Benson, AZ Foundation Investigation
Challenge
The owner of this Benson, AZ twin home reached out to us after noticing signs of a potential foundation problem. These symptoms included:
· Exterior concrete slab cracks
· Interior drywall cracks
· Interior wall separation
· Gaps in the interior baseboards.
Homeowner’s Concerns/Goals: The homeowner is concerned with the makeshift beam in the crawl space, cabinets leaning, and the kitchen wall.
An initial, Level A Foundation inspection concluded a Level B Foundation Investigation needs to be completed.
Purpose of the Investigation: The purpose of this report is to evaluate the foundation and the foundation conditions of this property, and to perform a manometer and foundation survey on the interior of the property.
Limitations: The purpose of this report is limited to documenting and addressing the areas of concern indicated by the customer related to potential foundation movements. Arizona Foundation Solutions uses a variety of tools such as manometer survey, observations by technicians with notes and photographs, and industry standards such as the Foundation Performance Association (FPA) “Guidelines for the Evaluation of Foundation Movement for Residential and Other Low-Rise Buildings” to determine if foundation movement has impacted the serviceability of the home. The term serviceability relates to items such as pinched doors and windows, cracks in drywall and slabs, cracks in exterior stucco and walls, and the like. Recommendations in this report are made to address and limit future issues related to serviceability and the customer’s concern.
Unless expressly stated in the Safety and Structural Concerns section of this report, nothing in this report should be interpreted as a determination of structural inadequacy, an occupancy issue, or a safety issue. This report offers no opinions as to the adequacy of the work of previous designers or contractors.
The extent and scope of this manometer and foundation survey and assessment are detailed as follows:
• Perform a manometer survey.
• Locate areas of potential foundation and floor movement if any.
• Visually inspect and record the interior and the exterior of the location.
• Evaluate any noted movement using industry consensus methods if any.
• Prepare a documented repair plan if needed.
Foundation Footprint: A drawing of the footprint of the first floor was created and is included in this report.
Exterior Inspection: The exterior of the location was visually inspected. Items such as foundation cracks, exterior wall cracks, improper grading, type of structure, poor drainage, gutters or no gutters, bowed retaining walls, large trees close to the foundation, and any type of obstructions that may or may not influence the repair process were noted and recorded.
Interior Inspection: The interior of the location was visually inspected. Items such as floor cracks, wall cracks, ceiling cracks, sloping floors, uneven countertops, doors and windows that are out of alignment, cracked window glass, and bowed walls were noted and recorded.
Manometer Survey: The manometer survey, also known as a floor survey, is a measurement of the differences in interior floor elevations. The flatness of the interior floor was measured using a highly accurate survey device known as a Manometer. The entire interior floor area was surveyed and the elevations were recorded. These data points were then entered into a computer program that provides a topographical map showing the high and low elevation contours of the floor surface. This topographical map shows where the foundation is no longer level and shows where support and stabilization are needed. The floor survey also demonstrates whether any floor slab heave or settlement exists.
After examining the home and performing the manometer survey, Arizona Foundation Solutions believes the home could be experiencing foundation settlement at the central portion of the home as shown by the damage (also known as Signs of Stress) and lower readings on the Topographical 2D Map. The drop-off in floor elevations on the topographical map is consistent with a foundation settlement pattern. Settlement can be caused by one or any combination of many factors including sub-grade saturation of moisture due to poor drainage, years of storm runoff, plumbing leaks, improper compaction, the lack of a proper foundation system, and/or (in most cases) natural earth movement.
An edge heave pattern is observed in the northern portion of the home as indicated by the higher elevation readings on the Topographical 3D Map. This phenomenon usually occurs in areas where structures are built on expansive clays. Moisture from one or any combination of the following: storm runoff, poor drainage around the foundation, plumbing leaks, and/or underground moisture sources will allow the moisture/vapor to accumulate underneath the foundation. The moisture then interacts with the clayey soils, causing them to swell. The clay soils take the path of least resistance and expand upwards and lift the foundation.
The Foundation Performance Association (FPA) “Guidelines for the Evaluation of Foundation Movement for Residential And Other Low-Rise Buildings” were adopted to correlate acceptable and unacceptable distress phenomena with actual survey elevations. Deflection and Tilt calculations were performed and compared to allowable values. For this engineered analysis, the deflection of the slab (L/420) was less than the allowable deflection limit of L/360. In addition, the tilt of the slab (0.2%) was less than the allowable tilt of 1.00%
While the tilt and deflection were less than the allowable limit, this is a general guide and the home is showing distress at areas indicating heave and areas indicating foundation settlement.
Solution
AZFS believes the best way to stabilize the support beams in the crawl space is with Smart Jacks. These are adjustable galvanized supports engineered to be placed under the sagging floors to help prevent settlement of the floor joist system. The Smart Jack sequence should start at approximately 2’ off each perimeter wall and should not be spaced more than 7’ on center (exact spacing to be determined after load-bearing calculations). An engineered push pier will be driven concentrically beneath the beam at each Smart Jack location to provide a footing for each Smart Jack. If for whatever reason the installation of concentric piers is not possible, a concrete footing of engineered size will be poured beneath the Smart Jack to distribute the load. The Smart Jacks will then be cut to size and set in place. Finally, the units will be adjusted to lift the sagging floors back to their best functioning point or the Highest Practical Maximum.
Arizona Foundation Solutions believes that the proper way to deal with edge heave is to first install piers to support the perimeter walls of the area that is experiencing edge heave. Under excavation will be performed in this area. This is where some of the heaving soils will be removed to create voids for future expansion. If possible the perimeter can be lowered to practical recovery. This will be determined by field conditions.
Since storm runoff is responsible for the majority of the moisture that pools next to the foundation, gutters need to be installed to prevent the storm runoff from increasing the amount of foundation movement. A proper gutter system should be installed to discharge the storm runoff a minimum of 10 feet, preferably 20 feet away from the foundation. We do not recommend installing gutters that discharge next to the foundation as this will only increase the probability of a foundation problem.
It is also beneficial to manage the moisture around your home using conventional means as outlined below:
• Hire a reputable plumbing leak detector and repair service to check both pressure and sewer lines, this is usually done for less than $500. If repairs are needed, they are usually not expensive.
• Make sure the grading of the terrain is sloped downwards at a 5% slope from the home at all areas of the perimeter.
• Stop irrigating plants that are near the foundation and make sure there is nothing trapping the moisture from flowing away from the home.
• When permanently stabilizing, lifting, and/or mitigating a foundation movement problem, AZFS recommends waiting AT LEAST 6 months before investing in cosmetic repairs.
Safety or Structural Concerns: None
Project Summary
Engineer: Néstor J. Brea
