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Home Inspections: Vegetation, soil moisture affect foundations

By By Gabe Semenza
April 17, 2013 at 3:03 p.m.
Updated April 16, 2013 at 11:17 p.m.


Ask the home inspectors

Have stories or lessons regarding homes - their operation or importance in daily lives? Contact Gabe Semenza at 361-676-1480 or gabe@semenzainspections.com.

The more real estate inspections I perform, the more damage I view from trees near homes.

For that and other reasons, trees are double-edged plants.

They provide beauty, shade, privacy or food. But they can also damage your home, harbor pests, crack foundations and disrupt plumbing.

Short of removing all the trees and shrubs from your landscape, which I don't recommend, what can you do to minimize their harm?

Tree branches can scrape, gouge and uplift shingles. They can poke into siding. They even hold moisture against wood features such as soffits and fascia boards, spurring rot.

Trees near homes also become highways for four-legged and other critters. I see plenty of large droppings on roofs - from squirrels and raccoons - and signs that cats prowl up there, too.

Low-lying shrubs also offer shelter to smaller pests - from scorpions and ants to beetles and cockroaches. Once nestled into and near landscaping shrubbery, they quickly can become a nuisance.

Those potential effects are typically in plain view.

It's what might be going on under the surface soil that worries Jay Conner, president and chief executive officer of Texas-based MLAW Engineers and MLA Geotechnical.

"Trees are thirsty. They need water," Conner, whose companies provide foundation, structural and soils engineering services, said. "Oftentimes, their roots drink the moisture out of the soil under and near the foundation. Then, the soil shrinks and the foundation settles."

Foundations and vegetation - trees, shrubs and other plants - compete for moisture in the soil. Because vegetation is a living entity, it usually wins, Conner said.

"We call this 'edge drop' and we find it's more likely to occur around the perimeter of a foundation," Conner said. "But we've also seen tests that show roots will grow 30-40 feet under the slab to reach water."

For foundations to perform as intended long term, soil consistency is crucial. When certain soil types dry, they shrink, and the foundation can settle downward. If this soil becomes too wet, it expands and can push the foundation upward.

These possibilities can become more accelerated during drought times.

"It's the sudden changes in soil moisture that often cause the problems," Conner said. "If it's a subtle change, slow, it's not going to be as much of a problem. A foundation can move and bend and flex, and it'll be OK if it does so slowly. But any quick movement can bend and damage it."

While under a home, tree roots can also penetrate plumbing pipes, cause leaks and other problems.

So, what can you do to minimize potential harm from trees and shrubs? While determining whether roots specifically cause plumbing or foundation problems is typically beyond the scope of a Texas home inspection, these tips should be useful for homeowners and homebuyers.

To avoid damage to roofs, siding and other exterior components, simply keep overhanging limbs trimmed several feet away from the home. Doing so will also help to shorten the critter highway and shave down the time you spend cleaning debris out of gutters.

Keep in mind limbs can dip and dive during windstorms, so account for that when trimming.

Trimming shrubs to 18-24 inches away from the home will help to keep moisture away from siding. This alley also offers you access to these areas and maintains a sizable air gap between pests and home entry points.

To help counteract the effects of thirsty plants on foundations and plumbing, Conner recommends you properly use soaker hoses - those perforated hoses often called "drip hoses."

Use soaker hoses in moderation to keep the moisture content of the soil consistent around the home's perimeter. Calculating the amount of water needed - which varies based on rainfall, shade levels, geography and more - is beyond the scope of this column.

One simple rule of thumb, though, is to keep the soil around your foundation damp to the touch but not sopping wet.

"I have seen soaker hoses do harm when they're used incorrectly," Conner said. "If you add too much water, you can get edge lift. Your foundation can heave upward. You don't want to go quickly from wet to dry or dry to wet, which is where stress can happen."

There's no magic bullet to fully nullify vegetation's effects on your home so long as you have nearby trees and shrubs.

But like all things related to Mother Nature, you can find a happy medium - enjoyment of your trees and shrubs without the headaches they sometimes cause.

Gabe Semenza is Texas Licensed Professional Inspector No. 20326 and owner of Semenza Inspections, contact him at 361-676-1480 or gabe@semenzainspections.com.

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