Protecting Trees During Construction

Many of the tree health issues and failures we see are the direct result of improper protection during construction. If you plan to preserve a tree growing within the construction zone during a new build, remodel, addition, or pavement installation, the trees must be protected. During the project, temporary construction fencing, as seen above, is placed around the root protection zone of a tree to exclude construction activities from that zone.

Why Protect Trees

Without protection of the root system, compacted soil from heavy construction vehicles, like those seen above, could significantly inhibit water and air penetration to the root system. Excavation for the laying of foundations and installation of underground utilities could sever and crush crucial root systems. Laying impermeable driveways, sidewalks, or road pavement over a mature root system could also damage the roots by inhibiting water and air penetration which could lead to poor root vigor or death. Without fencing, the tree is also at risk of branch breakage and trunk damage as heavy equipment moves nearby.

How to Protect Trees

The size of the area to be protected is calculated based on the size of the tree at the time of construction and estimates the location of the most important tree roots, or the critical root zone (CRZ). The International Society of Arboriculture (ISA) recommends protecting a one foot radius for every inch of tree trunk diameter as measured 4 ½ feet above the ground. For example, a tree with a trunk diameter of 6 inches as measured at breast height should be protected six feet away from the base of the trunk all the way around the tree.

Another way to estimate the size of the tree’s critical root zone is to determine the tree’s dripline, or the line directly under the outermost edge of the canopy. Whether calculating the critical root zone based on the trunk diameter or the dripline, use whichever estimate gives the greater area.

If the entire critical root zone cannot be protected and damage to the root zone is unavoidable, an ISA-certified arborist should oversee the root zone management. The amount of acceptable root loss depends on the site conditions and tree species and can be minimized with other protection measures including ground protection and selective root pruning.

Place the temporary construction fencing the calculated distance from the tree trunk for the duration of the construction. Use highly visible signs to identify the root protection zone and communicate the importance of excluding all construction activities in the root protection zone to construction contractors. As construction permitting rules vary from city to city, check with your planning department for tree protection requirements. Most local municipalities require tree protection as part of the building permit process.

If you would like more detailed information, the OSU Extension Service has published a helpful guidebook document which outlines best management practices for tree protection on development sites.

Protecting established trees during construction will promote tree health for the entire life of the tree.