SINKHOLE ACTIVITY – VS – STRUCTURAL DAMAGE IN FLORIDA

Chapter 627 Florida Statutes (FS) contains the rules under which insurance companies write property insurance contracts. More specifically, Chapter 627.706 FS describes the rules for covering Sinkhole Insurance. In 2011, the Florida Legislature adopted rule changes that, among other things, attempted to better define “Structural Damage”. Up until that time, Engineers and Geologists charged with investigating claims alleging sinkhole activity relied on a relatively generic definition of structural damage commonly in use by Structural Engineers that determined the ability of structural members and systems to “support the loads that they were originally designed and constructed to support”. The courts, however, used a definition of structural damage that included “damage to a structure” which encapsulated many common causes for normal finish flaws and blemishes.

The definition of Structural Damage composed by the Florida Legislature and written into law is found in Chapter 627.706(2)(k) FS. That definition is as follows:

(k) “Structural Damage” means a covered building, regardless of the date of its construction, has experienced the following:

• Interior floor displacement or deflection in excess of acceptable variances as defined in ACI 117-90 or the Florida Building Code, which results in settlement-related damage to the interior such that the interior building structure or members become unfit for service or represents a safety hazard as defined within the Florida Building Code;
• Foundation displacement or deflection in excess of acceptable variances as defined in ACI 318-95 or the Florida Building Code, which results in settlement-related damage to the primary structural members or primary structural systems that prevents those members or systems from supporting the loads and forces they were designed to support to the extent that stresses in those primary structural members or primary structural systems exceeds one and one-third the nominal strength allowed under the Florida Building Code for new buildings of similar structure, purpose, or location;
• Damage that results in listing, leaning, or buckling of the exterior load-bearing walls or other vertical primary structural members to such an extent that a plumb line passing through the center of gravity does not fall inside the middle one-third of the base as defined within the Florida Building Code;
• Damage that results in the building, or any portion of the building containing primary structural members or primary structural systems, being significantly likely to imminently collapse because of the movement or instability of the ground within the influence zone of the supporting ground within the shear plane necessary for the purpose of supporting such building as defined within the Florida Building Code; or
• Damage occurring on or after October 15, 2005, that qualifies as “substantial structural damage” as defined in the Florida Building Code.

From a structural engineering standpoint, we are often called upon to address whether or not sinkhole activity, in and of itself, has either been identified or cannot be ruled out at depth on a subject property and is a direct and proximate cause of “structural damage”. While the expanded definition(s) of what constitutes structural damage in a given building are helpful, in my opinion there are cases when they are not. An example of just such a case is seen below:

This house was built in 2007 utilizing reinforced masonry construction standards. The foundation consists of a continuous reinforced concrete footing cast monolithically with the interior concrete floor slab. The exterior finish is painted stucco cladding with interior floor finishes being predominately large-format ceramic tiles. In late summer 2011 a small dropout occurred under a window on an exterior load-bearing perimeter wall of the residence. This was confirmed by a subsurface exploration program to be associated with sinkhole activity. The dimensions of the dropout were measured and found to expose approximately 7 feet of the footing and the cavity extended less than 3 feet under the concrete slab. At its greatest depth, the soil was approximately 6 inches below the bottom of the exposed footing. The dropout was investigated approximately 2 months after it was first observed by the homeowner. The investigating engineer recommended that the cavity be immediately filled with “flowable fill” (a high slump grout) to restore continuous bearing conditions for the footing, and that other stabilization measures be implemented “as soon as practicable”.

The above photograph was taken more than 2 years after the initial event occurred and, to date, no stabilization measures recommended by the investigating engineer have been implemented. The reason for the delay in implementation of stabilization is not important to this discussion. What is important to note is that while more than 2 years have elapsed, the in situ conditions have not changed. What is also important to note is that there has apparently been no movement or settlement of the foundation that has resulted in cracks being propagated into or through the neither stucco cladding, nor are there any cracks appearing on or in the large format ceramic tile on the interior above this location. What is also more remarkable is that this is occurring at a penetration in the exterior load-bearing wall (a window) which is a location that structural engineers colloquially refer to as, “a weak point in an otherwise perfectly good structural wall.” This is also not a low point on a relative elevation study done for the interior concrete floor slab. In fact, there is no evidence to even suggest that the structure has even reacted to a loss of support under a portion of the foundation.

“So”, one might ask, “which of the definitions has been met as sinkhole activity on the property seems apparent?” Clearly, No. 1 does not apply. Neither, does Nos. 3, 4, or 5; although, some might argue that No. 4, or parts thereof, perhaps might. Operative words in No. 4, such as “imminently” and “instability”, do not seem particularly applicable more than two years after the occurrence. Rule definition No. 2 seems the closest; however, again there is no evidence that foundation displacement or deflection in excess of acceptable variances is present. Does a sinkhole loss exist in this case?

What might be helpful is to clarify the definition of “structure” in the extant case such that the engineer can better differentiate between “Superstructure” and “Substructure”. Superstructure is commonly accepted to mean “the framing above the main supporting level or substructure, as a foundation wall”. Substructure is also commonly accepted to mean “the lower portion of a structure forming the foundation which supports the superstructure of a building”. In the case of a foundation such as found in the residence under consideration, it is designed and constructed to be continuously earth supported. If we include in the definition of substructure, for foundations intended to be continuously earth supported, surficial soils within the influence zone of the foundation then rule definition No. 2 would seem to apply as that part of the foundation is no longer functioning as intended and has failed even though displacement and settlement related damage to the superstructure are not evident. Thus, a sinkhole loss has occurred. A discussion on foundation stabilization for a case such as this will be left to another time.