Question: The foundation for my new home has one wall showing two vertical cracks and the top of the wall is not even with the base of the wall. I’m concerned the backfilling has pushed the wall in and the building inspector wants an engineer to certify the wall before the builder can proceed. What should I do? – Home Owner (Wisconsin)

Answer: The process of building a foundation for a home inevitably leads to the two most common issues, both of which have been raised in this inquiry. First, any homeowner who begins inspecting the concrete work performed will have concerns when cracks present. While the following facts about concrete are quite well known in the construction industry, it’s worth laying them out plainly:

1. Concrete gets hard.
2. Concrete cracks.

Yet, an owner is not prepared to consider this an acceptable explanation.

Cracking, by itself, should never be an immediate cause for concern. There are distinct characteristics of cracking that determine rather quickly whether a crack is problematic or simply a result of the drying and shrinkage process. More information on cracking can be obtained from our website in a free public download (http://bit.ly/aboutcracks).

However, in the case of this inquiry, another concern was identified, one that presented during the final stages of the foundation work—and, unfortunately all too often, this issue emerges before the beginning stages of the above-grade structure work. That is, the wall is out of plumb and backfilling has been completed. It must first be noted that the primary code references for residential foundation walls both state limitations for the backfilling operation. For a practical interpretation of the backfill process, the CFA provides a tech note on backfilling, TN-002.¹ The International Residential Code (2015) states:

R404.1.7 Backfill placement. Backfill shall not be placed against the wall until the wall has sufficient strength and has been anchored to the floor above, or has been sufficiently braced to prevent damage by the backfill.²

Furthermore, ACI 332, which provides a broad set of minimum prescriptive code requirements and the performance-based design for the majority of residential foundations, echoes the position of the IRC:

8.2.4 Lateral restraint. The equivalent fluid pressure of the backfill shall be determined, but in no case shall be taken as less than 30 psf/ft. The foundation walls shall be restrained top and bottom against lateral movement. The top and bottom restraint for the foundation wall shall be in place before the introduction of backfill against the foundation wall. Temporary lateral restraint shall be permitted.³

Both code references call attention to the same design assumption for foundation walls: a positive top and bottom connection exists so that the concrete wall performs like a beam and not a cantilever. The difference in behavior of these two wall conditions due to the applied force can be substantial. While it is true there are likely hundreds of thousands of successful constructions where a top connection (the first floor framing) or bracing was not installed prior to backfill, there are enough cases to validate this code position where problems emerged from backfilling without a top connection.

When someone is concerned about movement in a foundation wall, however, they should not immediately assume backfilling has cracked or pushed the wall inward. Some basic questions must first be asked.

First, was the horizontal reinforcement placed continuous in the wall, and does the reinforcement meet the minimum code requirements? The purpose of the horizontal reinforcement is to reduce the number and width of shrinkage cracks.

Second, is the wall bowed out of plane or leaning out of plane? This is an important condition to note. In order to determine the answer to this condition, a string line is the best method to test the position of the wall. A string should be drawn taught from bottom corner to bottom corner and from top corner to top corner. The string should be pulled taught as it approaches the wall so it can be determined if it touches a point near the wall’s center before getting to the corners. There are three potential outcomes from this test.

• String line is true at base of wall; string line at top of wall shows a bow. This is the case most likely to be of concern to an engineer, and if this is the result, it is best to engage in a discussion with the owner, designer and controlling contractor for the project, as applicable. With no bow at the base of the wall, the forms were set up true, and it may be assumed that the top of the wall corresponded to the base, since forms are rigid. The bow evidenced by the string is more likely to be a result of the backfill operation, and the wall’s stability is the next condition to investigate. An engineer should be involved at this stage. (It should be noted that insulated concrete form walls might vary from this assessment if they are plank or block style.)
• String line is bowed at base of wall; string line at top of wall shows a bow. This condition is a bit trickier and may still require an engineer’s assessment. Variation in the bow may still indicate influence by the backfilling operation. However, the bow in both the bottom and top of wall may also indicate a forming tolerance issue and forms that were not set completely straight. This is particular, and the fact that the footing connection provides restraint against bowing or movement further indicates that the wall was likely formed to that bowed shape.
• String line is true at base of wall; string line is true at top of wall. A true string line should be the first indication that a forming tolerance is at hand. Walls that are loaded dynamically and moved from their cast position will evidence stress. Stress is not applied uniformly and movement does not distribute force uniformly. The wall is confined at the corners where it has natural restraint and a much higher resistance to lateral displacement from soil loads. Therefore any movement leads to bowing along a longer section or cracking at or near the corners.

In the case of the project at hand, the contractor engaged the owner and demonstrated that a string line was true at both the top and bottom of the wall. The two cracks were spaced relatively evenly across the wall and were located on form joints, which indicates a pattern of shrinkage cracking. Yet, the top of the wall was out of plumb inward by 1.5 inches, indicating an issue for tolerances.

Any project should be approached with hopes for perfection, and yet construction involves a series of processes that requires allowance for conditions that are less than perfect. The CFA Standard⁴ offers the following when considering tolerances:

8.3 Foundation Tolerances – The wall should be considered within tolerance if the following conditions are met:

• The deviations did not cause the building to become structurally unstable.
• The deviations did not encroach on areas reserved for other work.
• The deviations did not severely impede other trades from doing their work.
• The deviations did not put the building out of compliance of the governing building code.
• The deviation or blemish did not contradict the specified class of architectural finish (unspecified class assumes “unfinished”).

The investigation of the project resulted in a decision that the foundation wall was formed with a bowing deviation along this particular wall. It was the only wall with such a remarked deviation. Determining if the deviation is within acceptable tolerance is the next consideration. There are three references that influence this determination, as the jurisdictional codes do not address tolerances. Those references are 2010 CFA Standard, ACI 117,⁵ and Residential Construction Performance Guidelines of the National Association of Homebuilders (NAHB). The particular tolerance for being out of plumb of a vertical plane varies greatly across these three industry references. The NAHB reference is the most directly applicable reference for both residential construction and understanding how something is deemed acceptable or not. This reference states:

2-13 – Concrete walls shall not be out of plumb by more than 1.5 inches in 8 feet when measured from the base to the top of the wall.⁶

Applying this reference and considering all conditions for this project. The homeowner, builder, and contractor should be having a conversation about how to complete the space for effective finishing of the basement. Concern for structural stability does not seem warranted, despite the builder proceeding with backfill ahead of top connection or temporary bracing.

Want to know more? Contact CFA Executive Director Jim Baty at 866-232-9255 or by email at jbaty@cfaconcretepros.org. The CFA is a national association with the mission to support the cast-in-place contractor as the recognized voice and authority for the residential concrete industry.

References:

1. Backfilling Foundation Walls (TN-002), published by the Concrete Foundations Association, 402 1st Ave SE, Mount Vernon, IA 52314 | Phone: 319-895-6940 | www.cfaconcretepros.org
2. 2015 International Residential Code® For One- and Two-Family Dwellings, published by the International Code Council, Inc., 4051 West Flossmoor Road, Country Club Hills, IL 60478-5795 | Phone: 888-422-7233 | www.iccsafe.org
3. Residential Code Requirements for Structural Concrete (ACI 332-14) and Commentary, published by the American Concrete Institute, 38800 Country Club Drive, Farmington Hills, MI 48331 | Phone: 248-848-3700 | www.concrete.org
4. 2010 CFA Standard, published by the Concrete Foundations Association, 402 1st Ave SE, Mount Vernon, IA 52314 | Phone: 319-895-6940 | www.cfaconcretepros.org
5. Specification for Tolerances for Concrete Construction and Materials (ACI 117-10) and Commentary, published by the American Concrete Institute, 38800 Country Club Drive, Farmington Hills, MI 48331 | Phone: 248-848-3700 | www.concrete.org
6. Residential Construction Performance Guidelines for Professional Builders & Remodelers, published by the National Association of Home Builders, National Housing Center, 1201 15th Street NW, Washington, DC 20005 | 800-368-5242 | www.nahb.org