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Barry Stone, Homeowner has swamp under house

DEAR BARRY: Every time it rains, the crawlspace under my house becomes a swamp, with ponds and puddles everywhere. Several of my neighbors have the same problem, but I’ve crawled under my house with a flashlight, and there doesn't seem to be any water-related damage.

A contractor friend told me that added ventilation will help to keep the ground dry, so I've installed screened vents between the sub-area crawlspace and the garage. Does this sound like an adequate solution, or could the problem be more serious and complicated?

— Matt

DEAR MATT: Your question raises four specific issues:

• Finding the cause of the groundwater problem.

• Finding the solution to the groundwater problem.

• Determining whether the building has been damaged.

• What to do and what not to do to resolve and prevent damage.

Excess groundwater is a common problem in many neighborhoods, typically resulting from faulty surface-drainage conditions. In some cases, this can be due to the inherent geology of the locale. Other times, it is the result of faulty grading of the site, during or after construction. Although faulty drainage is an undesirable condition, correction is not always necessary, depending upon whether moisture-related damage is taking place or is likely to occur.

To determine why the crawlspace below your home is becoming a seasonal swamp, you should consult a drainage specialist, such as a geotechnical engineer or a licensed contractor who specializes in the evaluation and correction of ground-drainage issues.

An expert of this kind can assess grading conditions that affect water movement on your property. In some cases, repairs can be as simple as changing the slope of the soil to redirect surface drainage away from the building. If more complicated upgrades are needed, such as sump pumps under the building or French drains near the building, a drainage expert can advise you accordingly.

To determine whether water-related damage actually has occurred, professional inspections are preferable to a cursory examination of your own. A licensed general contractor or a qualified home inspector should conduct a thorough evaluation of the conditions under your home.

The foundations should be checked for cracking, decomposition and signs of settlement. The ground surface should be checked for possible soil erosion; wood members should be inspected for damage, deterioration and evidence of moisture condensation; and hardware components should be examined for possible rust damage. Additionally, a licensed pest control operator should inspect wood members for possible fungus infection, which commonly occurs when there is excess moisture under a building.

Additional vent openings can help to keep the subarea dry, as advised by your contractor friend, but they will not eliminate the underlying problem of water intrusion. A better reason for increased ventilation is to prevent moisture condensation on structural components.

However, vents should be open to the outside of the building, not to the garage. Venting into the garage, as mentioned in your letter, constitutes a fire safety violation, because those vent openings breach the required firewall between the garage and the dwelling. This is just one more reason to seek professional advice before attempting repairs of your own.

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