Pre-cast concrete foundations:

This article explains How to Inspect & Diagnose Problems in Pre-Cast Concrete (Modular) Foundations - pre-fab foundation wall sections such as pre-cast "superior wall" foundations, precast concrete walls, how they are placed, how pre-cast concrete foundation walls are sealed, footing alternatives for pre-cast or modular foundations, and concerns for proper caulking or sealing between precast concrete foundation or wall sections.

Inspecting Pre-Cast Concrete Foundation Walls

Examples of both acceptable and questionable structural details & other failures in Pre-Cast Concrete (Modular) Foundations

Pre-cast foundation walls such as the Superior Walls R-5 ™ or Xi ™ (extra insulation) systems provide sections of concrete foundation walls which are lifted into place and bolted together, often sitting on a simple gravel footing-base, or properly installed, on crushed stone footings [2009 IRC section 403.4.1].

Most of the photographs of pre-cast concrete foundation walls shown here were taken more than a decade ago during construction of a Poughkeepsie, New York home. I must add that more than a decade later, by casual inspection from the street (owners haven't invited me in) I have not seen any evidence of movement in this structure even though the conditions photographed just above made me a bit nervous.

Superior Walls technical director Robert Hare points out that Superior Walls panels use specially formulated polyurethane sealant to seal these joints.

From some manufacturers, (not Superior Walls) the wall sections are sealed, typically with gaskets or caulk or both.

These are excellent building products with a proven track record, but as with any building material or procedure it's important that the precast concrete wall sections are properly transported, stored, installed, connected, and sealed, and that they are supported properly on footings or gravel properly prepared.

The defects we've observed were in pre-cast concrete foundation wall installation and did not involve evidence of structural failures.

• Incomplete sealing
  
  between foundation sections, leading to later basement leaks and water entry
• Poor modular foundation section alignment, 
  
  poor sealing between sections, particularly at building corners, resulting in foundation leakage
• Inadequate footing drains
  
   around the pre-cast concrete foundation (or none), and/or inadequate roof drainage system installation (gutters and leaders) resulting in flooding the foundation and water entry passing under the wall bottom and up over the basement slab at the slab/wall joint.
  
  Foundation leaks are not a product defect it's a poor installation practice. Some builders look at the pre-cast concrete wall sections as a waterproof material, forgetting that water can enter under a foundation or between improperly sealed foundation sections.

• Excessive spanning 
  
  of areas by pre-cast concrete foundation sections with no fill and no footing at all (shown in photo above) may lead to future water entry, floor slab settlement, or in severe cases, foundation movement. Spans over five feet would violate a Superior Walls guideline and other spans may be improper depending on the product and the engineering design for the project.
  
  Clarification from Superior Walls,
  Builder Guideline Booklet MAN 42-9000(June 2010) page 11 Figure 4 indicates that the maximum allowable over dig for a Superior Walls product is 5’-0”.  Inspectors observing large open spans of foundation walls should refer their clients to the original project engineer and the engineering drawings to check compliance.
  
  Note:  Superior Walls of America considers quality installations very important to our process, that is why every Superior Walls project is installed by a trained certified installer and Superior Walls panels are not by the builder or general contractor.

Note: the "floating" foundation wall shown above is supported at its left-end by a bracket set into the structural foundation wall of this Poughkeepsie home. The more-shallow right-hand wall was selected to be deep enough to be below the frost line and marks the entry to a garage.

I doubt that the design engineers consider this construction anything but fine. However soft backfill below the garage slab and entry may lead to later settlement problems in the driveway or garage floor.

• Basement water entry and leak problems
  
  require adaptation of common internal trench and drain systems, as cutting the slab to excavate for an internal drainage trench exposes the gravel footings. Inspectors should look closely at the connections and sealant between wall sections and look for evidence of leakage.
  
  While some manufacturers do not require sealing the inside bottom of the footer beam, as we note below, inspectors of existing structures are certainly expected to examine all foundation areas, corners, joints, footings, for indications of a history of water entry.
  
  Clarification from Superior Walls:
  
  It is certainly important that the joints are sealed properly to prevent possible water leaks.  However, when sealing Superior Walls panels it is not necessary to seal the inside bottom of the “Footer Beam”. 
  
  Therefore, we believe the picture that depicts the sealant not being  applied to the vertical section of the footer beam is not  a good example of “Incomplete Sealing”.

• Inadequate or omission of connections
  
  between pre-cast concrete foundation sections.
  
  Check closely at corners for bolts, connections & gaskets or sealant. Above our photo shows the connecting bolts and sealant at the corner intersection of two pre-cast concrete foundation wall sections. This connection can not be seen if the inspection is not performed before sill plates are set in place. However you may still note bolts at the corner bottom - shown below.

• Special basement waterproofing system details
  
  are needed if a basement de-watering system is installed after construction of a building with precast concrete foundations or walls.
  
  Foundation waterproofing companies such as B-Dri ™ who are asked to address water entry in homes built with these systems have to use modified intercept drain materials because the absence of poured footings under the walls gives less depth for an in-basement trench.
• Buried site debris:
  
  aside from being sloppy, lazy or offensive efforts to save a moment's work or a dollar of construction debris disposal, burying junk along the foundation before backfill invites later damage and water entry.

Reputable manufacturers of precast foundation wall products, including Superior Walls of America, supply their customers with site prep and construction details and that these are a great resource for inspectors. 

Superior Walls provides these details in Builder Guideline Booklet MAN 42-9000 [local copy] which is available on-line, free of charge.  This booklet includes a series of checklists, including one for Code Inspectors.

Watch out: As we also warn at WOOD FOUNDATION DEFECTS, a novice inspector may have trouble distinguishing between a completely-wood foundation and a pre-cast concrete foundation wall such as the structure shown above. If the sills and studs in this wall are concrete then it's almost certainly a pre-cast concrete foundation even though you may see plywood or OSB on the inside surface of the foundation cavity wall.

Pre-Fab Foundation Research & Sources

• Birkeland PW, Birkeland HW. Connections in precast concrete construction. InACI Journal Proceedings 1966 Mar 1 (Vol. 63, No. 3). ACI.
• Cajka R, Burkovic K, Buchta V. Foundation slab in interaction with subsoil. InAdvanced Materials Research 2014 Feb 6 (Vol. 838, pp. 375-380).
• Dickens HB. Trends in Canadian house production. [PDF] NRC Publications Archive, National Research Council Canada, (1968), NRC Publications Record / Notice d'Archives des publications de CNRC, source: Contact us / Contactez nous: nparc.cisti@nrc-cnrc.gc.ca. - retrieved 2015/12/09
• Dunkley D. Prefab shear walls. Journal of Light Construction. Dec. 1999 Dec.
• Elliott K. Precast concrete structures. Elsevier; 2002 Apr 17.
• Filiatrault A, Stieda CK. Seismic weaknesses of some residential wood framed buildings: confirmations from the 1994 Northridge earthquake. Canadian Journal of Civil Engineering. 1995 Apr 1;22(2):403-14.
• Freedman S. Loadbearing Architectural Precast Concrete Wall Panels. PCI journal. 1999 Sep 1;44(5):92-115.
  
  Abstract:
  Architectural precast concrete wall panels that act as loadbearing elements in a building are both a structurally efficient and economical means of transferring floor and roof loads through the structure and into the foundation. In many cases, this integration can also simplify construction and reduce costs.
  
  This article presents the m a ny benef its that can be derived from using loadbearing architectural precast concrete walls in buildings. Discussed herein are the various shapes and sizes of wall panels, major design considerations, and when loadbearing or shear wall units should be the first design choice.
  
  The role of connections, shear walls, and the use of precast concrete as forms for cast-in-place concrete is explained. In general, the design methods and techniques presented in this article apply to buildings in both seismic and non-seismic areas. The latter part of this article shows how these design principles can be applied in practice in a variety of buildings.
  
  These examples illustrate the use of window wall panels, spandrels, and solid or sandwich wall panels as the loadbearing wall members. When all the advantages of using arc h itectural precast concrete as loadbearing walls are added up, it makes good sense to use this structural form in building applications.
• Glass J. The future for precast concrete in low-rise housing. Leicester: British Precast Concrete Federation; 2000.
• van Holst AF, Westerveld CJ. Corrosion of concrete foundations in potential acid sulphate soils and subsoils in The Netherlands. InAcid sulphate soils. Proc. Int. Symp. on acid sulphate soils, Wageningen, The Netherlands 1972 Aug (pp. 13-20).
• Iverson JK, Hawkins NM. Performance of Precast/Prestressed Building Structures During Northridge Earthquake. PCI journal. 1994 Apr;39(2).
• Kurama Y, Sause R, Pessiki S, Lu LW. Lateral load behavior and seismic design of unbonded post-tensioned precast concrete walls. ACI Structural Journal. 1999 Jul 1;96(4).
• Luo, Yupeng, David R. Riley, and Michael J. Horman. "Lean principles for pre-fabrication in green design-build (GDB) projects." (2005): 539.
• Noguchi M. The effect of the quality-oriented production approach on the delivery of prefabricated homes in Japan. Journal of Housing and the Built Environment. 2003 Dec 1;18(4):353-64.
• Perez FJ, Pessiki S, Sause R, Lu LW. Lateral load tests of unbonded post-tensioned precast concrete walls. ACI Special Publication. 2003 Feb 1;211.
• Perez FJ, Sause R, Pessiki S. Analytical and experimental lateral load behavior of unbonded posttensioned precast concrete walls. Journal of Structural Engineering. 2007 Nov;133(11):1531-40.
• Persson B. Sulphate resistance of self-compacting concrete. Cement and concrete research. 2003 Dec 31;33(12):1933-8.
• Rahman AM, Restrepo-Posada JI. Earthquake resistant precast concrete buildings: Seismic performance of cantilever walls prestressed using unbonded tendons.
• Rasmussen TV. Prefabricated Elements Used as Strip Foundation of Single-Family Housing. In Buildings X Conference, Thermal Performance of the Exterior Envelopes of Whole Buildings X 2007.
• Rasmussen TV. Prefabricated EPS Elements used as Strip Foundation of a SinglefamilyHouse with a Double Brick Wall. Nordic Journal of Building Physics: Acta Physica Aedificiorum. 2008.
  
  Abstract:
  A new prefabricated lightweight element was designed for a strip foundation that was demonstrated on site as the base of a single-family house with a double brick wall. The element was placed on a stable surface underneath the top soil layer, just 0.25 m underneath the finished ground surface.
  
  The prefabricated element was designed to fulfil the requirements of low energy consumption required by the new Danish Building Regulations. The base of the house was cast in one working operation and completed within two working days. The element, made of expanded polystyrene, was designed to be handled on site by one man.
  
  A non-freezing ground was established by using outer insulation located at the outer plinth. Temperatures were measured at measurement points located at the outer plinth and onwards from these points underneath the building. In addition the soil temperature, the temperature within the concrete floor slab and indoor and outdoor temperatures and relative humidity were measured.
• Yee AA, Eng PH. Social and environmental benefits of precast concrete technology. PCI journal. 2001 May 1;46(3):14-9.
• Wraber I. Comparative study of Danish prefab houses made of wood. In6th Nordic Conference on Construction Economics and Organisation 2011 Sep 3 (pp. 441-452).
• Zal FH, Cox K. Pre. Fab: Myth, Hype+ Reality. InWood Structures Symposium 2009 Jul 7 (p. 15).

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Continue reading at CONCRETE SLAB CRACK EVALUATION or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

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