Determine proper solution for water under house

Q. The home I'm buying has a drainage problem under the building. Whenever we have heavy rains, there is standing water several inches deep in the crawl space. The seller said this can be fixed by drilling holes in the foundation wall at the downhill side of the building. To me, this sounds like an amateur solution to a serious problem. Do you think drain holes in the foundation are a good idea?

A. Your concerns are well-founded. Drain holes in the foundation wall, as suggested by the seller, may be an adequate drainage solution in some situations, but this approach does not provide a full remedy in every case. Some site drainage problems have complexities that require more than mere evacuation of surface water from the crawl space.

Rather than attempting an assumed solution, evaluation of the problem by a drainage specialist, such as a geotechnical engineer, is advised to ensure the totality of the problem is adequately addressed.

If you drill drain holes in the foundation, as suggested by the seller, three assumptions are being made:

• It is assumed that all groundwater in the subarea will flow to the drain holes and that there are no low areas under the house where standing water could remain.

• If you simply drain the ground water from beneath the house, it is assumed that water flow under the building is not causing soil erosion at the piers and foundations. Ongoing erosion can lead to eventual undermining of the structure. Therefore, a prime consideration is prevention of further water intrusion, not merely the evacuation of surface water.

• If you pay exclusive attention to the drainage and ground conditions, potential moisture damage to the building itself could be overlooked. For example, excessive ground moisture could cause condensation on wood framing members and hardware, resulting in fungus damage to joists, blocking and subfloor, as well as rusted metal fasteners. Therefore, the need for preventive measures such as increased ventilation of the subarea and/or a vapor barrier on the ground should also be considered.

This is why a comprehensive evaluation of the situation, under and around the building, by a licensed geotechnical engineer is advised. A determination should be made as to the source of groundwater entry. A drainage system outside the building may be needed to prevent water entry, rather than merely trying to expel groundwater after it has entered the crawl space. If expulsion of groundwater under the building is necessary, a sump pump may be needed, rather than or in addition to drain holes in the foundation. Only a drainage specialist is qualified to determine which methods of correction are appropriate.

Once the subarea has been cleared of excess ground water, have the subfloor and wood framing thoroughly reviewed by a licensed pest control operator (termite inspector) and by an experienced home inspector. Then you will know whether past moisture conditions have caused any damage to the building.

• To write to Barry Stone, visit him on the web at www.housedetective.com, or write AMG, 1776 Jami Lee Court, Suite 218, San Luis Obispo, CA 94301.

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