Building in a Green City – Protected Trees

Building in a Green City – Protected Trees

In recent years, in an effort to protect valuable trees in the inner city and to further protect heritage trees, the City of Austin has established guidelines for building in close proximity to “protected trees”. The City Arborist has defined a protected tree as one when measured 4.5 feet above ground is 19” and greater in diameter.

Building in proximity to protected trees can be confusing at best. The City Arborist has established guidelines to determine where a structure can be located to a protected tree based on the tree’s diameter. The proximity of a building is based on the size of the ‘critical root zone” (CRZ).

The critical root zone is an imaginary circle centered on the trunk of a tree that has a diameter in feet that is twice the number of inches of the tree’s trunk diameter. For example, a tree with a 20” trunk would be represented by an imaginary circle that is 40’ in diameter. When building in proximity to a protected tree, a structure cannot be located within ½ of the critical root zone or as in the example above, no closer than 20’ from the protected tree.

The City Arborist will allow for limited construction within ½ the CRZ with approved shallow foundation systems. Structures has had extensive experience working with architects and builders in establishing such solutions, including the Auction Oak Deck Structure at Republic Park.

The project consisted of the design of a 4,000 square foot deck under the central auction oak tree. The new deck structure was carefully designed such that its construction had minimum to no disturbance of the existing oak trees’ root systems. The deck also provided protection for the tree’s root systems and allows visitors to enjoy sitting under the tree.

Please let us know if we can be of any assistance in determining the proper solution for your new construction project. For more information you can visit the City’s Arborist website.