Grading, drainage and swales

Drainage is the least visible landscape work and the only kind that prevents a five-figure problem elsewhere in the house. It is also the part with the most rules attached, because water leaving your lot lands on somebody else's.

Step one: understand what you may and may not change. The City of Ottawa's own guide is blunt: you are not allowed to change the grading of a property, water must follow approved drainage patterns and cannot be directed to neighbouring properties, and ditches must not be altered because they slow runoff, filter contaminants and reduce flooding (City of Ottawa Landscaping Education Guide). Most suburban lots were graded to an approved plan at construction, and that plan is the reference. Changing it is a City conversation, and the Site Alteration By-law is the instrument that applies to larger changes.

Step two: measure before you diagnose. A level or a laser on the ground is worth more than an opinion. What matters: the fall away from the foundation over the first two metres, the high and low points of the lot, where the swale between you and your neighbour actually sits, and where every downspout discharges. Photographs during a real rainstorm are the most useful diagnostic available and cost nothing.

Step three: the cheap fixes first. Extend the downspouts so they discharge at least 1.8 m from the foundation onto a surface that carries water away. Restore the fall against the house where flowerbeds and mulch have built up above the correct level over twenty years, which is extremely common in older Ottawa neighbourhoods. Clear the swale of the raised bed, the shed or the fill that somebody added. In a large share of wet basements, that is the whole repair.

Step four: re-grading and swales, done properly. Where a real correction is needed, the approach is to re-establish the design drainage pattern rather than invent a new one: fall away from the building, a swale carrying water along the property line as the original plan intended, and no discharge concentrated at a neighbour's foundation. On clay this needs care, because a swale cut into clay holds water rather than conducting it unless it has fall the whole way.

Step five: subsurface work, where it is justified. A French drain, a catch basin and a buried line, or a dry well can all help, and none of them substitutes for surface grading. Any of them requires a locate through Ontario One Call before digging, which is mandatory, free and needs five business days (Ontario One Call). A buried line has to discharge somewhere legal, and connecting private drainage to the City's system is not a decision to make on site.

How long it takes. Downspout extensions and restoring the fall against the house is a day. A swale rebuild along one property line is two to four days. A full lot re-grade with topsoil and sod is a week to two, and it needs a dry stretch, which in Ottawa means May to June or September to October rather than the middle of a thaw.

What it costs in 2026. Indicative ranges. Downspout extensions and local re-grading against the foundation is commonly $600 to $2,500. A swale rebuild along a property line runs roughly $2,500 to $7,000. A full lot re-grade with imported topsoil and new sod is $6,000 to $20,000, with sod alone at $0.35 to $4 per square foot installed (RenoQuotes 2026). A catch basin with a buried line to a legal outlet is commonly $3,000 to $9,000. What moves the number: how much soil comes in or goes out, machine access, and whether hard surfaces have to be lifted and relaid. Add 13 per cent HST.

What makes Ottawa drainage different. Clay and the spring melt. Much of the city sits on Champlain Sea clay, which drains very slowly (NRC on Leda clay), so surface water sits rather than soaking away. Then the melt: the whole winter's snowpack leaves in about a fortnight, usually in late March, on ground still frozen at depth. That combination is why March and April are the months Ottawa basements leak, and why a grading fault that looks harmless in August matters. Frost is the third factor, with foundation depths reaching as much as 1.2 m below grade in clay soils under the Building Code (OBC 9.12.2.2), which is also the depth below which a buried drainage line stops freezing.

Who should do the work. Landscaping and drainage work is not a licensed trade in Ontario, and only the title Landscape Architect is protected, to full OALA members (OALA on the title). Where the work moves beyond restoring an approved pattern you want somebody prepared to put levels on paper, and for anything involving a retaining structure or a change the City has to approve, a professional engineer, verifiable in the PEO directory. Drainage disputes with a neighbour are a civil matter, and the strongest position in one is a measured survey and a set of dated photographs.