Drainage work $1,000 to $3,000Excavation and grading $2 to $8 per sq ftBuilt to the Ottawa grading spec
Driveway excavation and drainage, built to the City's grading numbers
Driveway excavation and grading in Ottawa runs $2 to $8 per sq ft, and correcting a driveway that holds water costs $1,000 to $3,000. Paving Experts Ottawa grades to the City’s numbers, with fall away from the house and a slope no steeper than 6 percent, before any surface goes on.
Driveway grade held to 6 percent maximum, positive from the road edge
Swales never flatter than 1 percent, subdrains where they are under 2
150 mm clearance between foundation and finished grade
Discharge kept off the neighbouring property
Book a drainage assessment
Tell us where the water sits and how long it stays there.
We survey the fall before quoting anything.
6%Maximum driveway grade in Ottawa's minimum grading specification
1%The grade a swale must never fall below
150 mmMinimum clearance between foundation and finished grade
2.4 mDepth the City buries watermains to stay below frost
Excavation exposes clay to frost for the first time
The City of Ottawa’s own geotechnical guidelines identify sensitive marine Champlain Sea clay as vulnerable to frost heaving when previously unexposed to freezing. Excavating is what exposes it to frost for the first time. Clay sitting under a driveway that has not moved in forty years has been insulated from frost the entire time. Dig that driveway out and you have exposed it. If the replacement goes back with a shallow base, no separation and no thought about where meltwater ends up, the new surface can move more than the old one ever did. This is not an argument against excavating. It is the argument for excavating to a depth that actually works, separating soft subgrade from clean stone, and making the granular a drainage layer before it is a structural one. Every hour spent on the grade before the stone goes in is cheaper than the repair that follows getting it wrong.
Where residential drainage usually goes wrong
Almost every drainage failure we are called to look at breaches one of the City's published grading numbers.
A swale cut flat
The specification never allows a swale flatter than 1 percent, and anything under 2 percent needs a rigid perforated subdrain beneath it. A swale cut flat holds water instead of moving it, which is worse than no swale at all because it concentrates the problem in one place.
An apron that fell the wrong way
Roads get resurfaced and the apron does not always get adjusted, so the driveway ends up falling back toward the garage. Grade must run positively from the curb or edge of pavement to the building, and no amount of new asphalt fixes a fall that runs the wrong direction.
Finished grade against the foundation
Forty years of topsoil and mulch creep up the wall until the 150 mm minimum clearance between foundation and finished grade has gone. Water then arrives at the building instead of leaving it, and the driveway gets blamed for it.
The numbers Ottawa publishes, and what they mean for your lot
Driveway grade must not exceed 6 percent
With positive grade running from the curb or edge of pavement toward the garage. Steeper than that and you get scraping, winter traction problems and water that arrives at the building rather than leaving it.
Swales are never flatter than 1 percent
And a swale under 2 percent needs a rigid perforated subdrain beneath it. A flat swale is a pond with ambitions. This is the detail most residential grading work skips entirely.
Grassed areas run 2 to 7 percent unterraced
Above 7 percent the specification calls for terracing at a maximum of 3 to 1. It is worth knowing because the landscaping either carries water away from the driveway or delivers it there.
Discharge must not affect the neighbours
Water leaving at grade cannot be pushed onto the adjacent property. Solving your drainage by moving it next door is not a solution, and it is the fastest way to a dispute you will lose.
Our Process
How we approach a drainage job
1
Shoot the levels
We survey the actual fall from the road edge to the garage and around the foundation rather than eyeballing it. Most drainage problems are a grade problem that was never measured.
2
Find where the water goes now
We trace the route meltwater and roof runoff actually take, look for the low spots that hold it, and check the foundation clearance before deciding what has to move.
3
Excavate and reshape
Dig to real depth, cut the swale or the fall, place subdrain where the grade is flatter than 2 percent, and separate soft clay from clean stone with geotextile.
4
Rebuild the base and prove the fall
Granular goes back in compacted lifts, and we check the finished profile with a level rather than by eye before any surface goes down over it.
The base is a drainage layer before it is a structural one
Granular under a driveway gets described as a base, which makes it sound like its job is holding weight. It does hold weight, but that is the second job. The first job is drainage. Clean, well graded, properly compacted stone has open voids that let water move through and out of the structure rather than sitting in it, and that is how you remove the third condition of frost damage. Once the granular is contaminated with clay fines, or compacted so poorly that it holds moisture, or placed with nowhere for the water to go at the bottom of it, the structure above it is on borrowed time no matter how thick the asphalt is. This is also why geotextile matters so much on soft subgrade. Separation is not a refinement. It is what keeps the drainage layer working as a drainage layer for the life of the driveway.
What excavation and drainage work costs
Ottawa-area ranges. The variables are depth, how much material has to leave the site, and whether the fix is regrading or a new drainage structure.
Site excavation and grading
$2 to $8 per sq ft
Strip, dig to depth and reshape the subgrade
Material hauled off site
Range reflects depth and access
Quoted separately from any surfacing
Drainage is the one frost condition you can control
Frost damage requires three things at the same time: a frost-susceptible soil, sub-freezing temperature and available water. Remove any one of them and the damage is minimised. That framing tells you immediately where the leverage is.
The soil is what it is. Much of this region sits on Champlain Sea clay, a high plasticity clay with a sensitivity between 65 and 85 and a natural water content of 64 percent against a liquid limit of 52 percent. A soil is generally classed as frost-susceptible once 10 percent or more passes the 0.075 mm sieve, and Ottawa's signature clay is comfortably in the worst category. The temperature is fixed too. January mean is minus 10.0 C, and the 1991 to 2020 normals give the city 231.9 cm of snow and 757.2 mm of rain a year.
Which leaves the third condition. Water is the only one of the three a contractor has any control over, which is why drainage comes before everything else. A driveway is not a surface with some stone under it. It is a drainage structure with a surface on top.
Borehole spacing and what a driveway excavation reveals
Where Champlain clay is present, the City requires boreholes to 5 to 6 metres against 4 to 5 metres in competent soils, at infill spacing of 30 to 50 metres.
Think about what that spacing means. A professional geotechnical investigation, on a site the City is going to approve, does not assume that conditions 30 metres away are the same as conditions here. It samples again. If that is the standard for a serious investigation, the observation that your neighbour's driveway has been fine for fifteen years carries very little weight about your lot. The City applies the same logic to its own infrastructure: watermains go in at a minimum of 2.4 metres below grade specifically to stay below the frost line.
We cannot drill boreholes for a driveway and nobody should be charging you as if they had. What we can do is dig, look at what is actually under your property, and tell you what we find before the granular goes back in. Any workmanship warranty is set out in your written quote, job by job. Call (343) 314-8525.
Excavation and drainage questions
What slope should a driveway have?
Ottawa's minimum grading specification for infill lots caps driveway grade at 6 percent, with positive grade running from the curb or edge of pavement up to the garage. That means water leaves toward the road rather than collecting at the building. If the existing fall runs the wrong way, no amount of new asphalt fixes it, and the grade has to be corrected first.
What does driveway drainage work cost in Ottawa?
Drainage correction generally runs $1,000 to $3,000 depending on what has to move. Site excavation and grading in this market runs $2 to $8 per square foot. Those are separate scopes and we itemise them separately, because a quote that folds drainage into a square foot surfacing rate tells you nothing about whether the drainage work is actually in there.
Do I need a swale along my driveway?
If water has nowhere else to go, yes. The specification is specific about them: a swale is never built flatter than 1 percent, and one under 2 percent requires a rigid perforated subdrain beneath it. A swale cut too flat holds water instead of moving it, which is worse than no swale at all because it concentrates the problem.
How deep does a driveway excavation go?
Deep enough to place a real granular section, which is more than deep enough to fit the surface back in. The City's own light duty road section is 150 mm of Granular A over 300 mm of Granular B Type II. A driveway carries far less load than a road, but the granular is doing the same drainage job, and the depth has to be decided from what the subgrade turns out to be rather than from a default.
Can you fix a driveway that floods without rebuilding it?
Sometimes. If the structure is sound and the problem is a low spot or a wrongly directed fall, regrading and a corrected swale can solve it. If the base is saturated, soft underfoot or has already broken up, the water has been in there long enough to do structural damage and patching the surface just hides it. We probe before recommending either.
Find out where your water is actually going
We survey the fall, trace the runoff and quote the grading work on its own line.
