Tree Protection Zones in Toronto: How They're Calculated

What a Tree Protection Zone Is

A tree protection zone (TPZ) is the buffer around a tree, measured outward from the base of the trunk, where Toronto Urban Forestry prohibits excavation, grading, material storage, equipment traffic, and anything else that could injure the trunk, canopy, or roots. It applies to trees protected under the Private Tree By-law (Municipal Code Chapter 813), to trees on City streets, and to trees in areas regulated under the Ravine and Natural Feature Protection By-law (Chapter 658).

The TPZ is a minimum, not a suggestion. Urban Forestry's own policy notes that the published distances protect a tree's anchor and transport roots, but feeder roots responsible for water and nutrient absorption can extend beyond that boundary. Depending on the tree and the site, the City can require a larger zone than the table below sets out.

Hoarding and Fencing Requirements

Urban Forestry's specification calls for plywood tree protection hoarding, minimum 19 mm (three-quarter inch) thick, built 2.4 metres (8 feet) high, installed at the TPZ boundary shown on the approved tree protection plan. The height can come down where low branches require it, or where Urban Forestry approves an alternative. Within a City road allowance where visibility is a concern, 1.2 metre (4 foot) high orange plastic web snow fencing on a wood frame is used instead of solid hoarding.

Each barrier needs a sign, minimum 40 cm by 60 cm, mounted on all sides, identifying the area as a tree protection zone and warning that grade alteration, excavation, compaction, material or equipment storage, liquid disposal, and vehicle traffic are not permitted inside it.

Where the full minimum TPZ cannot be met because of site constraints, Urban Forestry can accept horizontal, on-grade root protection instead, designed by a qualified professional and approved before installation. Once protection measures are up, Urban Forestry has to inspect and approve them before any site work starts. Our tree protection and fencing service installs to these specifications and handles that sign-off.

What a TPZ Means for a Construction Project

Once a TPZ boundary is established, almost everything a construction site normally does is off-limits inside it. Urban Forestry's list of prohibited activities includes:

• Building, demolishing, or altering any structure, driveway, patio, deck, pool, or retaining wall
• Excavating, trenching, or changing grade by adding or removing soil
• Storing construction materials, equipment, or debris
• Discharging concrete sluice, paint, oil, or pool water where it can reach the root zone
• Parking or moving vehicles and equipment
• Cutting, exposing, or stripping roots, trunk, or branches

That is why the TPZ calculation matters before a design is finalized, not after. A foundation, driveway, or excavation footprint that lands inside the zone forces a redesign, a request to Urban Forestry to reduce the TPZ with alternate protection measures, or root pruning supervised by an arborist. Getting the number right at the planning stage avoids a permit application bouncing back for a corrected tree protection plan. Our guide to building or landscaping near a protected tree covers what counts as encroachment on an active site and what to do when the TPZ does not fit the lot.

The TPZ calculation itself is one of the six components Urban Forestry checks in a construction arborist report. A mismatch between the fencing shown on the plan drawing and the DBH-based distance in the written report is one of the most common reasons Urban Forestry sends a submission back.

Frequently Asked Questions

What is a tree protection zone in Toronto?

A tree protection zone (TPZ) is the area around a tree, measured from the outside edge of the trunk base, where the City of Toronto prohibits excavation, grading, material storage, equipment access, and any other activity that could damage the trunk, canopy, or roots. It applies to trees on City streets and private property protected under the Private Tree By-law, and to trees in areas regulated under the Ravine and Natural Feature Protection By-law. The boundary is marked on site with a physical barrier before construction starts.

How is a tree protection zone calculated in Toronto?

Toronto Urban Forestry sets the minimum TPZ radius from a table keyed to the tree's diameter at breast height (DBH), measured at 1.4 metres above ground. The radius increases in 0.6 metre steps as DBH increases, starting at 1.2 m for trees under 10 cm and reaching 6.0 m for trees between 91 and 100 cm. For trees over 100 cm DBH, the formula becomes 6 cm of protection radius for every 1 cm of diameter. Ravine trees get double these distances, or the drip line if that extends further. These are minimums: Urban Forestry can require a larger TPZ depending on the tree and the site.

What is the minimum tree protection zone for a 40 cm tree in Toronto?

A tree with a diameter at breast height between 30 and 40 cm falls into the 2.4 metre minimum protection distance band under Toronto's Table 1. If that same tree sits in a Ravine and Natural Feature Protection area, the minimum becomes the drip line or 4.8 metres, whichever is greater.

When can tree protection fencing come down in Toronto?

Not until the City formally releases the protection condition, which requires an inspection and sign-off, usually after an arborist submits a close-out report confirming the trees were not damaged. Removing the fencing before that release is a bylaw contravention regardless of how far construction has progressed. See our full guide on the close-out process for the notification sequence and what inspectors check.