You don’t have to be a geophysicist to know that puddles in the basement or a lake on the front lawn are signs of drainage problems.
But many drainage problems aren’t so obvious. Here’s how the pros read some of the more subtle signs of bad drainage, and why you’ll save big bucks if you tackle these problems now instead of later.
Sign #1: Gushing Gutters
A mini Niagara over the edge of your gutter means dead leaves and debris are blocking the flow. But you don’t need a live gusher to tell you you’ve got problems: Vertical streaks of dirt on the outside of gutters, mud spattered on siding, or paint peeling off the house in vertical strips are other sure signs. If you don’t take action, overflowing gutters can rot siding, ruin paint jobs, and cause structural damage.
Best case: Leaves are clogging the downspout, and you just need to clear them out or hire a pro to do it (about $75).
Worst case: Gutters are undersized or improperly pitched and need to be replaced or reinstalled. That could run a few thousand dollars, but it’s still cheaper than new siding.
Sign #2: Downspouts That Dump
Each inch of rain that falls on 1,000 square feet of a roof produces more than 600 gallons of runoff—enough to fill 10 bathtubs to the brim. Dumping that much water too close to the foundation can send it right into the basement, where it can ruin furnishings, flooring, and all the stuff you swore you’d put on shelves one day.
Best case: You can add gutter extensions (about $10 for a 10-foot length) to carry the water at least 5 feet away from the house.
Worst case: Too-short downspouts continually dump buckets of water around your foundation. The water seeps deep into the soil and puts pressure on your foundation walls, eventually cracking them. A foundation contractor comes out and gives you an estimate of $30,000 to excavate around your foundation and fix everything. You begin to cry, dumping buckets of water into the soil around your foundation.
Sign #3: Water Stains in the Basement
Depending on where a stain shows up, you can tell if the problem is caused by surface water, which can be easy to deal with, or water traveling underground, a potentially bigger headache.
Best case: You see stains high on your foundation wall, meaning that water is coming from an overflowing gutter, or that surface runoff backed up against your house because the soil around your foundation doesn’t slope adequately (6 inches for every 10 horizontal feet is best).
Worst case: The stain extends in a line around the basement. If that’s the case, you may be looking at a high-water mark caused by a fluctuating water table. Or, your basement floor lies below the level of municipal storm drains that back up during heavy rains. In either case, an interior drain system and sump pump (around $3,000) will pump any seepage out of our basement, keeping your old bowling trophies dry.
Sign #4: Cracks in the Foundation
Foundations often have small cracks that appear as houses settle over time. Most are harmless, but bigger cracks bear watching. Keep an eagle eye on cracks larger than 1/8-inch wide by marking the ends with an erasable pencil line. Measure the width and jot it down. If you notice the cracks are growing, you’ve got potential problems.
Best case: A crack appears where the builders finished installing one load of concrete and began pouring the next. Such cracks usually don’t penetrate all the way through. And even if they do, as long as they’re stable you can patch them with hydraulic cement or polyurethane caulk for less than $20.
Worst case: Cracks are continuing to widen, indicating that a drainage problem may be ruining the foundation. Call a structural engineer (not a contractor or waterproofing expert) to diagnose the problem, assess the risk, and suggest a repair. Expect to shell out $300 for a structural engineer’s diagnosis.
Sign #5: Flaking and Deposits on Walls
If you see areas of white or gray crust on the basement walls, that’s efflorescence—mineral deposits left behind by evaporating water. Or the wall may be flaking off in big patches, a condition called spalling.
Best case: The efflorescence points to a place where moisture is condensing. It doesn’t cause structural problems, but you may want to check out your gutters, downspouts, and the grading of the soils around your foundation. Scrape off the crust if it looks ugly.
Worst case: The wall is spalling because water is getting inside the masonry. Spalling can be just superficial, but if it’s deeper than ½-inch and widespread, it may be a sign of improper drainage that threatens the integrity of your foundation.
Sign #6: Mildew in the Attic
Sure, the attic might be a strange place to look for drainage problems, but mildew on the underside of the roof can be a tipoff to serious trouble at the ground level.
Best case: Bathroom fans are spewing hot air directly into the attic, where it condenses on the cold back side of the roof and causes mildew. Venting the fan through an outside wall or the roof (about $200) solves the problem.
Worst case: Moisture from the basement or crawl space is rising through the house and condensing on the underside of the roof. In that case, you’ve got to find and stop the source of the dampness under the house. If you don’t act, you’ll end up replacing roof sheathing and shingles, a job that runs $6,000 to $9,000 for the typical house.
Sign #7: Migrating Mulch
When soil doesn’t drain properly, rain runs off in sheets, carving gulleys in the landscape, dumping silt on pathways, and carrying piles of mulch or wood chips where they don’t belong.
Best case: For a few hundred dollars, you can hire a landscaper to create a simple berm (a soil mound) or swale (a wide, shallow ditch) to redirect the water flow away from the house.
Worst case: Your concrete patio cracks and paving stones start popping up because the gravel or sand base material has washed away. After redirecting the water, you’ll need to excavate the patio and start again.
is the author of 10 books about home improvement. She writes a weekly column about home care for the Washington Post.