A home’s foundation is so important that it’s even mentioned in the Bible—“the wise man builds on solid rock, the fool on sand.” But since foundations are mostly out of sight, it’s all too easy to forget the many structures holding our houses up. Bottom Line Personal asked home-improvement expert Danny Lipford what you need to know about your home’s foundation and how to correct any problems when they appear.

What Is the Foundation?

The foundation of your house is the fixed, solid (usually concrete) structure on which the building sits. Some very old homes will have only bricks stacked together. Rarely but occasionally, ­pilings are used. The foundation is not the planks and joists that comprise the lowest layer of the wood construction, but the stony support on which they rest.

Types of foundations. Thanks to local geography and building styles, there’s no single type of foundation that’s universal across the country. Here are the most common categories…

Concrete slab. You’ll usually find this in the South, especially in coastal areas where the water table is too high to make basements practical. It’s also the cheapest form of foundation when you are considering building a house. When a contractor builds a ­concrete-slab foundation, first the ground is graded, next the water and sewage lines are installed, and finally a four-to-eight-inch concrete slab is poured (reinforced with mesh and rebar), on top of which the house is built. There is no access beneath the home.

Basement foundations. More common in the Northeast, basement foundations consist of a bottom layer of horizontal concrete footings lining the perimeter of the building’s footprint, on top of which sits a poured-concrete (or cinder-block) wall, with a concrete floor across the base. The building rests on the wall. Basements usually are dug to eight feet beneath the building, which gives the foundation the added structural integrity of extending beneath the frost line. Basement foundations provide ventilation beneath the home, extra living space and easy access to utilities.

Crawl spaces. Most crawl spaces use concrete pillars around the perimeter to support the home. Sometimes the ­pillars are connected by a concrete-block “stem wall.” Unlike basements, crawl spaces are only two to four feet high, offering no additional living space. They’re often used when the ground is too rocky or hard for deep digging and keep the building up off the wet ground as well as providing ventilation under the house. It also is very common to run ductwork and place heating systems horizontally in crawl spaces.

Pier-and-beam foundations. If you’ve ever visited a beach community, you’ve likely seen homes set high on piers. Those foundations consist of a concrete disk or square pad set down into the earth and connected to a 10-by-10-foot or 10-by-12-foot piling that’s fastened to the house’s footing above. The foundation rests on compacted soil and sometimes compacted gravel or stone. The foundation footers usually have several pieces of steel rebar included for extra support. These foundations are designed to elevate the home clear of floodwater. Pier-and-beam is expensive but sturdy, and under-house access can be enough to park a car.

The above are the most basic types of foundations—there are variations and hybrids used by builders to accommodate terrain features and architectural styles.

Avoiding Problems

If any part of your foundation fails, you’ll encounter structural problems impacting the entire home, which will sag above the damaged section of foundation. Signs that your house may not be sitting level on its foundation: Doors that begin to stick…windows that jam…floors that are no longer level…cracks where the walls and ceiling meet…or dishes that clatter in the china cabinet when you walk across the floor.

The best way to avoid such problems is to keep water—the absolute worst enemy of foundations—away from the building. Water can wear away concrete over time…its freezing and thawing can put crack-forming pressure against walls…and it can wash away the ground beneath the foundation.

To keep water away from the foundation: Make sure you have a clean, well-functioning roof gutter system. Clean your gutters at least twice a year to ensure that the downspouts aren’t clogged. Your gutters should collect all the rainwater from your roof and empty it through downspouts that deposit the deluge on a slope at least 10 feet away from the building. (If your downspouts aren’t routing water far enough away from the foundation, installing extenders is an easy, inexpensive DIY job). Repair or replace gutters that are no longer working as soon as possible. Procrastinating almost guarantees that you’ll be adding in the cost of foundation repair.

During big rain events, check your lawn for pooling close to the house—if your lot is poorly graded and ­groundwater drains down toward the foundation, you will have problems. Small pools can be filled with shovels full of dirt, but major grading issues will require heavy equipment.

If you have a basement: Consider installing a sump pump to remove any water that pools on the concrete floor. It can damage your foundation if not pumped out. Sump pumps normally reside inside cylindrical pits dug into the lowest part of the basement. Professional installers cut through the basement floor where they intersect the walls and install perforated PVC pipe that collects water and feeds it to the sump-pump pit. The submersible sump pump is connected to a power source, and an output pipe with a check valve sends water out of the basement and into a nearby yard. The yard usually requires a catchment of crushed stone covered by soil.

What Can Go Wrong

On the upside, it’s rare that an entire foundation needs to be repaired or replaced—usually problems occur at specific pillars or sections of wall. But on the downside—these repairs typically cost between $1,500 and $2,500.

Concrete will just about always crack, but not all cracks are created equal. A crack that obviously follows the mortar between concrete blocks may look frightening, but it’s a very minor issue. You should worry more about a crack that ignores the mortar joints and runs straight up a wall—get a structural engineer to look at that right away.

You’ll also want help if you spot a raised crack in a basement or crawl space wall. In other words, if you were to lay a ruler perpendicularly across the line of the crack, there would be space beneath one side of the ruler. That means you have movement…and a structural problem.

Another sign of serious trouble is a bulging foundation wall. A bulge means the bricks have loosened and the house is squeezing down, causing the foundation to balloon or mushroom.

Sometimes water ends up channeling beneath the foundation, washing away the compacted soil, causing the foundation—and the house—to drop. This, too, is an uh-oh. In most cases, cracks will form on walls, both interior and exterior. These cracks indicate that settling is occurring.

Judging the urgency of foundation problems can be tricky. Sometimes they pop up overnight, in which case you should tend to them right away. Other problems take decades to develop and may not be as urgent. General rule: If something’s wrong with your foundation, get it taken care of as soon as you can.

How to Get It Fixed

Most homeowners lack the training and tools to do their own foundation repairs. Sometimes people who notice a sagging floor get beneath the building with a house jack to try to lift the joists back up to level. And sometimes that works—but oftentimes it makes things worse and ignores the real problem, and, given the enormous forces involved, it’s just not safe.

But don’t run to the phone and call a foundation specialist. Of course, there are good ones out there, but too many resort to scare tactics to get you to sign off on big, costly jobs. Instead, find an independent structural engineer, one who routinely works in residential ­scenarios, to do an evaluation. To locate a structural engineer: Call your local homebuilders’ association, and ask for a list of its members who are engineers. Or ask realtors or individual homebuilders—you’ll start to hear the same names coming up. Once the engineer has looked at your problem and made some recommendations, you can go to a foundation specialist armed with the engineer’s report. That’s the best way to avoid being taken advantage of.

The repair itself will depend on the specific foundation problem. But generally speaking, a specialist will use 20-ton house jacks to hold up the building while replacing—or sometimes supplementing—damaged pillars, foundation wall sections or parts of the slab. Depending on the extent of the damage, the job may entail some excavation work or controlled demolition of part of the foundation or even part of the house.

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