That Sinking Feeling : Small Cracks May Signal Big Trouble With Home’s Base

Bill and Greta Johnson never thought much about the little cracks around the door and windows in one of the bedrooms in their home.

But, when the Fullerton couple went to sell their home last year, an inspection discovered that the foundation below the bedroom was sinking. It was a problem that cost the Johnsons nearly $3,000 to repair in order to complete the sale of the house.

“I had been told that the house was just normally settling and that I should just repair the cracks in the plaster,” Bill Johnson says. “But when they pulled up the carpeting in the room they found some big cracks in the concrete subfloor that had to be dug out and worked on.”

The Johnsons’ foundation problem--and the way it was discovered--is not unusual in Orange County.

Subsidence, or the sinking of a home into the earth, keeps foundation contractors in the area very busy. “The clay soil in Southern California makes homes vulnerable to subsidence,” says Paul McGrath of White Foundation Contractors, a Van Nuys firm that has worked on many Orange County homes. “Many people discover they have a problem after the home is inspected before it’s sold, which is very inconvenient.”

Clay soil expands during the rainy season, but as it dries out in summer, the soil contracts and can bring a foundation down with it.

“During the drought a lot of people noticed foundation problems,” says Tallas Margrave of Western Piering, a foundation contractor in Anaheim Hills. “But when it started raining again and the ground became soaked, the earth swelled back up. The cracks people noticed became smaller, but they never completely closed up.”

An integral part of building a home is compacting the soil underneath, which limits the amount of foundation movement. “Much of the foundation problems we have are caused by improper compaction,” McGrath says. “During the building boom of the ‘50s and ‘60s, slabs as thin as two inches may have been poured onto unstable soil without the use of steel reinforcement. These mistakes keep people like us in business.”

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An Irvine homeowner who prefers anonymity because he’s in the midst of a dispute with his insurance company said he noticed cracking around the doors and windows toward the back of his house after last year’s Northridge earthquake. He saw that the cracks were expanding and contracting with the spring rains, and an engineer found a spot in the slab foundation near the cracking that dipped almost 1 1/2 inches.

“Their recommendation was to improve drainage and cover the areas where water could get to the foundation,” he says. “But I’m not sure what good that’s going to do me now.”

As with most homeowners in his position, the bad news of foundation problems was not mitigated with a call to his insurance company. As a rule, homeowner’s policies don’t cover repairs when a house is damaged due to subsidence or landslide.

Coverage is available, but at a price higher than most would be willing to pay.

“I found that a policy to cover a $250,000 home for subsidence would be approximately $30,000 per year,” Margrave says. “That’s why no one has coverage.”

Meanwhile, the cost of a foundation repair can be staggering.

Epoxy injections to fill minor cracks start at around $25 per linear foot, and the total replacement of a foundation can be $1,000 for every square foot of floor space. A minor piering job can start at $3,000.

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Experts agree that natural settling occurs for any foundation, and it would be hard not to find a concrete slab that hasn’t developed some small cracks over the years.

The good news is that much of Orange County is in a flat basin and free of problems that plague some other areas. The problems tend to occur if the topsoil hasn’t been compacted correctly or if the home has been built on an ancient stream bed or other undetected geological feature.

Most foundation problems occur when there is differential settlement--meaning that the ground under the house does not settle uniformly. That can occur where fill dirt has not been compacted properly, when a house is built on two different soil types or when drainage problems have affected the soil in one area and not another.

“It’s where one part of the house is moving at a different rate than another part,” McGrath says. “The cracks widen and become greater with the contraction and expansion of the soil.”

Homes in some areas are more vulnerable than others to foundation damage.

While most people dream of having a home with a view, hillside living often means carefully monitoring a foundation. “Grading always seems to be a problem for homes in the hills,” McGrath says. “Compaction is difficult during construction and that leads to problems with foundations and drainage.”

Before building in an area, a developer has a soil study done to look for any underlying problems. However, these may not tell the whole story, as was the case in recent years when several Anaheim Hills homes in one neighborhood suffered foundation damage.

“The soils report when they were built missed the fact that there was uncompacted alluvium ‘stream bed’ 150 feet below the surface,” Margrave says.

Hillside homes built with caissons or pilings to help support them run into similar problems. Technically, the pilings are supposed to be driven into bedrock.

However, getting down to the actual location of bedrock isn’t always feasible. “In Orange County, the bedrock layer is at least 6,000 feet down in most locations,” Margrave says. “Engineers usually specify that you need to reach ‘natural ground’ which can be 50 feet or more depending on where you’re located.”

On one home in San Juan Capistrano, Margrave found that entering the caisson-supported living room felt like he was walking downhill. “The caissons were mistakenly sunk only 26 feet, and the clay soil kept moving them. We ended up putting piers down 48 feet to stabilize the house.”

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Most foundation problems don’t require such a complicated repair. Cracks up to an inch wide can be filled with an epoxy that solidifies and reconnects two portions of the slab together; however depending on the crack and where it is, an engineer or contractor may recommend that the gap be broken out and that reinforced steel rods be anchored in before it’s sealed in new concrete.

How does one tell if one is in the midst of a foundation crisis? You may want to start by examining your doors and windows. “Look for diagonal cracking at the corners of door jambs and windows,” McGrath says. “That’s the first sign that the floor is moving.”

If you suddenly find that the doors and windows on one side of the house seem to be sticking, this could also be a sign of stress on the foundation. You don’t have to pull up your carpeting to check a concrete slab unless you suspect a problem, or if you can feel a crack underfoot.

Although you can’t re-compact the soil under your house to prevent foundation problems, there is one important precaution you can take: Direct water away from the foundation.

“Make sure your guttering is clean and working, and that water isn’t pooling around the house when it rains,” McGrath says.

Good drainage will keep the soil around the foundation from getting soaked, which will help reduce the amount of expansion and contraction going on beneath your house.

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Foundation Face Lift

It doesn’t take an earthquake to undermine the foundation of a home. In fact, recent heavy rains may have produced the right conditions for foundation cracks. But the damage won’t be seen until summer, when heat causes clay soil to contract and foundations to settle. Here is a primer on housing foundations, how to spot and repair cracks and how to prevent problems;

Building a Foundation

A foundation functions as both base and floor, carrying the weight of the house on solid ground. It provides a stable level base and counteracts any tendency of the ground to settle or heave. Typical foundation construction:

Causes of Cracking * Poor drainage * Unstable soil * Hillside construction * Inferior construction * Leaking pipes under foundation

What to look for * Cracks in driveway, porch or garage * Cracks in interior walls * Walls separating from floor or ceiling * Sinking foundation beneath fireplace * Exterior cracks in foundation, walls

Preventive Measures * Slope yard slightly away from house. * Install drain to reroute runoff in problem areas. * Install rain gutters and spouts with splash guards directed away from foundation. * Patch visible holes or cracks. * Check foundation and plumbing often for signs of leaking.

Soil Composition

Local soil is mostly clay. It expands when moistened and contracts when heat dries it. To avoid cracking, foundations must be able to withstand temperature changes and adapt to seasonal changes. Typical soil composition:

Top Soil: Dark gray clay (surface to two inches deep)

Clay: Black to 10 inches, turning olive (two to 15 inches)

Shale: Olive to 20 inches, turning yellow (15 to 25 inches)

Bedrock: Yellow to light brown.

Concrete Solutions

Repairing cracks can be expensive, especially if they go unnoticed for a long time. Costs can range from a few hundred dollars for crack repair to hundreds of thousands of dollars to replace caissons. Some common repair scenarios:

Reinforced Repair

Repairing cracks by filling them is appropriate only when there are few cracks. Small cracks can usually be filled by injecting epoxy. Larger, displaced cracks require a multi-step repair process. 1. Sides excavated to square off edges. 2. Steel reinforcement rods anchored into excavated crack; rods tied together. 3. Plastic sheeting, six to 10 millimeters, laid the length of crack to repel moisture. 4. Plastic covered with layer of sand; cement seals crack from sand to surface.

Underpinning 1. Soil excavated from sinking area. 2. Foundation leveled with jacks. 3. Jacks removed, excavated hole filled with cement.

Caissons Used to stabilize foundation of homes built on hillsides or in areas with soil problems. May be driven up to 60 feet deep. 1. Caissons (pilings) driven to bedrock. 2. Reinforced steel bar grid connects caissons and foundation. 3. Caissons and grid stabilized with concrete.

Sources: California State Licensing Board, White Foundation Contractors, South Tech, Methods and Materials of Residential Construction, Encyclopedia Britannica, Encyclopedia of What’s What; Researched by APRIL JACKSON / Los Angeles Times