- Each inch of rain on 1,000 square feet of roof produces roughly 620 gallons of water.
- Splash blocks often leave that water within a few feet of the foundation.
- Underground downspout lines should use solid pipe, not perforated.
- Clean gutters matter: a clogged gutter overflows right at the foundation.
Before anyone spends money on French drains or regrading, we look at the gutters and downspouts. On a large share of the drainage calls we take, the main source of water against the house is coming off the roof, and fixing it costs far less than any other drainage work.
The math on roof water
One inch of rain falling on 1,000 square feet of roof produces about 620 gallons of water. A home with a 2,000-square-foot roof footprint sheds more than 1,200 gallons in a single one-inch storm. Northeast Georgia averages roughly 50 inches of rain or more a year, with frequent summer storms that drop an inch or more in an hour.
Now picture all of that water leaving through six or eight downspouts, each emptying onto a small splash block a foot or two from the foundation. That's where crawl space moisture, foundation staining, washed-out beds, and soggy spots along the house come from.
Signs your downspouts are causing problems
- Erosion holes or bare spots at the base of downspouts
- Mulch or pine straw washed away from beds near the house
- Water stains or efflorescence (white mineral deposits) on block or brick foundations
- A damp or musty crawl space, especially after storms
- Splash marks of red clay on siding
- Gutters overflowing at corners during heavy rain
Fix #1: Clean and size the gutters
A clogged gutter overflows along its whole length, dumping water directly beside the foundation where no downspout fix can help. Gutters under oak, pine, and hickory canopy, common on lots from Toccoa to Clarkesville, can clog more than once a year. Gutter guards help. On larger roofs, undersized gutters or too few downspouts can overflow even when clean.
Fix #2: Extend the discharge
The simplest improvement is getting water farther from the house. Above-ground extensions work but get stepped on, mowed over, and kicked loose. For a permanent solution, we run underground lines.
Fix #3: Underground downspout lines, done right
An underground downspout drain carries roof water through buried pipe to a discharge point well away from the house. The details matter:
- Solid pipe, not perforated. Perforated pipe leaks roof water back into the soil right next to the foundation, the exact place you're trying to keep dry.
- Continuous slope. Low spots in the line hold water and sediment and eventually clog.
- A real outlet. Water discharges through a pop-up emitter in the lawn, at a daylight outlet on a slope, into a dry creek bed, or into a rain garden.
- Cleanout access. Leaves and shingle grit get into these lines. A way to flush them extends their life.
- Keep roof water separate. Roof water lines generally shouldn't feed into a French drain meant for groundwater. Mixing them can overwhelm the drain.
Where should the water go?
Ten feet from the foundation is a common minimum target, and farther is better when the yard allows it. The discharge point should be downhill, away from the house, and not aimed at a neighbor's property. On sloped lots, we often bring several downspouts together into one larger line to a single outlet, sometimes finished as a dry creek bed so the water becomes part of the landscape.
The pest connection
Moisture at the foundation is one of the conditions subterranean termites need, and wet crawl spaces bring in crickets, roaches, and silverfish. Our family's pest control company, Hanco Exterminating, sees this every week. Moving roof water away from the house is one of the simplest pest prevention steps a homeowner can take.
When downspouts aren't enough
If water still collects after roof water is handled, the issue is grade or groundwater. That's when regrading, swales, or French drains come in. Our guide to choosing the right drainage fix explains the options.