Grading won't fix every wet basement, but it's cheap to check yourself.
How to check your slope in 10 minutes
You need a 4-foot level, a straight board about 10 feet long and a tape measure. Set one end of the board on the ground against the foundation, hold it out level (use the level on top, not the ground, as your reference), and measure from the bottom of the board down to the soil at the 10-foot end. Six inches or more is on target. Less than that, flat ground or ground that rises away from the wall means water has no reason to leave.
Repeat on each side, especially at inside corners, under downspouts and where a patio meets the house. Backfill against a foundation settles over time, so even a house graded right when built can lose its slope.
Watch it rain
A slope reading tells you what the ground should do. A rainstorm shows what it actually does. During or just after a heavy rain, walk the house and photograph the same spots again later that day and the next morning. Note where water collects, which way it runs and whether a damp patch shows up inside the basement at the same time. EPA recommends checking the foundation, the joints where paving meets the building and the slope of walks and patios twice a year and after heavy rain or fast snowmelt.
A contractor can do far more with "the back corner puddles within an hour and the wall behind it gets damp the next day" than with "the yard gets wet." Our guide on documenting basement water before you get quotes shows what else to record.
Tell grading problems apart from other water problems
- Soil that dips toward the wall or a spot that refills after every storm points to grading. This is usually fixed with compacted fill sloped away from the house.
- A patio, walk or driveway tilted toward the house is a different repair. Adding soil elsewhere won't change it; the slab has to be reset, mudjacked, replaced or given a drain.
- Water pouring out at the base of a downspout points to gutters and downspouts. Building America says to send roof water at least 10 feet out, to a swale, drywell or other approved spot. See our guide to gutter guards on tree-heavy lots if clogging is the cause.
- Dampness with no pooling outside can come from plumbing leaks, groundwater or summer condensation. Grading alone won't solve those, and our guide comparing interior drainage and exterior waterproofing covers the next step.
Don't just pile dirt against the wall
Raising the soil against the wall can bury the bottom of siding and trade one moisture problem for another. Ask whoever does the work how much clearance your wall material needs between finished soil and siding before they bring in fill. Building America's guidance calls for compacting the fill so it doesn't settle back into a low spot, and capping it with a few inches of denser soil that sheds water.
On a tight lot or a Philadelphia rowhome yard where there isn't 10 feet to work with, the guidance is a shallow swale (a gentle drainage channel) or a drain that carries water away, not a steeper bump of soil. Make sure the water ends up somewhere it's allowed to go, not on a neighbor's wall.
Philadelphia: help with downspout water
If a downspout dumps next to the foundation, Philadelphia Water Department's Rain Check program installs a free rain barrel for eligible Philadelphia residential properties and a metal downspout planter for $100. The planter holds about 78 gallons and drains back into the sewer pipe, an area drain or a lawn downhill. You have to attend a virtual workshop first; the program's site says workshops resume in January 2027 and barrel installs in March 2027. Rain gardens also count, but Building America advises putting them more than 10 feet from the house. Our guide on Philadelphia stormwater credits and rain gardens covers the bill side.
Who to call and what to ask
For simple low spots, a landscape or grading contractor who does residential drainage is the right call. If space is tight, the yard drains toward the house from a neighbor's lot, or water still comes in after grading, ask for a drainage engineer or a basement-waterproofing specialist instead. Ask any of them:
- What slope will the finished grade have, measured over the first 10 feet?
- How will you compact the fill so it doesn't settle?
- How much clearance will be left between the soil and my siding?
- Where will the water end up, and does that need any approval from the township or city?