Foundation repair companies commonly use phrases such as: “HUD tolerances for….”; “FHA tolerances for….”; or “Code tolerances for…” evaluating a slab on grade (concrete) foundation to determine if the foundation requires foundation repair. To our current knowledge, there is not published tolerance from HUD or the FHA that forces a homeowner into getting foundation repair. The third tolerance that is commonly quoted is the “Code” tolerance.
This “Code” may be assumed to mean the building code or the residential code. In either case, both the building code (better known as the International Building Code) and the residential code (better known as the International Residential Code) vaguely set a tolerance for foundation movement. The criterion that is commonly quoted in the industry of foundation repair is the L/240 or L/360. This may be interpreted to mean that over a distance (taken as inches) of X, a foundation that bends more than the ratio of L/240 or L/360, is assumed to not meet the “Code” criteria and hence the foundation should get foundation repair.
However, on the engineering side of the house, the deflection limited is used in the actual design of the foundation and is rarely used to evaluate the performance of the foundation. For instance, in forensic engineering we use the deflection limit to tell us how much load (weight) we can apply to a building given the construction of the foundation or the building. If we know how something is constructed then we can back-calculate the allowable load (weight) that can be applied. In foundation repair, the back-calculation is rarely, if ever, done. A structural engineer would be the most proficient in this calculation.
What does this mean to the average homeowner? well, if the person evaluating your home does not know how to back-calculate the allowable loads (weight) that the foundation can take once it is lifted, then they may actually cause the foundation to deflect or bend beyond the allowable limit that they just used to evaluate your foundation. Hence, the foundation repair may not really be a repair after all.
How often do commercial buildings get foundation repair?
The straight forward answer is very seldom. On the commercial side, apartment buildings probably see more foundation repair or leveling work than other commercial buildings. Why you may ask? Most of the apartment buildings that we have seen have severe plumbing and drainage issues that lifts and bends foundations. These are similar issues that a home with foundation problems has.
Structural engineers for commercial buildings typically will not consider lifting a building or doing foundation repair using a non engineered system, like concrete pressed piles. The reason is obvious; most concrete pressed piles that are installed by foundation repair companies are not engineered so the construction of the concrete pressed pile that will support your investment is wagered on a long list of factors that are not known.
A common overseen factor in concrete pressed piles is the safety factor that the building code states a piles or foundation should meet. The equations, mechanics, theories, and case studies for foundations do not change between commercial and residential buildings. The actual foundation has no idea if it is a commercial or residential building. The foundation simply reacts to what supports it, whether it is moving soils or a non-engineered concrete pressed pile foundation “repair” system.
However, it you lift (“repair”) the foundation then the foundation system for the building has drastically changed which may damage the actual building. We understand that there may be reasons to lift a foundation; however, lifting a foundation with a non-engineered system the follows the recommendations from a non-structural engineer may not be the best course of action for your investment.
Foundation Repair may classify your building as a “Dangerous Structure”
Foundation repair, as the name implies, is intended to make a foundation safe or meet a Code requirement or even “repair” your foundation. As we have stated in other articles, the “Code” for foundations in most municipalities (Austin and San Antonio included) is the International Building Code. This code is enacted as the code through a city ordinance; hence it becomes a city law. Another code that is not well known but constantly enforced in San Antonio is the San Antonio Property Maintenance Code (SAPMC) (this code was adopted by the CoSA in an ordinance). This code outlines the standard that the City of San Antonio uses to determine if a home owner is properly maintaining their building (commercial or residential). Section 108.1.1, Unsafe Structures, of the SAPMC refers the reader to Chapter 6 of the City of San Antonio City Code for a definition of a dangerous structure. Chapter 6, Article VIII, Sec. 6-156, defines a dangerous building. In that definition, the City Code states that a building may be deemed a dangerous building if:
- The stress in any material, member or portion thereof, is more than 1.5 times the allowable stress or stresses allowed by the Building Code;
- The building , or any portion of the building, is likely to partially or completely fail from the removal, movement or instability of any portion of the ground;
- A vertical structural member leans or buckles to such an extent that a plumb line passing through the center of gravity falls outside of the middle third;
- A building or structure has been constructed, exists, or is maintained in violation of the city’s minimum housing standards or technical building codes (IBC and IRC).
Read our code review article on Foundation Repair San Antonio and Foundation Repair Austin relating to concrete pressed piles. Foundation repair using concrete pressed piles is a system that consists of individual concrete cylinders that are hydraulically pressed in the soil to some depth that provides the foundation repair company with some capacity to lift your building. The system is seldom, if ever, actually designed by an engineer. An engineer might inspect the installation of the concrete pressed pile or tell the foundation repair companies where to put the concrete pressed pile but most concrete pressed piles used for foundation repair are not actually designed by an engineer so the code review and pile analysis may not happen.
If a structural engineer does not actually design the concrete pressed pile used in foundation repair then the criteria of item one mentioned above is not known, hence it is not met; the concrete pressed pile system will most likely be a stacked system that is highly susceptible to instability from soil movement, hence item two is not met; foundation repair companies seldom do soil analysis nor can they control the plumbness of the concrete pressed piles as it is pressed into the soil so item three is not guaranteed and is not met; and concrete pressed piles do not meet the International Building Code (see our article that reviews concrete pressed piles with Code requirements) so item four is not met. In conclusion, allowing your building to get foundation repair with concrete pressed piles may cause your home to be deemed a dangerous structure as defined by the City of San Antonio Property Maintenance Code.
Get a Engineering Company whose engineers are actually licensed to practice structural engineering, Such as A-1 Engineering.