Treat your tree with kindness during a remodel
February 19, 2010
Treat your tree with kindness during a remodel
By Morgan Zenner
Landscaping is a big part of a home’s character and value, especially trees. As trees mature, their root systems become intricate and widespread. These root systems are the lifeline of trees and can be harmed easily during a renovation project if the tree is close to the home or work area.
According to Peter Michelson, of Renewal Design Build, homeowners must weigh the benefits and losses when deciding to work around a tree. It’s a remodeler’s responsibility to help them discover what is in their best interest.
“In all cases, the first thing to do is have the tree assessed by a certified arborist,” Michelson says. An arborist is professionally trained in the needs and care of trees.
“Many trees appear to be healthy on the outside, but it’s actually not. It is important to know this before going through great lengths to preserve a tree only to have it may die a couple years later,” he says.
Arborists take species, size, maturity, location and condition into consideration when assessing the tree. Sometimes it’s not always best to save the most mature trees, which are more sensitive to their surroundings compared to younger, vibrant trees.
If the arborist deems the tree healthy, homeowners must ensure their building and design process meets the requirements of the local building department. Each jurisdiction has different requirements, and those requirements are updated yearly. These building codes are usually accessible on a county Web site.
Saving a tree during a remodel can add costs to the project, and it is important for homeowners to consider the value of saving the tree. In addition to the obvious aesthetic beauty of a tree, they provide shade to homes, which can lower utility costs during the summer months and provide wind reduction during the winter. Trees also provide privacy, noise control from neighbors and street traffic. Trees naturally balance the flow of oxygen and carbon dioxide and help prevent flooding.
“People don’t realize how much water trees soak up until they remove them,” Michelson says. “Water collected on the leaves and in the ground greatly reduces the chance of flooding.”
Tree considerations
Assume that your client decides to keep a tree that is in close proximity of the addition you’ve been hired to build. There are ways to work around a tree safely.
According to Michelson, there are two roots zones to consider. The first is the structural root plate, which are the large stabilizing roots that keep the tree from falling over. The second is the critical root zone, through which nutrients and water are absorbed.
For ideal root growth, soil should have 50 percent of pore space. The pore space, which is filled with water and oxygen, helps roots develop. During construction, heavy equipment can compact the soil around the root keeping oxygen and water from getting through.
The critical root zone is detected by drawing out the outer edge of the head of the tree and adding on 1 foot for every inch in diameter from that edge. This area is known as the drip line. The drip line must be protected during construction, otherwise the tree runs the risk of dying.
To avoid soil compaction, “add four to six inches of mulch in that entire area of the critical root zone, and, as added protection, have an arborist pump healthy organics into the soil to sustain the trees nutrients,” Michelson says.
Say a tree is in the direct line of work, where the crew crosses back and forth over the critical root zone to complete the job. Over time, this can damage the tree as well.
“In this case, it may be better to put six to eight inches of mulch around the critical root zone and without harming the tree, place two-by-four soldiering around the trunk of the tree to protect it,” Michelson recommends. He adds that trunk protection does not require stakes in the ground, which can harm the root system.
During the project, be cognizant of where brushes and other tools are washed out to avoid soil contamination. The mulch helps to soak up harmful chemicals, but it’s not a full-proof barrier. It’s always good to have the soil treated after work is done.
Ways to build around a tree
If remodeling is taking place within 20 percent of the tree’s critical root zone (the maximum amount without killing the tree), you probably cannot build on a continuous footing/foundation system. The best way to build is on piers.
Building on piers may require a structural engineer to identify beam and floor joist sizes. Unlike a traditional foundation, piers are vertical columns placed into the soil in concrete holdings. The beams are erected out of the soil to hold up the walls of the home. Piers are sturdy, and they allow for oxygen and water to enter the root system.
“I recommend getting clearance for plywood for this type of foundation because the chemicals on treated wood are not always protective against mold and rotting,” Michelson says.
Another option is known as bridge footing. This process requires you to carefully expose roots by using an air shovel. This step alone can cause major damage to the roots if it is not done correctly. Damage to one major root can cause 5 to 20 percent loss of the root system.
Once the roots are exposed, you form a footing to bridge over the root. Re-bar concrete allows space around the root. Place posts in the concrete of the bridging to hold up the walls of the home.
“Bridge footing is probably the most expensive way to go about building around a tree, but it is very good in situations where the roots extend right where you want to build,” Michelson says.
A third option involves using a helical pier. Basically, a helical pier is a large screw placed in the ground. The helical pier is drilled deep into the ground until it hits bedrock. The compact nature of the soil holds the pier in place and provides a stable structure to build upon.
This process is known for being quick and easy and requires no clean up. It’s possible to drill the piers into the ground in the morning and start on the framing by the afternoon. However, an engineer is needed to determine how many helical piers are needed, at what size and the approximate depth of drilling.
Michelson estimates working close to tree roots can add 5 to 10 percent onto the site cost of the project, an extra cost that needs to reflect the value of the tree.
As a remodeler, Michelson says that finding a realistic arborist is essential. “You want someone who is balanced in their approach and calls it when it’s not in your best interest to preserve the tree,” he says. He adds it would be helpful to have your arborist teach your construction team how to work safely around trees.
Photo courtesy of Lee Mackenzie, Mackenzie Design Build Inc.