Lot Grading and Drainage

When a new home is constructed, it is essential that the lot be graded properly to ensure that surface drainage is directed away from the building and so that it does not cause problems or damage to neighbouring properties. It is also important that the house be elevated so that the top of the foundation wall is at least 6 inches above the adjacent ground level, to avoid water entering any masonry weep-holes and to prevent rotting at the bottom plate of the framing.

The Ontario Building Code sets out the requirements for lot grading and drainage etc. during construction, in part as follows:

• 9.14.6.1 -The building shall be located and the building site graded so that water will not accumulate at or near the building and will not adversely affect adjacent properties.
• 9.15.4.3 - Exterior foundation walls shall be extended not less than 150 mm (6") above finished ground level.

Improper lot grading can result in bad surface drainage, ponding, flooding, foundation settlement or damage, basement dampness and other similar undesirable effects, and is one of the major factors resulting in customer complaints, callbacks, warranty repairs and legal proceedings following completion and occupancy of a dwelling.

The above adverse consequences are particularly regrettable as they can be largely eliminated by careful planning and the application of a few basic principles. The main factors to be considered in the grading of a lot after construction are that the lot should be sloped away from the house for a distance of at least 5 feet, no additional surface drainage should be directed onto adjacent properties and existing overall surface drainage patterns should be changed as little as possible.

For lots within current Plans of Subdivision, a Subdivision Grade Control Plan showing elevations and the overall drainage pattern is prepared by the Developer and must be conformed with as a condition of the issuance of a building permit.

For any other lot, an individual drainage plan for the lot would have to be prepared which takes into account the existing drainage patterns and elevations of adjacent properties, the street, etc.

The above information in the form of a Lot Grading Plan is required to be filed with the building permit application in accordance with the Town's Lot Grading Control Policy and Procedure Building.

The two most common types of lot grading are:

• Back to front - in this type the rear lot line is the high point, an elevated apron is created around the house and surface drainage flows forward to the street.
• Split - in this type, the house is the high point and the lot is graded so that surface drainage flows forward to the street and backward towards the rear lot line. The rear lot line is then generally drained by way of a swale and catchbasin system.

The location where most of the surface drainage problems occur is along the side lot lines between two houses, especially where the houses are in close proximity. In these locations a well-defined swale between the houses should be formed which allows surface drainage to be taken away from the house and directed forward or backward depending on which type of lot grading system is used.

In current Plans of Subdivision, lot grading is subject to the Town's Lot Grading Control Policy for Subdivisions and the Subdivision Grade Control Plan for the particular subdivision in which the lot is situated. 

For other lots, the lot must be graded so that surface drainage is directed away from the building and so that adjacent properties are not adversely affected by the surface drainage or additional runoff. Downspouts from roofs should discharge at grade onto a splash pad at least one metre away from the building and should not be directed towards adjacent properties. A well defined swale along the side lot line should be established.

The result of a well planned and properly executed grading and surface drainage system is a lot free of ponding, with no adverse effects to the adjacent properties to the ultimate enjoyment and benefit of all.

If you require any further information about lot grading and drainage, contact Building Department.