Foundations
The foundation of a building is the part that sits directly on the supporting soil. The purpose of a foundation is to support and evenly distribute all loads to the soil it rests on. The most durable and common material used for foundations is concrete. Concrete is a mixture of cement, aggregate, and water. The cement alone consists of a combination of lime plus silica, alumina and iron oxide.
The nature of concrete causes it to harden, and when it does, small surface cracks may develop. This is a natural process and is nothing to be concerned about. Bear in mind, concrete will often develop cracks, which does not necessarily mean it needs repair.
Today, the most common type of foundation found in the Houston area is the concrete slab-on-grade (usually referred as a "slab"). Concrete has great compressive strength, but little tensile strength (the inability to resist tension or stretching), which is why reinforcing steel (usually called rebar) is necessary. Post-tension cables are another type of reinforcement that is used in residential foundations. These foundations use steel cables that are laid through the form boards where the concrete slab is to be poured. Once the concrete has set, a truck with a hydraulic jack stretches the cable to provide tension. Because tension is applied after the concrete has set, the foundation is said to be post-tensioned. To better understand this, imagine lifting several books together by pushing in on the sides. The post-tensioned system uses the same principal to hold the slab together.
The second type of foundation, pier and beam, consists of piers spaced evenly under the house to support the floors and building load. One major difference between the pier and beam and concrete slab foundations is that pier and beam foundations have a crawl space between the floor of the house and the soil the house is built over. There are vents in the outer foundation wall and it is important that these not be covered. If proper ventilation is not maintained, the floor framing and sub-floor can begin to rot.
In most areas of Houston you will find houses with some foundation movement. Generally, the reason for this is not poor construction, but poor maintenance. "How do I maintain a concrete slab?" you might ask. Good question! Let us explain why maintenance is necessary and then how you can maintain your foundation.
Factors Affecting Your Foundation
u Soils In most areas around Houston the soils are heavy clay. The heavy clay that causes the most foundation problems contains montmorillonite. Soil with a high percentage of montmorillonite can change in volume (increase or decrease) ten to fourteen times, with the addition or subtraction of water. What this means in plain language is, if the soil your home is built on is expansive clay it can expand and contract tremendously if moisture content is allowed to fluctuate. When the clay soil is increasing in volume it can exert a force of three to fifteen tons per square foot. Most houses only weigh 350 to 450 pounds per square foot; consequently, the volume change can move a house up and down easily. Some people ask us, "Is this the black clay that does this?" Yes and no, color is not a good indication of whether soil is expansive. Expansive soils can be red, black, gray or even orange.
u Moisture Content Now let’s get back to the subject of maintaining your foundation. Since the moisture content under and around the perimeter of your foundation determines foundation movement, it follows that you should maintain the moisture content as evenly as possible to minimize movement. "Why can't nature take care of this?" you may ask. Let me explain it this way. "If you lay a large board on the ground and leave it for a week or so, moisture will build up underneath it, because the moisture cannot evaporate into the air with the board on it" The same thing happens with a concrete slab foundation, only on a larger scale.
When hot, dry weather comes along, some of the moisture will evaporate from the soil around the perimeter of your foundation, causing the soil around the perimeter to dry and shrink away from the foundation. This allows more moisture to evaporate from under the edge of the foundation. At this point the dry soil under the edge of the foundation has lost its load-bearing capacity in comparison to the soil under the middle of the foundation and allows the edge of the foundation to sag. If the foundation slab is cracked, it may or may not warrant repairs. This judgment should be left in the hands of someone that is experienced in inspecting foundations, a structural engineer.
Hot, dry weather is one of the biggest reasons for changes in moisture content under and around your foundation, but it is not the only factor in our area. Two others are uneven watering around the perimeter of the foundation or yard, and removal of moisture from under your foundation by trees and shrubs.
"What can I do about such items?" you might ask. Lets look at each item:
u Uneven Watering: When watering the foundation or yard, always remember the important thing is to maintain an even amount of moisture under and around your foundation. Now, we don’t mean you should float your foundation; too much water is just as bad as not enough. The easiest way to maintain a constant amount of moisture under and around your foundation is with an automatic sprinkler system.
u Soaker Hoses: If you do not have an automatic sprinkler system, you can maintain your foundation with soaker hoses. These hoses are either flat with small holes in them, or are a black rubber "leaky hose", If you use a soaker hose you should be aware that timers are available to use with them and will greatly simplify their use. Pier and beam foundations should be treated the same as slab foundations, when concerning watering programs.
u Plants: Another problem you might experience concerns the vegetation and trees around or close to the foundation. Some trees and shrubs require large amounts of water, and they are not particular where they obtain it. An ideal moisture supply for trees and shrubs is under concrete slab foundations. If there is not an ample supply of moisture, the tree and shrub roots will pull moisture out from under your foundation, causing the soils to dry and shrink, allowing possible foundation problems.
Landscaping
If you are going to plant trees and shrubs around you new home, here are some guidelines: In Texas, shade trees should be primarily on the east, west and northwest sides of a house. Also, we encourage you to carefully select the type the tree being considered. Decide what you really want from this tree or shrub - shade, fall color, or just eye appeal. Do you need a deciduous tree to shade an outside air-conditioning unit in the summer, while letting sunlight through in the winter? Do you want a line of evergreens to provide a windbreak in the winter and privacy the rest of the year? Another factor to consider is maintenance. Are the trees or shrubs drought resistant, or will they require large amounts of water? Along with these considerations, you should also think about their location in relation to plumbing lines, power lines, and your foundation. If your house is close to other houses, you should consider your neighbors. Why develop a problem with a neighbor if you can avoid it? Landscaping can increase your property value and save on your energy cost if done properly.
Some trees that can cause more than their share of problems are weeping willows, cottonwood, and Mulberry. They have root systems that spread out extensively and can damage foundations or invade sewer lines. Some good trees, as far as their roots are concerned, are red oak and live oak.
Shrubbery can also cause problems. Certain types require large amounts of water, such as wax leaf ligustrum or red-tipped photinias. When planting shrubs or flowers never dig areas next to your foundation that will be lower than the rest of the yard. This can cause problems by trapping water next to your foundation. Another way water is trapped next to your foundation is by metal or concrete borders around flowerbeds. Always remember to provide good drainage away from your foundation. The soil should slope gently away from your foundation. Happiness is planning, planning, planning.
Drainage
In conjunction with a good watering program, it is absolutely necessary to have good drainage around your foundation.
Most new homes start out with good drainage, but as years go by, the drainage deteriorates. One reason for this is the settling of dirt around the foundation because of rainwater dripping off the roof. Most of the time this can be corrected with fill dirt, but not always, so please do not ask your inspector how to correct a poor drainage situation, (he is not a specialist in this field and every case is different).
Generally speaking, sand or sandy loam is not good fill dirt if mixed with heavy clay. The reason for this is that sand or sandy loam does not have good load-bearing capacities compared to clay soil. Sometimes re-grading around the foundation is necessary to correct a poor drainage situation. Poor drainage does not necessarily mean the foundation is damaged, or will be damaged in the immediate future. If the situation is not corrected, it may be many years before the foundation is damaged if ever. Every situation is different.
You should not have standing or ponding water next to your foundation. Three common reasons for too much water are poor drainage around the foundation, a malfunctioning automatic sprinkler system, and leaking plumbing under the foundation. Too much water around your foundation will cause the soil to lose its load bearing capacity and very possibly cause foundation problems.
Many times we see homes that have poor drainage because the lot the house is built on is flat. After talking to the owners we find that originally there were swales or sloping channels to help water drain away from the foundation. When the owners bought the house, they thought the yard would look better flat, or it would be easier to mow the grass, so they leveled it.
Warning: If you do level the yard, you may void any builder's warranty a new home has concerning drainage.
Automatic Sprinklers
If you have an automatic sprinkler system, bear in mind, you should check it every few weeks to make sure all stations are operating properly. We have found that sometimes a lawnmower, being run over or someone doing repair work will damage a sprinkler head. Most sprinkler systems are programmed to operate in the early morning hours (i.e., 3:30 AM - 5:30 AM), so they not interfere with other water use during the day. However, because of the programmed time, no one sees the system in operation and whether or not it is malfunctioning. Therefore, you should walk the system through the stations manually every few weeks to check it. An indication or "red flag" in this area would be a larger than usual water bill or water ponding in the yard.
Rain Gutters
If your new home has poor drainage and you do not have rain gutters, then you should consider installing them. Rain gutters and correction of poor drainage fall into the category of helping to maintain your foundation. Rain gutters can be a valuable part of your foundation maintenance program. You must remember they are like everything else and must be maintained. If you allow them to become clogged with leaves or debris, they can do more harm than good by dumping large amounts of water in areas where it is not wanted. We know cleaning leaves out of rain gutters is not everyone's favorite pastime, so we suggest screens over the gutters, which are manufactured for just this purpose. Also, no one likes moving downspout extensions every time they mow the grass; the good news is that there are some extensions made out of flexible hose with a steel spring inside them to solve the problem. The spring rolls the hose up when it isn't raining, but when it rains, the weight of the rain water it unrolls it.
Note: As inspectors, we do not have the right to suggest installing rain gutters because they do not fall into the category of something that is broken or not performing as intended.
| 
