Basement Moisture: Everything Homeowners Need to Know
Part 3: How Does My Yard and Roof Affect My Basement?
Welcome back for Part 3 of our Basement Moisture series! Here we talk about how ground drainage, including water that runs off of your roof, affects basement moisture.
Ground drainage is the most likely culprit of a home’s basement and foundation moisture issues. The great thing about it being the most likely culprit is many times it’s also a relatively easy fix. Two main surface items heavily impact the amount of moisture around your house: surface grading and gutters and downspouts.
Surface Grading
The surface grade, the slope and slope direction of the ground, around your home is extremely important. The ground near the home should slope down and away from the foundation, it should drop a minimum of 6 inches over 10 feet. Many, many homes just do not have this for many reasons, and many homes may have started with a healthy slope but over time have leveled out or even began sloping toward the structure.
The ground near the home should slope down and away from the foundation, it should drop 6 inches minimum over 10 feet. Additionally, the gutters in the image end too close to the house.
While the optimum is a slope down and away from the home, level is not great, and sloping toward the foundation is extremely bad as it also allows additional water to accumulate and pool at the base of the home. When back filling soil near the base of the foundation, you must be cautious about the force used to tamp and compact the soil into place. Over application of force can damage the foundation. This can lead to a common occurrence of the soil near the foundation naturally settling at a lower level over time. This is a reason why it’s not recommended to abut a sidewalk against the foundation. Sidewalks placed against a foundation tend to compress the soil near the foundation wall and slope toward the house. It creates a nice clean 36 inch wide water catch that drains directly against the foundation wall.
Gutters and Downspouts
The average roof size in the U.S is 1,700 square feet, according to Census data. An average roof sheds about 1,000 gallons of water per inch of rainfall. You do not want this water draining around the foundation of your home.
Unfortunately, it is still extremely common to see downspouts terminate at the base of a home’s foundation. You may see a splash block, which can help prevent eroding the soil under the downspout. But it does not help move water away from the foundation in any significant way. Your downspout discharge should be at least 6 feet away from the foundation, I would even take it a step further and recommend 10 feet. If your yard grading is flat (or even worse sloping toward the home), then discharge the water even further away. Taking the water and discharging down a slope or to a catch basin to be moved away from the home is even better.
Your downspout discharge should be at least 6 feet away from the foundation. I would even take it a step further and recommend 10 feet.
Additionally, a twice yearly gutter cleaning ensures the roof runoff flows free of obstructions. Clogged gutters will overflow the sides dumping rain water on your foundation. They also can act as breeding pits for pests such as mosquitoes.
Moving water from an upper roof to a lower roof
Do yourself a favor: if your upper roof downspout is discharging directly on the shingles of a lower roof, run an extension to the lower gutter. Water from the upper roof will wear and degrade the shingles where it is discharged leading to water intrusion. The downspout should be connected to another segment of gutter that discharges directly into the lower gutter. An upper roof gutter discharging onto a lower roof is extremely common and current building practices allow it, but your future self will thank you if you connect the upper roof downspout to the lower gutter.