Root zones and cutting roots in tree protection rules: Portland, Toronto and Sydney

This page reports what the official source says. It is not legal advice: ask the office named here. It sets out what one US city code, one Canadian city code and one Australian council guide say about the ground around a protected tree and about cutting roots. None of the three gives a single figure for how many roots may be cut. Each protects an area instead, and each treats work inside that area as something to be assessed, permitted or kept out. The wider list of protection standards is on the trees on building sites guide.

The three rules side by side

Place and source	How the protected ground is sized	What it says about work inside it
Portland, Oregon: City Code 11.60.030, amended effective January 1, 2025	A root protection zone with a minimum radius of one foot, measured horizontally from the face of the trunk, for each inch of tree diameter	Existing structures, paving and utilities in the zone may remain. New encroachments are allowed only if all of them together are under 25 percent of the remaining zone area and none is closer than half the required radius.
Toronto, Ontario: Municipal Code Chapter 813, Trees, and the city's tree and ravine permit page	A tree protection zone read from a table by trunk diameter at 1.4 metres. For a tree on private property it runs from 2.4 metres for a 30 to 40 centimetre trunk to 6.0 metres for 91 to 100 centimetres.	The city lists cutting, breaking, tearing, crushing, exposing or stripping a tree's roots among the acts that can injure it. A permit is needed to injure a protected tree.
City of Sydney, New South Wales: Tree guidelines for pruning, reporting and using an arborist, December 2025	A notional root zone and a structural root zone, worked out under Australian Standard 4970 (2025)	Intrusion of up to 10 percent of the notional root zone, with no recent encroachments and outside the structural root zone, is minor; over 10 and up to 20 percent is moderate; over 20 percent, or any intrusion into the structural root zone, is major.

Portland

Chapter 11.60 of the Portland City Code gives two paths. On the prescriptive path the zone is the radius above. The code names fencing of at least six feet of metal chain link on eight-foot posts at the edge of the zone, signs stating penalties, and a list of what is prohibited inside the zone: ground disturbance and construction activity including vehicle access, storage, stockpiling, buildings, paving, underground utilities, excavation or fill, and trenching. It counts in-ground irrigation as an encroachment and says landscaping required under Title 33 is not one. On the performance path, an arborist who has visited the site prepares an alternative zone based on the tree's size, location, extent of root cover, species, health and past impacts, signs the plan, and the city may have it peer reviewed or require a performance guarantee. Section 11.60.040 of the same chapter says pruning or root cutting must follow proper arboricultural practices, using clean and sharp tools.

Chapter 11.50 of the same code ties the rules to work near roots. It names development with ground disturbance, or a staging area over 100 square feet on unpaved ground, inside the root protection zone of a private tree 12 or more inches in diameter, or a city tree six or more inches in diameter, as the kind of activity it covers.

Toronto

Chapter 813 of the Toronto Municipal Code (the PDF is dated May 12, 2022) defines injure as any act that will harm a tree's health in any manner, including failure to protect it to the General Manager's standards. It bars injuring, destroying or removing a tree with at least one stem of 30 centimetres or more, measured at 1.4 metres, without a permit. Its permit conditions say an injury permit is carried out by or under the supervision of an arborist, only after a building or demolition permit, and with tree protection barriers installed before work starts. The city's permit page gives the table of tree protection zones by trunk diameter. For trees in ravines and natural areas the sizes in the table are double for trunks of 10 centimetres or more, or the dripline if that is greater. The page adds that if construction on site will affect the zone, a permit to remove or injure is needed, and that if it will not, the city expects a tree protection plan made with an arborist. It also states that roots do not cause lifts or cracks in properly built and well-kept infrastructure, which is the city's own wording on a common complaint.

Sydney

The City of Sydney guide says Australian Standard 4970 gives formulae for two zones. The tree protection zone is the minimum area needed for a tree's health and can extend well beyond the crown. The structural root zone is the smaller area around the base that usually holds most of the large structural roots. Moderate intrusion needs the consultant arborist to review the impact and show the tree will stay viable. Major intrusion needs alternative designs to be explored. The guide says that where the zone is reduced in one place it should be offset by an equal extension in another contiguous area, to avoid a net loss of soil area and volume.

What the three do not say

None of these pages states a share of roots that may be cut from a tree, or a diameter of root below which cutting is free of consequence. Portland and Sydney express the limit as a share of an area, and Toronto leaves the root question to the permit. Sizes, fees and procedures on these pages belong to the offices that publish them and are read here on October 9, 2026 only.