As featured in Concrete Contractor magazine, Aug. 2015
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 that have been raised by this inquiry. First of all, any homeowner who begins inspecting the concrete work performed will have concerns when cracks present. While the two truths of concrete are quite well known in the construction industry:
- Concrete gets hard.
- Concrete cracks.
The 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 the 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 common concern that presents during the final stages of the foundation work, and unfortunately all to often before the beginning stages of the above-grade structure work, has been identified. 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-0021. 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 a majority of the residential foundations, echoes the position of the IRC by stating:
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 exist so that the concrete wall performs like a beam and not a cantilever. The difference in performance or applied force can be quite 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 where problems have been created from backfilling with no top connection to validate this code position.
When a concern for movement in a foundation wall exists, however, caution should still be taken to not assume backfilling has cracked or pushed the wall inward. Some basic questions must still be asked.
The first is whether horizontal reinforcement was placed continuous in the wall and does it meet the minimum code requirements? The purpose of the required horizontal reinforcement is to reduce the number and width of cracks resulting from shrinkage.