The City of Austin preserves the natural resources that make Austin beautiful. Learn more about regulated-size trees, what impacts require a permit, digging into critical root zones, and tree survey requirements.
What you will find on this page:
- Regulated Tree Sizes
- What Impacts Require a Permit?
- Digging Into Critical Root Zones
- AIA Austin Tree Survey Samples
Regulated Size Trees
Regulated trees in Austin require a permit to remove or impact. You will need a Tree Ordinance Review Application (TORA) if your project requires you to:
- remove the tree,
- prune 50% or more of the canopy,
- and/or start an activity that may impact a tree or cause a disturbance to the critical root zone.
How to Measure a Tree
To calculate a tree’s diameter, measure the circumference of the tree from 4.5 feet above the ground (diameter at breast height or DBH), and divide by Pi (3.14). Trunks conjoined at soil level or above are classified as one, multi-stemmed tree.
- If the tree is on a slope, measure 4.5 feet above grade from the high side of the slope.
- If the tree has irregular swelling in the trunk, measure 4.5 feet above grade above or below the swell(s).
- If the tree is a multi-stemmed tree:
- Measure all the stems at 4.5 feet above grade.
- Take the largest stem diameter, and add it to half of the subsequent stem diameters.
For Example: A Cedar Elm has two stems measuring 18 inches and 16 inches at 4.5 feet above grade. The larger stem is 18 inches, so take half of the subsequent stem diameter (16 inches / 2 = 8) and add it to the largest stem measurement. Calculate multi-stem diameter: 18 inches + 8 inches = 26 inch diameter.
- If the tree is a leaning tree, measure at 4.5 feet above grade within the center area of the leaning tree.
What Impacts Require a Permit?
- Proposed removal of a regulated tree; and/or,
- Proposed impacts in the full critical root zone of regulated trees; and/or,
- Proposed pruning in excess of 25% of the canopy.
Tree Preservation Criteria
- A minimum of 50% of the critical root zone of all regulated trees must be preserved at natural grade, with natural ground cover.
- No cut or fill greater than 4 inches allowed within the 1/2 critical root zone. Piers with suspended slab may be permitted within the 1/2 critical root zone on a case by case basis dependent upon tree impact and at City Arborist staff discretion.
- No impacts allowed within 1/4 critical root zone.
Read the full Tree and Natural Area Preservation requirements, Section 3 of the Environmental Criteria Manual.
Digging Into Critical Root Zones
The Critical Root Zone varies with the size of its tree trunk. Any disturbance within the critical root zone has the potential to harm or kill a tree, particularly in combination with other impacts. Impacts can include disturbance to inches underground such as soil compactions from construction equipment and changes to grade.
The Critical Root Zone
In this example, the critical root zone extends 20 feet from the base of the tree. You can dig into the ground in the outer half of the critical root zone (in this example: between 10 to 20 feet from the base of the tree or the green zone).
1/4 Critical Root Zone
No impacts are allowed.
1/2 Critical Root Zone
No cut or fill greater than 4 inches.
Full Critical Root Zone
50% of the ground within this area must be preserved without impact.
AIA Austin Tree Survey Samples
View the AIA Austin Tree Survey Samples (PDF) for examples of what should be included in a tree survey.