Nearly every drainage call we take between now and February starts the same way. Somebody has standing water where they never used to, or a damp crawlspace, or a strip of lawn that has turned to mud and stayed that way. And most of the time the thing that caused it is bolted to the corner of the house and has been there since the place was built.
Downspouts. Nobody thinks about them until something goes wrong, and by then the water has been doing the same thing every storm for years.
The number that surprises people
Here is the figure worth carrying around. For every inch of rain that falls, a thousand square feet of roof sheds about 623 gallons of water. That is University of Georgia Extension’s arithmetic, not ours.
So a Dunwoody ranch sitting on a 2,000 square foot footprint is handling roughly 1,250 gallons in a single inch of rain. Atlanta averages close to 50 inches a year, and December is our wettest month at around 5.7 inches. Run that across a winter and you are moving tens of thousands of gallons past your foundation, usually through four or five downspouts, usually onto the same four or five patches of dirt.
Water does not negotiate. It goes where the ground lets it go, every storm, and it has all winter to work at it.
Follow the water on the next wet day
Ask a homeowner where their downspouts discharge and most will say “into the yard.” Ask them to point at it and they usually cannot. So the first job costs nothing and takes ten minutes.
Wait for a proper rain, put a coat on, and walk the outside of the house. At each downspout, look at three things:
- Is the water coming out of the bottom, or out of a seam halfway up?
- Where does it land, and where does it go in the six feet after that?
- Is the ground underneath dug out into a little crater?
That crater is the tell. It means water has been hitting bare soil at speed, and it means the ground right against your foundation has been soaking on every rain for a long time.
The mistake almost everybody makes
The splash block. A concrete or plastic splash block drops the water about eighteen inches from the wall, and eighteen inches is nowhere near far enough. It stops the soil washing out, which is the part people can see, and it does nothing whatever about where the water goes next.
The second most common one: a downspout that somebody extended properly with a four foot length of pipe, and then that pipe got nudged aside so the mower could get past. We find them lying in the flowerbed. It has usually been like that since spring.
What six inches in ten feet looks like on a real lot
The building code has a number for this. Ground around a house should fall at least six inches within the first ten feet, and any paving inside that ten feet should slope at two percent or better (IRC R401.3).
On a flat-looking Dunwoody lot, six inches over ten feet is more fall than most people picture. What we find instead is often the opposite: a walkway poured dead level, or a flowerbed that has been topped up with fresh mulch every spring for a decade until the bed sits higher than the lawn it is meant to drain onto. An inch a year, nobody notices, and then one winter there is water under the house.
If you check one thing this weekend, check whether your beds have grown taller than the grass beside them.
Where the water should go instead
There are three honest answers, and which one is right depends on the yard.
Extend it above ground. Cheapest and easiest to undo. A proper extension carries the water past the backfilled ground around the foundation and out onto something that slopes away. Done well it disappears within a week once the grass grows over the end.
Bury it. A solid pipe, not corrugated and not perforated, running from the downspout out to a pop-up emitter in a lower part of the yard or to daylight on a slope. This is what most people mean when they say French drain, and it is not one. A French drain collects water out of the ground. A downspout line carries roof water somewhere else. Build one as though it were the other and you get a pipe full of silt inside two years.
Put it to work. If the landing area is far enough from the house and the ground will take it, a rain garden turns the problem into a planting bed. UGA Extension sizes them to handle an area five to ten times bigger than the garden itself, dug six to eight inches deep. It is the one answer that makes roof water an asset instead of a nuisance: less going into the storm system, more going into the ground, and a bed that does not need watering through July.
Georgia clay changes the plan
Now the local part. Our soil is red clay, and clay does not take water quickly. A rain garden that would drain overnight in sandy ground can sit wet for two days here if it has been cut into unamended subsoil.
So we test before anyone digs. Fill a hole with water and time how long it takes to disappear. If the answer is “it was still there the next morning,” the plan changes: more depth of amended soil, or a different discharge point altogether. Anyone who quotes a rain garden off an aerial photo without touching your soil is guessing.
That same clay is why a badly buried downspout line is worse than no line at all. Pipe laid with no fall, in clay, is just a long thin pond alongside your house.
What we would do at our own house in October
October, not January, and for two reasons.
The ground is workable now. Once the winter rain has been going a few weeks, digging in wet clay tears up a lawn in a way that takes until spring to grow out, and a trench backfilled in soggy conditions settles unevenly afterwards.
The leaves are the other reason. Dunwoody has a lot of mature hardwood and pine, and once the gutters pack, water overshoots the gutter entirely and lands in a concentrated line right at the foundation. So: clear the gutters first, then look at the downspouts, then decide whether you have a drainage problem or a housekeeping one. A good number of the yards we get called to look at do not need a pipe at all. They need the gutters cleared and one extension put back where it was. While you are up there, the leaves themselves are worth keeping rather than bagging.
When it is bigger than a downspout
Some of it is not yours to fix. The City of Dunwoody looks after the stormwater pipe network in the public right-of-way and has identified around four miles of pipe there needing rehabilitation. Everything between your roof and that point sits with the property owner.
If the water arriving in your yard is coming from uphill, or off a neighbor’s regraded driveway, or out of a pipe outfall you did not install, that is a different conversation and worth having before you spend anything on your own side of it. We have written more about yard drainage across North Atlanta and about what standing water does if you leave it.
Walk it with us
We are on Dunwoody lots most weeks through the fall, and we are happy to walk yours and tell you which of the three answers fits. There is no charge for the walk, and if the answer is “clean your gutters and move that pipe back,” we will tell you that and leave you to it.
More seasonal pieces like this one are collected in our landscaping guides.
