My Stittsville garage floor slopes toward the house: what now?

A garage floor that slopes toward the house instead of toward the door is a drainage problem the 2024 Ontario Building Code directly addresses. Section 9.35.2.2 requires that where an attached or built-in garage is provided, the garage floor shall be sloped to drain liquids to the outdoors. A floor that drains toward the house is not what that clause describes, so it is worth having assessed.

Before deciding on a fix, have a contractor assess a few things. The slope may be the result of settling, heave, or the original pour. The 2024 Ontario Building Code notes in its appendix that frost heave results when moisture in frost-susceptible soil such as clay or silt freezes and expands, and that draw-down of water by fast-growing trees can decrease the volume of soil supporting floors-on-ground, causing settling. Canadian Building Digest 182 from the National Research Council notes that coarse-grained soils such as sands and gravels do not heave, whereas clays, silts and very fine sands will support the growth of ice lenses. A contractor can look at the slab condition, the base, and whether the slope is uniform or localized, and tell you whether a repair, a resurfacing overlay, or a full slab replacement is the right path. We found no published price for a garage floor replacement or repair that we can give you here.

If the assessment points to replacing the slab, a few Code provisions apply. Section 9.16.4.3 sets a minimum slab thickness of 75 mm exclusive of any topping. Section 9.3.1.6(1) requires a compressive strength of not less than 32 MPa for garage floors. Section 9.16.2.1 says not less than 100 mm of coarse clean granular material is placed beneath floors-on-ground, though it need not be installed under slabs in garages, carports or accessory buildings. Section 9.13.2.1 exempts garage floors from the dampproofing requirement. If the garage is attached to the house, section 9.35.3.2 notes that a construction joint shall be provided between the main building slab and a slab serving an attached garage, and that in clay-type soils subject to significant movement with moisture, the foundation depth of the garage may need to follow the main building's. Section 9.16.4.1 says dry cement shall not be added to the floor surface to absorb surplus water.

We found no City of Ottawa statement that the hardscaping contractor licence covers work on a floor inside a garage, so ask the City whether it applies to your job. We also found no City statement on whether replacing a garage floor slab requires a building permit. The City lists structural repairs or alterations among permit-required projects. Ask the City's Building Code Services before the old floor comes out.

If the work involves digging, whoever digs is an excavator under the Ontario Underground Infrastructure Notification System Act, 2012, and must submit a locate request through Ontario Dig Authority at least five business days before any digging begins. Ask who will submit that request.

A written quote should spell out the proposed slope direction and grade, the slab thickness, the concrete strength, how the base will be handled, removal and disposal of the old concrete, and what cold-weather protection will be used if the air temperature is below 5 °C during or after the pour.