drainage is toward the house. Without them, water is going to travel to the foundation.

Home inspectors should look for these defects and inform homebuyers if they’re present and why they should be corrected immediately.

So, we see that landscaping is a problem, but is that the only thing on the outside of the home that causes moisture intrusion? I’ll answer that question in another article coming soon.

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If you like the idea of searching out problems like moisture and landscaping issues to make sure home buyers are aware of what they’re purchasing, consider becoming a home inspector. You can check out our home inspection education offerings here.