Most Chattanooga homes sit on a crawl space, and most crawl spaces sit on clay. When a summer storm drops two inches in an hour, that clay stops absorbing almost immediately and the water goes looking for the lowest point on the lot. Very often that point is under your house. If you have puddles on the vapor barrier, a musty smell in the hallway after rain, or an encapsulation company quoting you a sump pump and a dehumidifier, read this first. The cheapest fix is usually outside, not inside.
Crawl space water in this area comes from three places, in this order of likelihood. Roof water dumped at the foundation. A single downspout on a 2,000 square foot roof can put out several hundred gallons in one storm, and if it discharges onto a splash block six inches from the wall, most of that goes straight down along the foundation. Grade sloping toward the house. Landscaping beds, settled backfill and a decade of mulch can quietly reverse the slope so surface water runs at the house instead of away from it. Uphill runoff on a sloped lot. On the hillside neighborhoods around Signal Mountain, Lookout Mountain and Missionary Ridge, water sheets down from the lot above you and your foundation is the first wall it meets.
A sump pump removes water that has already reached the crawl space. It does nothing about the water pressing against the foundation, soaking the soil under the piers, or seeping through the block. Pumps also fail during the exact storms that overwhelm them, and they run up your power bill in the meantime. Interior drainage has its place, usually on lots where the exterior cannot be reached. But if you can keep the water from arriving in the first place, you have solved the problem instead of managing it.
Downspout extensions and underground discharge. Getting roof water ten or more feet from the foundation, or piping it underground to a pop-up emitter or daylight, is the highest return fix in drainage. It is often a few hundred dollars per downspout. See our page on downspout drainage.
Regrading. Restoring a positive slope of about six inches over the first ten feet away from the house. Sometimes this is a day of work with a skid steer and some fill.
A French drain along the wet side. A perforated pipe in a gravel trench, wrapped in fabric, placed at footing depth on the side of the house that takes water, and run to daylight or a dry well. This intercepts groundwater before it reaches the crawl space. A properly built residential French drain in Chattanooga typically runs $2,000 to $4,500 depending on length and how far the water has to travel. Our French drain installation page explains what a correct build looks like.
A curtain drain uphill. On sloped lots, a shallow interceptor trench across the slope above the house catches sheet flow before it ever reaches the foundation. This is the fix that most often gets skipped and most often ends the problem.
If the exterior fixes are done and the crawl space still takes water during the worst storms, or if the house sits so close to a property line or a slab that the exterior cannot be trenched, then an interior perimeter drain and pump is the right next step. At that point it is doing the job it was designed for instead of substituting for a yard that was never fixed.
We will walk the lot with you during or right after a rain if we can, because watching where the water actually goes beats guessing. Call (423) 497-3591 for a free on-site assessment, or read more about whole-yard drainage.
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