Site Drainage: The Prep Work That Decides If Your Basement Floods
A basement floods because water reaches it. The water reaches it because the site drainage didn't move it somewhere else. Three layers of protection work together — and most basement problems are one of these three layers missing.
Layer 1: Grading
The grade — the slope of the ground around the house — should fall away from the foundation. The IRC recommends 6 inches of fall in the first 10 feet. Negative grade (water sloping toward the house) is the leading cause of foundation moisture issues.
Check yours: stand at the corner of the house and look at the soil line. Is the ground higher near the house than 10 feet out? If not, you've got a grading issue.
Layer 2: Gutters and downspouts
Gutters catch roof water. Downspouts move it to a discharge point. The discharge point matters: water should leave the downspout at least 5 feet from the foundation, and ideally onto a graded surface that carries it further away.
Splash blocks help. Underground extensions that carry water to daylight or to a dry well help more.
Layer 3: Foundation drains
Around the perimeter of the foundation footing, perforated drain tile (typically 4-inch corrugated or PVC) collects water that reaches the foundation despite layers 1 and 2. It carries that water to a sump pump (interior) or to daylight (exterior).
Many homes don't have foundation drains. Many that do have them clogged with silt and roots after 20-30 years.
What this means for you
Walk your yard after a heavy rain. Where does the water go? If it's pooling near the foundation, layer 1 needs work. If gutters are overflowing, layer 2 needs work. If both look fine and you still get basement moisture, layer 3 is the diagnosis.
What contractors should know
Most flooding issues are layer 1 or 2. Drain tile is the expensive last resort. Solving the cheaper layers first earns the trust to tackle the deeper work when needed.
The part nobody can see later
Most of what decides how this holds up gets covered before the job is over. Once it is closed in, the only record of how it went in is the photos taken while it was still open.
Supervisr's Excavation and Site Preparation QA model works from common industry practice and the installation instructions that ship with the materials. It can review site preparation photos for trench shoring and sloping compliance, soil classification, utility marking, erosion and sediment control, and grading away from foundations. Upload photos of trench sloping/benching angles, shoring or trench box use, utility locate flags present, silt fence and BMPs, foundation grade, and you'll get a documented evaluation back in minutes.
For a homeowner, that record is a straightforward way to understand what you paid for. For a contractor, it is the milestone documentation that stands behind a workmanship warranty years later, long after the crew has moved on to the next job.
About Supervisr
Supervisr is an AI quality-assurance platform for site preparation and excavation work. It works from common industry practice and manufacturer installation instructions, and evaluates site work photos for trench safety, utility protection, and drainage details.
Contractors use Supervisr to document quality at each milestone — backing up a workmanship warranty and building a track record of work they can point to. Homeowners end up with a clear record of what went into their home. See how it works at supervisrapp.com.