The City of St. Thomas Site Alteration By-law regulates activities such as placing or dumping fill, removing topsoil, and altering the grade of land within the city. The by-law was originally approved at a special meeting of Council on November 1, 2010, and was updated effective December 1, 2025.

Altering the land's surface, or grade could interfere with the way water moves off our property. Water that can't drain off can cause problems for yourself or your neighbour.

A permit process has been set in place to balance environmental and administrative considerations for site alterations. The requirements of a permit will grant the city the ability to ensure that:

  • Unanticipated drainage and site alteration is prevented;
  • Appropriate drainage patterns are maintained;
  • Interference and damage to watercourses or water bodies is limited;
  • Water quality is maintained;
  • The use of hazardous and/or improper fill is prevented;
  • Erosion and sedimentation is prevented;
  • Natural heritage features such as wetlands, valley lands and wood lands and areas of archeological resources are protected; and
  • The city's natural topography, soils and vegetative features are considered.

What you must know


The land you own, where your home sits, is called a lot and in some instances designed with a swale in the backyard or side yards. This shallow ditch or depression in the ground, guides surface water safely off your property. It must be protected and maintained, along with the flow of natural waterways such as streams. This ensures that homes don't experience flooding from spring thaws or rainstorms and that yards don't suffer from ponding or collected water that doesn't go anywhere.

When homeowners plan a new garden and landscaping projects, these swales must be preserved.

The following are a few guidelines to help you determine if a permit is required

  • When you alter the grade on your property by more than 150 mm (6") by adding or removing soil.
  • When you install a retaining wall.
  • When you construct a pool, deck, fence, shed, garage or other structure.
  • When you install a pond.
  • When you install a driveway or sidewalk.
  • When you install raised gardens or flower beds.

Applying for a site alteration permit


If a Site Alteration Permit is required, the applicant should submit the following items:

Permits Fees & Deposits


The site alteration permit fee $110 + HST (as per the Site Alteration By-Law).

Fees for the processing, administration, and inspection of a permit are charged in accordance with the City’s Fees and Charges By-Law. In some cases, a security deposit may also be required.

Deposits are returned after City staff have inspected the site and confirmed that the project has been fully completed and meets the applicable requirements. Deposit amounts are established through the Fees and Charges By-Law.

For a typical residential site alteration, the required deposit is $1000. For all other projects, the deposit is calculated as a percentage of the construction value, based on the cost of grading, erosion and sediment control (ESC) works, and site stabilization.

For more information, please refer to the Site Alteration By-Law.

Length of time a site alteration permit in effect


A Site Alteration Permit will remain in effect for a period of six (6) months from the date of issuance. A permit may be extended once, upon written application to the Inspector, prior to the date of expiry.

When in doubt, check it out! Help is always available.

For more information please contact the Environmental Services Department at 519-631-1680 x4228 or x4167 OR the Planning and Building Services Department at 519-633-2560.