The constraint is height, not room
People plan grading in plan view and the failure happens in section. You have ten feet from the wall to the fence, which sounds like plenty, but the fence line and the neighbouring ground are at a level you cannot change, and the soil at the wall can only be raised so far before it reaches the siding. The fall available is the difference between those two fixed heights, and it is often three inches where you wanted six.
Once you look at it that way there are only four moves. Raise the ground at the wall, which spends clearance you may not have. Cut the ground down at the far end, which is limited by whatever is out there at a fixed level. Get the water sideways into a swale before it runs out of fall, which trades a slope for a channel. Or intercept it below ground, which is the french drain route and a different order of expense.
Reading the numbers
The target fall is entered as inches over a distance because that is how grading requirements are usually expressed, and it is converted to a slope so it can be compared with what you have. Six inches over ten feet is 0.6 inches per foot, which is five percent. Two percent is a quarter inch per foot. One percent is an eighth. Those three conversions cover most of what gets discussed on a site.
| Slope | Per foot | Over 10 ft | Ratio |
|---|---|---|---|
| 5% | 0.60" | 6" | 1 in 20 |
| 3% | 0.36" | 3-5/8" | 1 in 33 |
| 2% | 0.24" | 2-3/8" | 1 in 50 |
| 1% | 0.12" | 1-1/4" | 1 in 100 |
What slope your situation requires is not on this table and is not stated anywhere on this page, because grading requirements at a building are set by local codes and ordinances and they differ. Enter what you have been told to achieve, or what you have decided to aim for, and the page tells you whether the ground can deliver it.
Where the swale comes in
A swale is a shallow, wide, grassed channel that runs across the fall rather than down it. It exists because you can always get water to move sideways with very little slope even when you cannot get it to keep moving away from the building. Two feet of bottom width, six inches deep, with four-to-one sides is a section a mower crosses without noticing, and it holds a cross-section of 2.0 square feet, which is a great deal more conveyance than the surface it replaced.
Two things sink swales. The first is no fall along the length, which turns it into a linear pond that stays wet and kills the grass, and half a percent is about the flattest that survives turf and settlement. The second is having nowhere to discharge. A swale is a conveyance, not a disposal, and it has to arrive somewhere the water is allowed to go — which loops back to the same local question that governs everything else on this subject.
Sizing whether a given section carries a given flow is a separate exercise with a separate input, the peak flow arriving, and the culvert and swale flow calculator is built for that. This page gives you the shape, the strip of ground it occupies and the spoil it generates.
Fill settles, and it settles into the shape you were fixing
Grading with delivered soil is not a one-day job that stays done. Loose soil placed against a wall consolidates over the first wet season, and because the fill is deepest at the wall it settles most there. The profile you screeded to a clean five percent becomes a shallow dish with its low point against the foundation, which is the exact defect the work was meant to remove.
The counters are all mundane: place in layers rather than in one lift, compact each one, overbuild the profile so the settled shape is the one you wanted, and go back after the first winter to top it up. It also matters what the soil is. Free-draining sandy fill against a wall carries water down to the footing rather than shedding it across the surface, which is why the surface layer over a graded zone is usually something that sheds rather than something that drinks.
Digging, and where the water ends up
Before digging anywhere on the property, have the underground utilities located. In much of North America that is a free call-before-you-dig service and using it is a legal requirement, not a courtesy. Separately: excavating alongside a foundation can undermine it. Soil next to a footing is carrying load, a trench cut beside or below the footing can let that soil move, and the failure does not always show up on the day. This page gives no excavation procedure and none should be inferred from it. Work close to a foundation, below the footing line, or in soil that will not hold a face belongs with a contractor or an engineer who is standing on the site.
Where roof water and site water are allowed to go is set locally and it varies enormously. Discharging onto a neighbouring property, into a street gutter, into a storm sewer, into a sanitary sewer, or into a watercourse may be required, permitted, permitted only with approval, or prohibited outright depending on where you are, and some jurisdictions also set minimum setbacks and grading requirements at the building. None of that is stated on this page as fact, because none of it can be. Your local building department or stormwater authority is the source, and it is worth a phone call before anything is dug, because water arriving on someone else's land is one of the more common ways a drainage project turns into a dispute.
If the reason you are regrading is water showing up indoors, work through the basement water entry organizer first. Regrading is one of the cheaper interventions, but it only addresses one of several causes, and doing it before establishing whether surface water is even the issue is how people spend a weekend and change nothing.
Questions people ask
How much should the ground slope away from a house?
That figure is set by local codes and ordinances and it is not the same everywhere, so this page asks you for it rather than stating one. Enter whatever your building department, your inspector or your own plan calls for and the calculator tells you whether the distance and height you actually have can deliver it. What is universal is only the direction: water at the surface should be leaving the wall, and any part of the perimeter where it is not is worth fixing regardless of what number applies.
What if there is no room to grade away from the wall?
This is the common case on tight lots and it is why the swale section exists. When you cannot keep water moving away from the building for long enough, you turn it sideways: a shallow channel a few feet out, running across the slope with a slight fall along its length, intercepts surface water and carries it to an end. It needs somewhere to discharge to be worth anything. Where even that is impossible, the remaining options are subsurface interception or managing the water at the source with roof discharge, and both cost more.
Can I just add topsoil against the foundation?
Only to the extent the clearance above allows, and often that is less than the fall you need. Soil piled up against siding, sheathing, a sill plate or the weep course of a masonry veneer causes problems that have nothing to do with drainage — it holds moisture against materials that were designed to be above grade and it gives insects a bridge past whatever was meant to stop them. How much clearance your particular wall assembly requires is a question for the building department or whoever built it, not a number to assume.
Does grading fix a wet basement?
It addresses one of several possible causes and it is usually the cheapest to try, which is why it gets recommended so freely. It does nothing for a high water table, a failed footing drain, a plumbing leak or condensation. Establishing what the pattern actually points at before spending on earthworks is the sensible order, and a persistent problem in a finished basement is worth having someone look at on site rather than working through interventions by elimination.
How much soil will regrading take?
The wedge figure on this page gives the geometry: half the distance times the height shortfall times the length of wall, which for a ten foot strip along forty feet of wall making up three inches of shortfall comes to 50 cubic feet, or about two cubic yards. Order more than the geometry says. Delivered soil is measured loose and placed compacted, the difference is substantial, and settlement over the first season will take more again. Whether you are buying fill or moving what you have depends on whether you are raising at the wall or cutting at the far end.