Q. We just had a heavy rain, and our crawl space is filling up with water. Our sump pump has been running, and we noticed a small geyser from the side of the pit. We received estimates for either a French drain around the crawl space, with two more pumps, or adding another 4 inches of concrete on top of our crawl space slab to hopefully seal out the water. Which do you recommend?
A. Your question came in four times in the same day from different people, after another heavy rain. The ground saturates, and water levels are higher until water sifts through the soil, follows the water table, flowing to ever-lower points, and evens out. After continual rain episodes, flooding occurs because water continues to accumulate above ground with no lower point to percolate to.
There is a misconception that raindrops seep right into the ground where they land. Although five drops out of 100 do that, the other 95 flow to a lower point. I look for the low points in a yard, and often see where well-meaning landscapers have piled topsoil around plants or created slightly sunken planting beds near a foundation. They don’t understand that after plants get sufficient moisture to their roots, the remaining water goes right to the foundation, gets drawn into the concrete wall by capillary action and ends up in the basement or crawl space.
This problem is compounded by the rain gutter and downspout installers who choose where to direct the water. They should never direct water to an inside corner, where walls join at an L, but they do. They also direct too many roofs, or too much roof, to one downspout, which causes the water to immediately back up, overflow the undersized gutter, slap down onto the ground or hard surface, cause erosion and pond where it lands next to the foundation. Then there’s the problem of a lack of wall waterproofing, from the joining of the foundation top to the wall above all the way to the roof overhang. Water can even penetrate the wall at the second story, and make it all the way down the wall interior and into the basement or crawl space.