Regrading a yard to slope away from the house

The slope target: 6 inches in the first 10 feet

The International Residential Code, section R401.3 Drainage, says the grade around a house shall fall a minimum of 6 inches within the first 10 feet from the foundation. That works out to about a 5 percent slope. It is the number building inspectors check on new construction, and it is the standard we regrade to on existing homes.

The code allows for tight lots. Where lot lines, walls, slopes, or other barriers make 6 inches of fall in 10 feet impossible, the grade must still slope away from the foundation at a minimum of 2 percent, and the water has to be directed to drains or swales that carry it away from the house. Impervious surfaces such as walks and patios within 10 feet of the foundation must slope at least 2 percent away from the building.

Many older houses in Rockland and Bergen no longer meet that standard, even if they did when they were built. The backfill around a foundation settles for years after construction, and the result is a shallow dip right along the wall. Mulch beds, pavers set at the wrong pitch, and years of topdressing the lawn can also flatten or reverse the slope.

Siding and foundation clearance

The easy way to get more slope is to pile soil against the house. That creates a new problem. The code, in IRC R317.1, requires wood siding, sheathing, and wall framing to be at least 6 inches above the ground unless it is rot-resistant or pressure-treated wood. The clearance to a concrete step, patio, or other hard surface is 2 inches. Soil against the siding holds moisture against the wall, invites insects, and can hide rot for years.

So the grade has two limits at the wall: it has to be at least 6 inches below the bottom of the siding, and it has to fall away from there. When the existing soil is already close to the siding, raising the grade at the house is not an option. The slope has to be made by lowering the ground farther out instead, cutting the yard down so the high point stays at the foundation and the grade drops toward the lawn.

We measure from the bottom of the siding and from any basement window sills before we plan the grade. Window wells, dryer vents, and hose bibs all set limits on how high the soil can come. Where a basement window sits too low for the grade to work, the window well needs its own drain.

Swales: moving the water after it leaves the house

A slope away from the foundation moves water out 10 feet. After that, the water still has to go somewhere. On most lots it collects between houses, along a fence line, or in a back corner. A swale is a shallow, wide channel shaped into the lawn to carry that water around the house and toward a lower spot, the street, or a wooded edge.

IRC R401.3 requires swales within 10 feet of the foundation to slope at least 2 percent. We keep swales broad and shallow, often 6 to 12 inches deep and several feet wide, so they can be mowed like the rest of the lawn. A steep narrow ditch erodes and is hard to maintain.

On the narrow side yards common in Pearl River, Nanuet, and much of Bergen, the swale usually runs between the two houses toward the street or the back of the lot. The water has to stay on your property until it reaches a legal outlet. In New York and New Jersey a landowner can be held liable for collecting water and sending it onto a neighbor's land, so a regrade that simply tilts the yard toward the neighbor's foundation is not a fix. Our yard drainage guide covers outlets in more detail.

Topsoil vs fill

Regrading usually moves soil more than it adds soil. Where fill is needed to build up low areas away from the house, the bulk of it should be clean fill or subsoil that compacts well. Clay fill is common in this area and works as a base because it sheds water, as long as it is placed in thin layers and compacted.

The top 4 to 6 inches should be screened topsoil, which is what the new lawn will grow in. Using topsoil for the whole fill depth is a mistake. Topsoil is loose and full of organic matter, and it settles and compresses much more than subsoil. A regrade built from 18 inches of topsoil can sink several inches in the first year and put the dip right back against the house.

Near the foundation, the finished surface should be topsoil with a denser layer under it so water runs off the surface instead of soaking straight down next to the wall. We do not use sand or loose stone as a fill against the foundation for surface grading, because it lets water drop straight down beside the basement.

Compaction and settling

Every lift of fill is compacted before the next one goes on. We place fill in layers about 4 to 6 inches thick and run a plate compactor or the tracks of the machine over each one. Soil that is too wet does not compact well and soil that is bone dry does not either, so timing the work around rain matters on clay.

Compaction needs a light touch near the foundation. Heavy equipment right against a basement wall can push on it, so the last few feet next to the house are compacted with a plate compactor or hand tamper. Away from the house, the goal is soil firm enough that it will not settle into dips over the first winter.

The topsoil layer is firmed but not compacted hard, because grass roots need loose soil. The final surface is checked with a laser level along several lines out from the house to confirm the fall. We would rather find a flat spot during grading than after the seed is down.

Seeding and protecting the new grade

Bare soil on a new slope erodes in the first hard rain. The grade needs grass or ground cover on it as soon as possible. Seeding works best from late August through September in this area, and again in spring. Sod can go down in most of the growing season and holds the soil right away, which makes it a good choice for swales and slopes steeper than a gentle lawn grade.

Seed on a slope should be covered with straw or an erosion control blanket so rain does not wash the seed and topsoil into the low end of the yard. Swales often get sod or a blanket even when the rest of the lawn is seeded, because they carry the most water. We handle seeding and sod as part of the same job.

The first few big storms are the test. Walk the yard during a heavy rain and watch where the water goes. A small low spot that shows up in the first season can be topdressed and reseeded. A larger one usually means fill settled and needs to be built back up.

Call 811 before any digging

In New York, 16 NYCRR 753-1.2 defines excavation to include grading and backfilling with mechanized equipment, so machine regrading counts even when it is only a few inches deep. It moves soil where gas, electric, water, cable, and irrigation lines can be buried. Service lines to a house are often shallower than people expect, and grading can cut them or leave them too close to the surface.

In New York, 16 NYCRR Part 753, section 753-3.1, requires notice to the one-call system at least two but not more than 10 working days before excavation starts, not counting the day of the call. The one-call center in New York is 811. In New Jersey, the law requires at least three business days of notice to New Jersey One Call through 811 before excavation.

The markout covers utility-owned lines. Private lines such as a lamp post feed, a line to a detached garage, a sprinkler system, or a propane line are usually not marked, and the owner should tell us where they are. We call in the markout on every grading job and wait for the marks before a machine touches the ground. More on how we handle grading is on our drainage and excavation page.

Questions