THE HOUSE DETECTIVE
Water under the house
DEAR BARRY: Since the last rains, I've had swampy soil under my house, with ponds and puddles in several places. Many of my neighbors have the same problem, and some have had serious building settlement and other moisturerelated damages. Fortunately, my house doesn’t seem to have had any water damage or foundation problems, but I’d like to prevent possible damage in the future. I've heard that added ventilation helps to keep the ground dry under a building, so I've installed screened vents between the crawlspace and the garage. Does this sound like an adequate solution, or could the problem be more serious? Matt
DEAR MATT: Problems with site drainage are common in many neighborhoods, and water in the crawlspace is a typical symptom. However, your attempted repair does not address the cause of the problem and has actually created an additional issue.
When the soil under a building is damp or moderately wet, cross ventilation, as required by the building code, is usually a sufficient remedy. In cases of excessive ground moisture, especially when there are ponds under the building, the water source must be discovered and eliminated or at least minimized. Unfortunately, the vent openings you have installed between the sub-area and your garage pose an entirely new problem. Each of these new openings is a fire-safety violation because it breaches the firewall between the garage and the dwelling. This is an important reason to hire a qualified professional to address your drainage problem.
To determine how water is getting under your home, the property should be evaluated by a geotechnical engineer to determine the drainage characteristics of the site and the most practical way of altering the direction of water flow. In some cases, drainage improvements can be as simple as changing the slope of the soil to redirect the water flow away from the building. Sometimes, French drains are needed around the building to enable buried rocks and piping to channel water to a more desirable location. Sometimes, it is even necessary to install sump pumps under the house to remove surface water by mechanical means.
As for ventilation of the sub-area, vent openings in the exterior walls may be sufficient for normal levels of ground moisture, but if high levels of humidity due to excessive ground moisture occur under a house, mechanical vent fans are sometimes needed.
In addition to addressing site drainage and subarea ventilation, you should also have the crawlspace thoroughly inspected for moisture damage. Although no damage has been apparent to you so far, a qualified home inspector may find conditions that have not yet been discovered. For example, there could be soil erosion, softening of the concrete, moisture condensation of the wood framing, dryrot resulting from moisture condensation, or rust damage affecting framing hardware, air ducts, electrical components, etc.
Flooding below a home is obviously not desirable, but moisture conditions can often occur without causing adverse effects. Most drainage problems are not serious in nature, but they can have serious consequences if not addressed in time by qualified experts. So have your property and sub-area professionally evaluated, and be sure to eliminate the vent openings in your garage firewall.