Is it time for a floor elevation survey? Have you noticed a lot of cracking of the foundation or patios on your property? It could be related to ground or soil movement. When the ground under a property shifts, it can lead to cracked foundations, patio slabs and/or interior finishes such as drywall and tile. This can be especially true in places like Southern California where we have very adverse geology such as clays, loose sand and unstable hillsides. Add to this years of drought followed by an El Niño year, and ground movement is inevitable.
A floor elevation survey using a manometer can help an engineer better identify what areas under the foundation may be shifting. Identifying the problematic areas allows for solutions such as underpinning, ground modification and/or foundation repairs. In combination with visual observations by a qualified licensed engineer, floor elevation surveys are an excellent way of determining the performance of a structure. If you’re not familiar with a manometer, it’s a water level device that measures elevations to an accuracy of about +/- 0.1 inch. Often the floor level survey provides valuable data that points the engineer to problematic areas.
Floor elevation surveys, however, need to be interpreted by experienced engineers. If a house is tilted by several inches, did the high side of the house lift, or did the low side of the house settle? Or did a combination of the two happen? If the structure is supported on expansive and/or compressible fill soils, both uplift (due to expansive movement) and settlement (due to soil compression) can occur. Further analyses of the soil properties are required to properly interpret the measured floor elevations.
Some structure movements are cosmetic, and do not imperil the structural integrity of the property. When does the amount of foundation displacement result in movement that should be concerning? In general, if there is less than 1 inch movement over a horizontal distance of 20 feet, most timber framed commercial and residential structures are not adversely affected. If there is more than 1 inch of movement over 20 feet, however, structural damage can result. Masonry structures are more sensitive, thus smaller movements can result in structural distress. This damage can result in roof leaks, window and door operation difficulty, plumbing leaks, sewer problems, as well as weakening of the structure to withstand wind, seismic, and gravity loads.
Floor elevation surveys may also be used on properties located in high-risk areas by insurance companies. Sometimes the insurance company will require a floor elevation survey to determine insurance premiums for areas prone to landslides, earthquake and floods.
Have you had a floor elevation survey conducted on your property? Tell us your story about the experience in the comments section, below.