If there is a protected tree anywhere near your planned addition, deck, pool, or laneway suite, the tree protection zone around it is not a formality you deal with after the design is done. It is a boundary that has to be drawn before the design is finalized, because everything a construction site normally does inside that boundary is prohibited.
This is the piece homeowners and builders usually miss until a permit application bounces back. The tree protection zone (TPZ) is a fixed distance set by trunk diameter, and Toronto’s Urban Forestry department checks proposed construction against it before the building permit is released.
The Zone Is Set by Trunk Size, Not by the Site Plan
Toronto calculates the minimum TPZ from the tree’s diameter at breast height (DBH), measured at 1.4 metres above ground. A tree between 30 and 40 cm DBH needs a 2.4 metre buffer measured from the outside edge of the trunk. That distance climbs in steps as the tree gets bigger, up to 6.0 metres for a tree between 91 and 100 cm, and beyond that the formula switches to 6 cm of radius for every 1 cm of diameter. If the tree sits in a Ravine and Natural Feature Protection area, the minimum doubles, or extends to the drip line if that reaches further.
None of this depends on where your foundation, driveway, or pool shell was drawn. The tree sets the number, and the design has to work around it. A footprint that overlaps the TPZ is a problem the city will flag, not a detail it will overlook.
What Counts as Encroachment
Once the TPZ boundary is established, the list of prohibited activity inside it is long and covers most of what a build site does day to day: excavating or changing grade, storing materials or equipment, parking or moving vehicles, discharging concrete sluice or paint where it can reach the roots, and cutting or exposing roots, trunk, or branches. Building or altering a structure, driveway, patio, deck, pool, or retaining wall inside the zone is off-limits without a separate approval.
A contractor staging lumber against the fence line, a skid steer parking inside the zone between tasks, or a downspout redirected to drain across the TPZ during a wet week are all encroachments, even when nobody touches the tree directly. Urban Forestry does not distinguish between deliberate root cutting and incidental site traffic; both count as interference with a protected tree.
Why Forestry Wants an Arborist Report With a TPZ Plan
Because the zone has legal weight, Toronto’s Urban Forestry department will not release a building permit that has a protected tree near the proposed work until it has reviewed a construction arborist report with a tree protection plan attached. The report identifies every affected tree, calculates its TPZ, and assesses how the proposed construction will affect its root zone and canopy. The plan is the scaled drawing that shows exactly where the fencing goes, so a site inspector can check it against the site rather than against a written description.
The construction-related permit fee reflects how seriously the city treats this: a tree removal tied to construction costs $436.39 per tree, compared with $145.87 for a standard non-construction removal. Forestry review is more involved when a build is in play, and the fee schedule follows the same logic as the TPZ requirement itself: construction near a protected tree gets more scrutiny than the tree alone would.
A design that has not accounted for the TPZ is one of the most common reasons a submission gets sent back. If the fencing shown on the drawing does not match the DBH-based distance in the written report, or the proposed footprint clips the zone with no mitigation plan attached, forestry holds the file until it is corrected. That correction cycle is avoidable if the TPZ is calculated before the design is locked in, not after a first rejection.
What Happens to Your Permit Application
A building permit application with a protected tree nearby gets flagged and routed to Urban Forestry for review before it can be released. That review sits outside the building department’s normal timeline. Our guide to forestry clearance holds covers the full review sequence, but the short version is that the file does not move until Urban Forestry has confirmed the protection plan is adequate and, once construction starts, that it is being followed on site.
Periodic site inspections during construction produce the record forestry wants at the other end of the project, when it is time to release the protection condition and let the fencing come down.
When the TPZ Does Not Fit the Lot
On a smaller urban lot, the minimum TPZ for a mature tree can eat into the buildable footprint more than the design allows for. Toronto’s specification anticipates this: where the full TPZ genuinely cannot be met, Urban Forestry can accept horizontal, on-grade root protection instead of the standard fenced buffer, but it has to be designed by a qualified professional and approved before installation, not improvised on site once excavation is already underway.
The other route is root pruning, done under an arborist’s supervision, to allow a reduced footprint without the unsupervised root damage that comes from a backhoe operator working blind. Either option needs to go through Urban Forestry before it appears on a permit drawing. Showing up with a reduced TPZ on the plans and no supporting approval is the same as ignoring the requirement altogether from the city’s point of view.
If a protected tree sits close to where you want to build, work out the TPZ and the options for it before the architect finalizes the drawings. Contact us with your address and what you are planning, and we will calculate the zone, flag any conflict early, and prepare the report Urban Forestry needs to release the permit.