Some inspectors, engineers and foundation leveling companies use the elevation readings of the surface of a foundation to “determine” if a foundation has suffered differential movements or if a foundation needs “leveling”. A reading of the elevations of the surface of a foundation does not determine if the foundation has moved differentially. “Movement” is a function of time.
Movement is a change is position over a change in time. The taking of the elevations of the surface of the foundation can only define the configuration of the foundation at the time the readings were taken. The only way anyone can convince that your foundation has moved differentially based on a single set of elevation readings is if that person can convince you that the foundation of the structure was completely “flat” when the foundation was constructed.
No foundation is completely “flat” when it is constructed. If you don’t want to take my word for that just drive through any new subdivision after it rains and note that water stands on different areas of the foundation. That means that the foundation cannot be “flat” or “level”. It is true that flooring companies are supposed to cosmetically “level” the surface of the foundation before installing the floor covering materials but, that just really doesn’t happen.
If you want to determine if your foundation is moving differentially you will never to have the elevations of the foundation surfaces taken on more than one occasion over a period of time. You should wait until the weather conditions change. For example, if the weather has been dry, you should wait until after the ground is wet from several rains. This will give you the best chance for the changes in the elevations of the foundation to occur, if your foundation is moving differentially.
You should also know that the instruments used commonly by most inspectors, engineers and foundation leveling contractors are not all that accurate, that they require calibration fairly often and/or that they require some skill in use. Elevation readings should be taken in areas out of normal walking areas and the location of each reading should be taken in a place that can be fairly easily determined so that the elevation readings are taken at the same spot each time. The experts in measuring elevations are land surveyors. If you really want good elevation readings on the surfaces of your foundation, you should employ a land surveyor to take the elevation readings.
Generally, if the foundation of a structure is in need of leveling, you don’t need a professional to tell you that the foundation needs leveling. You will know it because you are walking up and down hill, your coffee cup won’t stay on the breakfast table, you keep rolling out of bed or the neighborhood kids skate board in your living room. If someone has to go to the extent to use measurements to determine that differences exist in the surface elevations of the foundation and you cannot feel the differences in the elevations as you walk through the house, what difference will “leveling” the foundation make?
Many “professionals” are of the opinion that all cracks in wall covering materials, out of square door frames, out of square windows, etc. are caused by differential foundation movements. In my experience with foundations, which spans over 40 years, only a small percentage of the wall cracks found in structures are caused by differential foundation movements. Most cracks, out of square door and window frames are caused by structural framing problems. But framing problems are harder to find, to understand and to explain to clients than it is to just assume that all problems are caused by differential foundation movements.
The performance of a foundation can only be determined during a real estate inspection or during a single inspection of a foundation by observing the performance of the superstructure and by observing the slopes in the surface of the foundation. If the foundation is not noticeably sloping and there are cracks in the wall covering materials, out of square door frames, out of square window frames, etc. then you should suspect that the problem lies in the framing. If the flooring of the second story sags and the surface of the foundation on the first story is relatively “flat”, you should suspect a defect or defects in the wall and second story floor framing system.
Differential foundation movements, unless extreme, do little actual damage to the framing of a house. After all, how many houses have you seen fall down from differential foundation movements? You should also understand that foundations were not designed to be “leveled”. “Leveling” of a foundation should only be performed when other means of controlling actual differential foundation movements fail and the slopes in the surface of the foundation are so severe that living in the house becomes uncomfortable