How Moisture Exposure Damages Foundations

Residential water intrusion is a common peril that many homeowners contend with, and if it’s not addressed early, it can lead to serious structural losses above- and below ground. These losses may include mold growth, deterioration of organic construction materials, foundation gapping and cracking, wall failures, and uneven roof lines. Three of the primary causes of water-related foundation damage to be aware of are poor drainage, inadequate ground slope, and hydrostatic pressure. 

Inadequate Drainage

The external features of a home are – or should be – designed to direct water away from the structure. Downspouts are a key part of this system, carrying water from the roof and channeling it safely onto ground at least 5 feet away from the foundation. However, downspouts are often mistakenly directed to discharge much closer. 

Water is a powerful force, and over time it can infiltrate or erode the soil around the foundation and seep through the concrete and into the basement or crawlspace. Excess soil moisture contributes to foundation settlement, causing the house to sink. This moisture also leads to continuously damp wood that will begin to rot and degrade, which can cause the affected section of the house to shift.  

This section of downspout discharges directly into the soil adjacent to the foundation, and it has caused foundation damage.

Inadequate drainage can lead to another major concern – mold. 

Mold requires five conditions to flourish – a surface to grow on, air, moisture, an appropriate temperature (which varies between different species of molds), and dead organic matter to consume as a food source. Drywall and wood are common food sources for mold, which makes it particularly damaging to home interiors. Low light and low air movement are not required, but these are favorable conditions for mold, meaning that basements and crawlspaces are particularly susceptible to mold growth. 

The mold growth in this basement was caused by inadequate drainage.

Ground Slopes

Ground slopes, or grade around the home, is also a significant factor in foundation-related moisture problems. The International Residential Code requires a minimum of a 6-inch vertical drop for every 10 feet of ground away from a building’s foundation. This equates to a 5 percent slope away from the structure. If the ground slopes toward the home, rather than away from it, surface water drains into the soil around the foundation. This can do a lot of damage to foundation walls or supporting footings. As foundation elements shift, water intrusion can also occur into the crawlspace, or through gaps that develop between a basement wall and concrete slab. A reduction in foundation capacity results in building elements that no longer support the house, which could lead to interior and exterior cracking.

The surrounding ground slopes toward the home’s foundation at a rate of 7.7 percent, which is more than a 6-inch vertical drop toward the structure for every 10 feet of ground.

Hydrostatic Pressure

Hydrostatic pressure is the weight of resting water against a foundation or basement wall when the soil is saturated, either by poor drainage or flooding. This pressure is the result of gravity forcing water down into the soil, causing it to push against the structure. It increases with depth, meaning that more pressure is exerted on the bottom of a basement wall than the top. This pressure can be lateral or vertical, meaning it can twist structural elements, or push them up or down. 

Hydrostatic pressure can force moisture through pores in the basement wall and can crack and/or buckle walls. These damages can lead to serious structural losses above ground, including interior and exterior cracking in walls and wall coverings above weak points in the foundation, sections of the structure rotating in the direction of the pressure, and uneven roof lines.

This diagram illustrates the path water takes into a home when drainage is poor and hydrostatic pressure builds belowground.

It’s crucial to understand the source and duration of water exposure to address the underlying cause of loss. Donan is an industry leader in forensic engineering, providing objective conclusions that are sound and documented. Donan provides relevant information about losses and clear explanations about the perils involved based on close inspection, expert knowledge, and the scientific process. 

Submit a project to see how Donan experts answer questions about the cause of foundation damage or provide other mechanical, electrical, and structural solutions.