Heavy rain in St. Louis can leave a home's basement and crawl space damp for days, even when the plumbing and sump are working. Much of that water comes from the roof and the ground right beside the house. Downspouts and grading, meaning the slope of the soil around your foundation, decide whether rain moves away from the walls or sits against them. This guide walks through a practical check you can do in an afternoon.
Why the Outside Matters for Indoor Humidity
Moisture that soaks into the soil next to a foundation can push through block, poured concrete, and cracks. Once it reaches the inside, it raises the humidity of basement air and can wet stored boxes, the edges of carpet, and the bottom of wall board. Good drainage outside reduces how much water reaches the wall in the first place, which means any dehumidifier or ventilation in the home has less work to do.
Check the Downspouts
- Follow each downspout from the gutter to the ground. Look for gaps at joints, sagging sections, and leaks at the seams.
- Confirm that the bottom of every downspout discharges well away from the foundation, onto ground that slopes away from the house.
- Look for an elbow or a short pipe that dumps water right at the wall. These often end up pointing back at the house after a storm pushes them out of line.
- Check whether a downspout connects to a buried line. If it does, make sure the outlet is clear and not blocked by leaves, silt, or soil.
Check the Grade
Stand at each corner of the house and look at how the ground runs. It should fall away from the foundation. Soil that slopes toward the wall, or that has settled into a shallow dip beside the foundation, will collect water after every heavy rain. Mulch beds, patio slabs, and raised planters can also trap water against the wall if they sit higher than the soil beside them.
Pay attention to spots where water pools after a storm. A wet patch that lingers for a day or longer is a clear sign the surface needs work, especially in the low corners common to many older St. Louis lots.
Inspect the Area During and After Rain
A useful time to check is during or just after a steady rain. Watch where the water goes. Note whether it runs toward the house, collects at the base of a wall, or flows away on its own. Take photos, since they help if you later talk with a contractor or your insurer. Also note where dampness shows up indoors afterward, such as a basement corner or a crawl space wall.
Simple Fixes Homeowners Can Make
- Extend downspout outlets with rigid or flexible extensions so water lands farther from the wall.
- Clear leaves and debris from gutters and downspout openings before the rainy season starts.
- Fill low spots in the soil next to the foundation with compacted fill, then slope the surface away from the house.
- Pull mulch and soil back from the base of the wall so the siding or foundation stays visible and can drain.
- Move planters and temporary water features away from the foundation.
When to Bring in a Professional
Some issues go beyond a weekend project. Consider calling a qualified person if water keeps entering after the surface has been graded, if a downspout connects to a buried line you cannot trace, if the foundation shows new cracks or a bowed wall, or if the drainage route runs under a driveway or patio. A licensed contractor or home inspector who works on St. Louis homes can look at the full drainage picture. Ask them to explain what they found and why it matters for your house.
Keep a Simple Log
Write down the date of each heavy rain and what you noticed afterward. Over several storms, a log shows patterns, such as a corner that stays damp or a downspout that overflows. That record helps you decide whether a fix is working, and it gives you clear notes if you need to ask for help later.