Trees on building sites: the protection standards

When a building project puts work near trees, a standard or a city rule usually sets out how the trees are surveyed, how much ground around them is kept clear and what fencing marks that ground. This page describes what each one covers. Standards are bought from the publisher, and the full text is the only complete source.

Words in these documents

Each country uses its own term for the ground kept clear around a tree. They are close, but they are not the same thing, and each document defines its own.

Term	Used in	Plain meaning
Root protection area	UK	Ground around a tree kept clear of building work
Tree protection zone (TPZ)	US, Australia, Toronto	Area where digging and building work should be avoided
Critical root zone (CRZ)	Ottawa, Austin	Root area a city rule sets by trunk size
Structural root zone	Australia	Smaller area around the base needed for stability

United States

The standard is ANSI A300 Part 5, titled "Management of trees and shrubs during site planning, site development, and construction". The Tree Care Industry Association describes it as a document to use together with the rest of the A300 standard when writing specifications for tree care operations. Its store notice for the 2019 edition says that edition is no longer in effect as of November 16, 2023 and is replaced by the ANSI A300-2023 standard. See the TCIA store notice.

The text of the 2012 edition is hosted by a US municipality. It defines a tree protection zone as the area surrounding a tree, defined by a specified distance, in which excavation and other construction related activities should be avoided. It defines tree protection zone barriers as devices such as fencing, berms or signage that define and limit access to the zone. It also defines a root protection zone, which may extend beyond the tree protection zone. It does not use one fixed multiplier for all trees. Newer editions may differ, so this is a description of the 2012 wording. See the 2012 edition copy.

City rules sit on top of the standard. Austin's page for commercial and multifamily property says a minimum of 50% of the critical root zone of all regulated trees must be preserved at natural grade, with natural ground cover, and no cut or fill greater than 4 inches is allowed within the half critical root zone. It adds that no impacts are allowed within the quarter critical root zone. See the Austin commercial and multifamily trees page.

Canada

Canada has no single national construction standard on the pages linked here. The rules are municipal.

Toronto

Toronto says a Tree Protection Zone is the area around a tree that must be protected during construction work to preserve the health of the tree. If any construction work on site, including access or storage, will impact a zone, a permit is needed. If it will not, no permit is needed, but trees near the work must still be protected and a Tree Protection Plan completed in consultation with an arborist. The city recommends an arborist measure the zone.

Trunk diameter	Private property	City street
30 to 40 cm	2.4 m	2.4 m
41 to 50 cm	3.0 m	3.0 m
91 to 100 cm	6.0 m	6.0 m
Over 100 cm	6 cm per 1 cm	6 cm per 1 cm

These are the minimum zone sizes in the city's table, shown in part. The full table has more rows, including trees in ravines. See the Toronto permit page.

Ottawa

Ottawa's Tree Protection By-law says people working near protected trees must, unless the City authorises otherwise, put up a 1.2 m high fence around the outer edge of the critical root zone before other site work and keep it until the work is complete. They must not place material or equipment in the zone, change the grade in it, or extend a hard surface in it. The city states the critical root zone as 10 centimetres from the trunk for every centimetre of trunk diameter, and says failing to protect a tree that is not approved for removal is an offence. See the Ottawa protecting trees page.

United Kingdom

The standard is BS 5837, Trees in relation to design, demolition and construction. Recommendations. The BSI Knowledge page lists the 2012 edition as current and under review, published April 30, 2012. It says the edition replaced the 2005 one, which is withdrawn, and that its recommendations can be applied whether or not planning permission is required. BSI names arboriculturists, architects, builders, landscape architects, land managers, contractors and statutory undertakers as people it is relevant to. See the BSI Knowledge page.

The government's planning advice on ancient woodland and veteran trees says a tree survey should follow guidance in BS 5837. It gives separate buffer figures of its own. For ancient woodland it says a buffer of at least 15 metres from the woodland boundary to avoid root damage, which it calls the root protection area. For ancient and veteran trees it says the buffer should be at least 15 times the diameter of the tree, or 5 metres from the edge of the canopy if that area is larger. These are the government's figures for that case, not a statement of the BS 5837 root protection area rule. See the government advice for planning decisions.

Australia

The standard is AS 4970, Protection of trees on development sites. Standards Australia lists AS 4970:2025 as current, published 2025, from committee EV-018 Arboriculture, and as superseding AS 4970-2009. See the Standards Australia catalogue entry.

The City of Sydney guidelines, dated December 2025, describe what the standard covers. They say the tree protection zone is the minimum area needed for a tree's health and can extend well beyond the canopy, and the structural root zone is the minimum area the tree needs for stability. They say the standard does not argue for or against development, or for or against keeping trees, but provides a process for managing trees through development. Reports sent in with a development application have their structure set out in the standard. The guidelines name an arboricultural impact assessment and say zones come from formulae in the standard. See the City of Sydney tree guidelines.

New Zealand

What applies in New Zealand is a council rule. Auckland Council says that for a tree protected through district plan rules, a resource consent may be needed, and that extensive works may also need an arborist's report written by a qualified arborist. See the Auckland protected trees page.

Side by side

Country	Document	Edition per publisher
US	ANSI A300 Part 5	A300-2023 replaces the 2019 edition
Canada	City rules, Toronto and Ottawa	City pages, no edition named
UK	BS 5837	2012, current, under review
Australia	AS 4970	2025, replaces 2009
New Zealand	Not stated	Council rules, Auckland

Before work starts near a protected tree, the land owner and the council decide what applies. For what a protection order or permit covers, see tree protection orders, bylaws and permits.