Downspouts, Loess Soil and a Dry Basement

City of Omaha stormwater materials put it plainly: a 1 inch rain on 1,000 square feet of roof sends more than 600 gallons off the edge. Most houses have far more roof than that, and the gutters gather it into a handful of downspouts. Each outlet is a concentrated stream aimed at the ground beside your house.

Omaha averages about 31.7 inches of rain and melted snow a year, and May is the wettest month, with August and June close behind. A strong summer thunderstorm can drop a lot of that in a short burst. If the downspout ends at a splash block against the wall, the water has nowhere to go but down along the foundation.

Much of the Omaha area sits on loess, a fine silt blown out of the Missouri River valley after the last glaciers. In the Loess Hills across the river it is often more than 90 feet deep. Dry loess stands up surprisingly well. Soaked loess softens, washes out and settles.

Around a basement, the soil that matters most is the backfill, the ring of dirt pushed back after the foundation walls were poured. It is looser than the undisturbed ground beyond it, so it keeps settling for years. Many older houses now have a shallow trough along the wall where the grade has sunk, and that trough fills from the downspout first.

From there the sequence is predictable. Water pools against the wall, soaks down through the loose fill and finds the cracks, the form tie holes and the joint where wall meets floor. Dense subsoil below slows drainage further, which keeps that water parked against the concrete longer.

Nebraska Extension guidance says downspouts should discharge at least 5 feet from the foundation. The same guide recommends grading landscaped soil about 2 percent away from the house, roughly a quarter inch of fall per foot. Those two numbers do most of the work of keeping a basement dry.

Treat 5 feet as the minimum. If the yard is flat or tips back toward the house, carry the water farther, to a spot where the ground clearly runs away. On a walkout lot, aim discharge downhill and away from the lower patio door and the window wells.

• Set a level or a straight board on the ground at each downspout and look for back slope.
• Fill low spots against the wall with packed soil, not mulch or loose gravel.
• Keep finished grade several inches below the siding so it does not hold moisture against wood.
• Recheck after the first wet spring, because new fill settles too.

There are four common ways to get roof water from the downspout to a safe spot. The right one depends on how far you need to go and what stands in the way, such as a driveway, a patio or a planting bed.

On most houses the answer is a mix. Hinged downspout extensions work along the sides of the house, and a buried line handles the downspout that lands beside a driveway or a patio slab.

An underground line has to fall the whole way to its outlet, with no dips where grit and water can sit. Smooth-wall solid PVC holds its slope and can be flushed with a hose. Thin corrugated pipe is cheaper, but it sags between supports, traps grit and seed fluff in its ribs and is hard to clean.

The line should end at daylight on a slope or at a pop-up emitter in open lawn, with a cleanout near the downspout so a clog can be reached without digging. Our page on underground drain lines covers routing, outlets and cleanouts in more detail.

Before anyone digs, call 811 and wait for the utility lines to be marked. A shovel through a gas line or a buried fiber cable turns a drainage project into an emergency, and the trench for a downspout line often crosses right where those services enter the house.

It can be tempting to run a downspout into a floor drain, a sewer cleanout or an old clay pipe that seems to lead somewhere. Do not. Roof water belongs on the surface or in a dedicated storm system, never in the sanitary sewer, and local rules across the metro generally prohibit the connection. If you find an old tie-in, ask your city how to disconnect it.

In Omaha the stakes go beyond a code problem. The older core of the city is served by a combined sewer system covering about 43 square miles, with roughly 800 miles of pipe that carry sewage and stormwater together. In heavy rain those shared pipes can overload and push water back into basements, and every downspout piped into them adds to the load.

If you live in an older neighborhood and have had a sewer backup, ask a plumber about a backflow valve. The city has helped homeowners pay for them through a cost-share program. Keeping roof water out of the pipes is the part you control from the yard.

Grading and extensions only help if water reaches the downspout in the first place. A clogged gutter spills over its front edge and drops a curtain of water right along the foundation, skipping everything you set up below. Nebraska Extension recommends cleaning gutters and downspouts twice a year, and under cottonwoods and maples the spring clean matters most, as our cottonwood season guide explains.

Placement matters too. A downspout that lands at an inside corner beside a window well is a problem no extension fully solves. Sometimes the better repair is moving the outlet or adding a downspout at the other end of the run, so each pipe carries less water and lands somewhere better.

If you are not sure where your roof water ends up, call us. A gutter inspection follows each downspout from outlet to discharge and notes grade, clogs and placement.

The fastest diagnosis there is costs nothing: put on a raincoat and walk around the house during a steady rain. Then look again an hour after it stops.

• Water pouring over the gutter face points to a clog or poor pitch.
• A downspout that only trickles in a downpour likely has a packed elbow, a job for downspout unclogging.
• Every extension should be down and pointing away from the house.
• Puddles within a few feet of the wall after the rain mean the grade needs work.
• Damp spots or white mineral deposits on basement walls near a downspout show where water is getting in.