A construction arborist report is a site-specific document that identifies every protected tree on and adjacent to your property, assesses each tree’s condition, and specifies exactly how those trees must be protected during construction. Without it, Toronto and most GTA municipalities will not release a building permit for any project that falls within a tree’s regulated buffer zone.
What Triggers the Requirement
The report requirement kicks in when proposed construction, grading, excavation, or underground work falls within the protected area of a regulated tree. In Toronto, that means any tree 30 cm or more in diameter at breast height (measured at 1.4 metres above ground) on private property, under Chapter 813 of the Municipal Code. Properties in ravine and natural feature areas face a second layer under Chapter 658, which protects trees of any size.
Other GTA municipalities set their own thresholds. Mississauga’s permit guide starts at 15 cm. Burlington at 20 cm. The protected diameter on a tree two streets away could differ from yours. If you are not certain which bylaw applies, check the relevant city permit guide before assuming your project is exempt.
The trigger is proximity, not removal. You can be building an addition that does not touch a single branch and still need this report if the excavation encroaches on a root zone.
The Six Components Cities Expect to See
A complete construction arborist report covers six distinct elements. Missing any one of them is the most common reason Urban Forestry sends a submission back.
Tree inventory. Every protected tree on the site and any adjacent trees whose roots or canopy extend into the construction area must be catalogued. The inventory lists species, trunk diameter (DBH), measured at 1.4 m, and GPS or survey-referenced location. Trees on neighbouring properties that fall within the regulated buffer get included too. The inventory is the foundation everything else is built on.
Each tree also receives two condition ratings, assessed separately: a health rating (crown density, foliage colour, disease or pest activity) and a structural condition rating (defects in the trunk, root flare, and scaffold branches). Both ratings affect how the arborist calculates the tree’s retention value and how the city weighs it.
DBH and tree protection zone calculation. The tree protection zone (TPZ) is a buffer calculated from the trunk diameter. The industry standard formula is based on DBH: a common approach applies a minimum radius derived from the trunk size, though specific multipliers vary by municipality and species. The TPZ defines the area where no excavation, material storage, equipment, or grade change is permitted. The city checks the math.
The construction impact assessment identifies which activities will come closest to retained trees and evaluates the likely outcome. Root severance from trenching, compaction from equipment, grade changes that could suffocate roots, and soil contamination from concrete washout are common concerns. Where impacts are significant, the arborist may recommend removal over a slow post-construction decline.
Tree preservation plan. The written preservation plan describes what will be done to protect each retained tree through every phase of construction: excavation, framing, mechanical rough-in, and landscaping. It specifies arborist monitoring requirements and post-construction care. This is the prescriptive section the general contractor is expected to follow on site.
A separate formal plan drawing accompanies the written report. It is scaled and drafted (typically in AutoCAD) and shows the exact placement of tree protection fencing, the boundaries of each TPZ, staging areas, equipment routes, and material storage zones. The contractor and city inspector reference this drawing during site visits. Cities treat the written report and the plan drawing as a paired package. Submitting one without the other leaves the application incomplete and can trigger a revision request.
Why Urban Forestry Rejects Reports
Most rejections come down to a small set of recurring issues.
Inventory gaps are the most frequent. Arborists who measure only the trees directly on the applicant’s lot often miss adjacent trees whose root zones extend under the proposed footprint. City reviewers check the site plan against aerial imagery and flag missing trees immediately.
Condition ratings without field observations are another common problem. A report that assigns ratings without noting observable defects, crown dieback percentages, or recent stress events reads as a desk exercise. Urban Forestry reviewers expect field-specific observations.
TPZ calculations that do not match the municipality’s formula produce fencing layouts the city will not accept. Different municipalities use different multipliers and may require peer review of the calculation methodology.
A missing or inconsistent plan drawing stalls more permit applications than any other single issue. If the drawing does not match the written report (different tree numbers, inconsistent fence placement, staging areas shown inside a TPZ), the city returns the package and the review clock resets.
Reporting prepared for a previous application on the same site, or borrowed from a similar project elsewhere, also fails. Cities compare reports against current permit drawings. If the report references a structure that does not match your current set, reviewers flag it.
The Difference Between a Construction Report and a Removal Report
These are not interchangeable documents. A tree removal report supports an application to take a tree down. A construction arborist report focuses on keeping trees alive through a build. Some projects need both: a developer may need to remove two trees and preserve six others on the same site.
If you are unsure which document your project requires, the which report do I need page walks through the distinction by project type.
What Happens During Construction
Submitting an approved report is not the end of the arborist’s involvement. Most municipalities require periodic monitoring visits during construction to confirm that protection measures are in place and intact. A stop-work order can follow if fencing is moved without authorization, material is stored inside a TPZ, or grade changes occur without arborist sign-off. The monitoring requirement is stated in the approval conditions and is the builder’s responsibility to schedule.
Getting the Report Right in Toronto
Toronto’s Urban Forestry review can generate requests for revisions or additional information when a report is incomplete. Toronto does not publish a standard review time in its current application guidance, so project schedules should allow for municipal review and possible revisions.
The practical consequence is simple: an incomplete submission delays your permit, and every trade waiting behind it. The construction arborist report we prepare includes the full six-component package, the plan drawing, and the spec addendums contractors need on site, formatted to the standards your municipality expects.