Facility Management: How to Protect Apartment Building Foundations from Thirsty Tree Roots
Trees are a desirable amenity to residents and a way for property owners to add value and beauty to an apartment community. But those big, leafy green trees that provide cooling shade for apartments can in fact be causing considerable damage to the building’s foundation.
Trees absorb a great deal of water that can impact a slab-on-grade foundation, which are more commonly used in Texas than slab-over-pier foundations. Cracked walls and doors that don’t close can result from a damaged foundation caused by trees being too close.
Roots usually don’t directly damage a foundation, although they can penetrate existing cracks. More commonly, roots deplete moisture under and around a slab-on-grade foundation, especially during drought.
The rule of thumb, says GeoDynamics President Jim McNeme, a Dallas-based foundation inspector who specializes in apartment buildings, is that a 12-inch diameter tree will take 200 gallons of water out of the soil per day, potentially causing a slab-on-grade foundation to move, also known as settling.
“Trees can get expensive when you have to deal with them,” said McNeme. “They can make slab foundations settle, which can cause all sorts of damage to buildings.”
A visit a couple of years ago to the Texas Gulf Coast provided a stark reminder of what can happen to an apartment community when it is “under siege” by large trees.
“In about 70 percent of the cases on various apartment complexes, which are spread out over Harris County, the worst problems were those buildings closest to where they have large trees,” McNeme said. “You take the drought and you add in the desiccation that the mature trees cause, and that’s what was killing those buildings down there.”
Because the Texas Gulf Coast has high moisture content in soil, slabs there typically don’t shift like those that experience the normally drier conditions of North Texas. Most slab issues that McNeme has experienced at apartments in Houston are because of mature trees soaking up water around the foundations, especially during recent drought conditions.
Repairing the foundation by drilling piers in or around the slab can run into the hundreds of thousands of dollars. “It’s certainly a worst case scenario when we have to put in piers. But if you have a properly designed pier, that pier is going to keep the slab from settling.”
Installing Root Barriers to Protect Building Foundations
An alternative to drilling peers, McNeme said, is installing a root barrier.
A root barrier – made with an impermeable, durable material that can be covered in soil for an extended period of time – is applied where there is expansive clay soil to prevent roots from depleting the ground of its moisture. The barrier is installed between the tree and building(s).
A 2002 report published by Texas A&M professor and landscape horticulturalist Dr. William C. Welch suggests that a root barrier can reverse foundation settlement resulting from shrinking soil.
While root barriers require time to work, McNeme says they are worth a shot to avoid cutting down a tree that brings shade and protection to residents.
“I very rarely tell a client to get rid of the tree,” he said, adding that he’s seen several examples of large trees that haven’t caused problems next to foundations. “I would rather work around the tree because it adds so much value to the property.”
That comes from personal experience: A tree has caused minor foundation issues and small cracks in the sheetrock of McNeme’s North Texas home. But the aesthetic benefit of the big oak is more important to him.
So he copes and leaves the chainsaw in the storage building.
“I’ve come to a peace treaty with my tree,” he said. “I know it’s going to mess with me some, but I like some of the other stuff about it.”