Grading Your Yard Away From the Foundation

How much should the ground slope away from a house?

The residential code puts a number on it. Section R401.3 of the Montana Residential Code, as published for both the 2021 and 2024 editions, says lots shall be graded to drain surface water away from foundation walls, and that the grade shall fall not fewer than 6 inches within the first 10 feet. That works out to half an inch of drop for every foot you walk away from the wall. Montana's Department of Labor & Industry lists the 2024 International Residential Code as the adopted edition, effective September 26, 2026, so check with your building department if you are pulling a permit for new work.

Hard surfaces get their own rule. The same section says impervious surfaces within 10 feet of the foundation shall be sloped not less than 2 percent away from the building, which covers patios, walks and the part of a driveway that meets the house. The federal Building America Solution Center, run for the Department of Energy by Pacific Northwest National Laboratory, uses the same half inch per foot for 10 feet as its target for soil and lawn next to a home. Six inches sounds small. Over a wall that is 40 or 50 feet long, it is the difference between water that leaves and water that sits.

Why does the ground next to a house sink over time?

Because the soil there was dug out and put back. When a foundation is built, the excavation around it is backfilled, and loose backfill keeps settling for years. The Building America guide tells builders to mechanically compact backfill to prevent later settling, or to schedule a return visit to regrade after the first wet season, which tells you how normal settling is. If nobody ever came back, the strip of soil along the wall may have dropped, and the lawn beyond it can end up higher than the ground at the foundation.

The other common cause is us, meaning homeowners and landscapers. Beds get topped up with soil and mulch every few springs until they are mounded against the siding. A paver patio gets laid flat or slightly toward the house because that is where the door is. A sidewalk heaves in a cold winter and tips back. Any of these can reverse the grade on one side of the house while the other three sides are fine, which is why a drainage complaint is usually about one corner, not the whole building.

How can I check the grade in my own yard?

You need two stakes, a string, a line level or a long carpenter's level, and a tape. Drive one stake against the foundation and another about 10 feet straight out. Tie the string to both and slide it until the level says it is flat. Now measure from the string down to the ground at each stake. If the ground at the outer stake is roughly 6 inches lower than at the wall, you have the slope the code describes. If the numbers are close to equal, or the wall end is lower, that side of the house is collecting water instead of shedding it.

Repeat it every 10 or 15 feet around the house, and pay special attention to inside corners, the ends of downspouts, and anywhere a patio, walk or driveway meets the wall. Take photos of the string and tape. Having the numbers written down makes it far easier to plan a fix or compare quotes. Doing it after a rain or during a thaw is even better, because you can see where water is actually standing.

What soil should go against the foundation?

Something that sheds water rather than soaking it up. The Building America guide recommends capping the top of the regraded backfill with 2 to 4 inches of silty clay and compacting it, so rain and melt run across the surface instead of sinking into loose fill right at the wall. Bark mulch, loose topsoil and gravel do the opposite. They are fine farther out, but a thick fluffy layer piled against the wall is a sponge.

Watch the siding too. Building up soil until it touches siding traps moisture against wood and gives insects a bridge. The same federal guidance describes keeping 8 to 16 inches of foundation wall exposed between grade and the first course of siding in its grade-level drainage design. On many older houses there is far less than that, so a regrade often means taking soil away from the wall and pushing the high point out into the yard, not adding fill.

What if there isn't 10 feet to slope away?

The code anticipates it. R401.3 includes an exception: where lot lines, walls, slopes or other physical barriers prohibit 6 inches of fall within 10 feet, drains or swales shall be constructed to ensure drainage away from the structure. In practice that is the side yard between two houses, a driveway that runs right along the wall, or a hillside lot where the uphill side of the house faces a bank.

A swale is a shallow, planted or grassed channel that carries water around the house. The Building America guide calls for side slopes no steeper than 3 to 1 and a fall along the channel of 2 to 4 percent, because flatter channels pond and steeper ones erode. Where there is not even room for a swale, a buried drain does the job; our guide to French drains covers when that is the right call. On a lot where the slope comes down toward the house, the fix is usually to intercept water uphill before it ever reaches the foundation, sometimes with a retaining wall and drainage behind it.

Why does grading matter more in western Montana?

Because our worst water arrives when the ground is frozen. A spring melt dumps a winter's worth of snow onto soil that cannot absorb it, so every drop moves sideways to the lowest point it can find. If the lowest point is your foundation, that is where it goes. Our guide to yard drainage and spring melt walks through how to watch a melt and read where water is going.

Snow storage makes it worse. The Building America guide notes that in cold climates, snowmelt from the roof can fall to the ground and freeze into an ice ridge along the foundation, and that ridge can turn melt water back toward the wall. A plowed or shoveled pile against the house does the same thing in March. Grading the first 10 feet properly, and deciding where to pile snow before the first storm, removes most of the problem.

Where is the water allowed to go?

R401.3 says surface drainage shall be diverted to a storm sewer conveyance or other approved point of collection that does not create a hazard. On most residential lots that means a part of your own yard that is lower and can take the water: a lawn area, a planted bed, a swale or a rain garden. Directing a concentrated flow onto a neighbor's property is the version that starts disputes, so plan the outlet before you plan the slope.

Inside Missoula, the City's Stormwater Utility says most of the city's stormwater goes to the aquifer through more than 6,000 dry wells, and that any discharge not made up entirely of rainfall or snowmelt is illicit. Clean roof and yard water is fine. Water that has picked up fertilizer, oil or wash water is not something to steer into a street inlet. On a lot with no storm system to reach, your own ground has to handle the water, which makes the choice of outlet even more important.

Do I need to call 811 before regrading?

Yes, for anything more than raking. Regrading means cutting into the soil next to the house, which is exactly where gas, power, water and communication lines enter. Montana 811 says you can dig two full business days after you call and get a ticket number, and recommends calling at least three days before you plan to start. Marks are good for 30 days if they are still readable.

811 does not find everything. Montana 811 explains that utilities generally own lines up to the meter, and if the meter is on a pole or pedestal in the yard, the line from there to the house may not be located. Sprinkler lines, landscape lighting cable and wires to a shop are also yours to find. If you have a sprinkler system, know where the lines run before anyone digs along the foundation.

How does regrading fit with patios, beds and sprinklers?

Grading goes first. A patio or walk laid on a bad grade locks the mistake in place, and a bed planted across a drainage path stays wet whatever you plant in it. That is why our landscaping design work starts with where the water goes, then grading, then hardscape, then irrigation and planting. If you are adding a patio against the house, the 2 percent fall away from the wall is part of the design, not an afterthought.

Sprinklers deserve a look too. Spray heads that hit the foundation, or a zone that runs every morning along a north wall that never dries out, keep the soil next to the house wet all summer. Adjusting or replacing those heads is often part of a drainage fix. Our guide to irrigation zone design explains how zones should be laid out so beds next to the house get only what they need.

When should you bring in a professional?

When the fix means moving more than a few wheelbarrows of soil, when the slope has to run around a patio or driveway, or when you are not sure where the water can legally and practically go. Also call someone if you see cracks, bowing walls or water coming through the foundation itself. Those are structural or waterproofing questions for a foundation contractor or engineer, not a landscaper, and grading alone will not fix them.

We handle grading and surface drainage, plus the beds, sod and hardscape that go on top, as part of our landscaping work across Missoula, Lolo, Florence, Stevensville, Corvallis, Victor, Hamilton and Darby. This guide is part of our Montana Landscaping, Lawn & Irrigation Guide. Call (406) 215-7319 or request a free estimate and we will walk the house with you, check the grade on every side, and tell you plainly whether grading will solve it.

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