Negative Grading: What It Means on Your Home Inspection Report

Your inspector found ground next to the house that slopes toward the foundation instead of away from it, in at least one spot. That's all "negative grading" means: rain that lands near the house, or comes off the roof, runs toward the foundation and soaks in against it instead of draining away.

It may not be how the house was built. The Building Science Corporation (BSC) notes that backfill against a foundation that wasn't compacted well settles over time and leaves a negative slope, and utility trenches leading to the house can sink the same way.

Why It Matters

"Because no waterproofing system is 100% foolproof," the Department of Energy's Building America Solution Center says, the best defense is to keep water from saturating the soil around the foundation at all. BSC says many foundation water problems start with drainage above ground, that this is the first place to look, and that fixing a wet foundation without first fixing surface drainage "might be futile." Water held against a foundation wall builds pressure that pushes it through any joint or crack.

The results range from a damp basement or crawl space, where mold follows (the EPA lists ground that slopes away from the foundation among its basic mold-prevention steps), to soil movement: HUD's Residential Rehabilitation Inspection Guide lists soil swelling from inadequate surface drainage, and erosion around footings from poor surface drainage, among the causes of foundation settlement.

What to Do Before Closing

• Ask where, and what was inside. Ask the inspector to point out each low spot and whether there were signs of water on that side of the basement or crawl space: stains, damp walls, a musty smell, or white mineral deposits (see efflorescence).
• If there are signs of water inside, have a drainage or waterproofing contractor evaluate it, and a licensed structural engineer if there are also horizontal, displaced, growing, or wide foundation cracks, or a wall that bows.
• Talk to your real estate agent about asking the seller to repair or credit it within your inspection contingency. A few low spots are usually a small fix; a lot that slopes toward the house from uphill, or a sunken patio, is a bigger one.

What to Do After You Move In

Regrade so the ground falls away on every side. The Solution Center's minimum, from ENERGY STAR's new-homes requirements, is half an inch of drop per foot for the first 10 feet out, about 5 inches in all. EPA's moisture-control guidance calls for a bit more, a 5 percent slope, or 6 inches over 10 feet, so aim for 6 inches where you can and never less than 5. Hard surfaces next to the house, such as patios and walks, should slope away too.

Where a property line, a neighboring house, or a wall leaves less than 10 feet, the Solution Center says to install a swale (a shallow, graded channel) or a drain designed to carry water away instead. That, a sunken patio, or an uphill slope is work for a landscape or drainage contractor. Fix the downspouts at the same time, since one that empties at the foundation undoes good grading, and keep the gutters clean (our ground-level gutter guide shows how).

Can You Fix It Yourself?

Often, yes, for low spots and sunken beds along the foundation. The rules:

1. Contact 811 first. The Common Ground Alliance says to call 811 or use your state 811 center's website a few business days before any digging, even planting, and to wait until every utility has responded. Many lines are buried just a few inches down.
2. Keep soil below the siding and away from wood. Never pile soil against siding, trim, or wood framing. EPA's moisture guide designs for at least 8 inches of exposed foundation above the finished grade, and the Solution Center lists siding that touches the ground, and yards that slope toward the house, among the obvious causes of water-damaged siding and trim. If you can't get the slope without burying the siding, you need a swale, not more soil.
3. Use the right fill and pack it. The Solution Center's method caps the grade with 2 to 4 inches of silty clay and compacts it so it won't settle; loose fill sinks and recreates the problem.
4. Check your slope. Run a string from a stake at the house to a stake 10 feet out, level it with a line level, and measure down to the soil at each stake. The soil at the far stake should be at least 5 inches lower, and 6 is better.

Frequently Asked Questions

How much should the ground slope away from the house?

At least half an inch per foot for the first 10 feet (about 5 inches), per the Building America Solution Center; 6 inches, EPA's figure, is better. Where you don't have 10 feet, use a swale or drain.

Will regrading fix a wet basement?

It's the first step, along with the downspouts. BSC says many problem cases can be solved with grading and surface drainage, and the City of Mequon, Wisconsin's foundation repair standards start wet-wall repairs the same way: extend the downspouts and increase the slope away from the house. If water still gets in after that, a waterproofing contractor can look at drains below ground and a sump pump.

Is negative grading a deal breaker?

Usually not by itself. What matters is whether water has already caused damage: damp walls, stains, cracks, or a wall that bows deserve a closer look before your contingency ends.

The Bottom Line

Negative grading sends rain at your foundation, and wet soil there is where many basement water problems start. Before closing, find out whether water is already getting in, and talk to your agent about a repair or credit. After you move in, regrade to at least half an inch per foot for 10 feet (6 inches over 10 feet is better), keep soil below the siding, call 811 before you dig, and fix the downspouts too. See more findings in our inspection report decoder.

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