Precast structures should be designed and detailed so that the complete structure will be safe, functional, aesthetically appealing, and economical. No structure is exactly level, plumb, straight, and true, so all construction and materials should be specified with tolerances limiting deviation from design values. These tolerances require monitoring to construct the structure as designed.

Tolerances are typically divided into three primary categories:

  • Component tolerances
  • Erection tolerances
  • Interfacing tolerances

Additional information concerning these tolerances, their relationships, and their application can be found in MNL 135, Tolerance Manual for Precast and Prestressed Concrete Construction. Tolerances for the design, manufacture, and installation of precast concrete components and fabricated embeds are contained in PCI 135, Specification for Tolerances of Precast Concrete.

PCI 135 was issued in 2025 and the tolerances in PCI 135 supersede those in MNL 135. Additional information about these changes can be found below.

Frequently Asked Questions (FAQ)

The title of PCI 135 is “Specification for Tolerances of Precast Concrete”. The document is a compilation of production and erection tolerances for precast concrete components and related products.

Both PCI 135 and MNL 135 are developed and published by the Precast/Prestressed Concrete Institute. Founded in 1954, the Precast/Prestressed Concrete Institute (PCI) is the technical institute and trade association for the precast, prestressed concrete structures industry. More information about PCI can be found on the PCI website (pci.org).

MNL 135 was last issued in 2000, so there was a need for the document to be reviewed and updated. The institute decided to issue the update as a standard and PCI’s ANSI process requires standards to be reviewed and updated every five years, thereby helping ensure that the document content remains current.

The Prestressed/Precast Concrete Institute is using the designation of “PCI” for documents written in standard code language, while “MNL” is used for QC manuals. The PCI 135 standard contains only mandatory language; commentary explaining the requirements has been added at the end of the document.

Both types of documents are developed by a PCI technical committee and then reviewed and approved by the responsible PCI Council and PCI’s Technical Activities Council. PCI specifications are developed following PCI’s ANSI-approved process, which also requires review by the PCI Standards Committee and posting of the document for public comment. During each step in the process, comments received must be reviewed by the committee/Councils, with responses prepared and approved.

  1. Section 1.2 Definitions provided are for specific terms as they are used within PCI 135
  2. Chapter 2 on “Project Responsibilities and Requirements”
  3. Chapter 3 “Fabricated embeds and erection hardware” were not in the previous MNL 135
  4. Chapter 4 “Production Tolerances”
    1. contains previous MNL 135 production component tolerances with a few added tolerance dimensions on some products and clarifications on others.
    2. added product tolerances:
      • 4.3.6 Precast concrete solid flat slabs
      • 4.4 Glass-fiber-reinforced concrete (GFRC)
    Chapter 5—"Erection Tolerances”
    1. added erection tolerances
      • 5.4 Glass-fiber-reinforced concrete (GFRC) erection tolerances.
      • 5.5 Connections and bearing.

MNL 135 is being revised as a resource document in nonstandard language to educate users who will reference PCI 135 prescriptive language denoting the dimensional tolerances associated with precast fabrication and erection. The PCI Tolerance Committee is currently balloting proposed changes to MNL 135. The goal is to publish the updated MNL 135 by the end of 2026.

PCI 135 was developed with added input from the precast industry through a public comment period and PCI 135 will have a mandatory review and update schedule as defined by the ANSI process.

In summary - PCI 135 is a standard accepted by industry and planned to be referenced by ACI in their tolerance document and is written in prescriptive (mandatory) language. MNL 135 is a resource document that goes into more depth about tolerances and how to understand and apply them.

MNL 116 and MNL 117 both reference MNL 135 for production tolerances. Addenda are currently being prepared to change the reference to PCI 135. These addenda are expected to be approved and released before 7/1/2026. Conformance to the tolerances by PCI-certified plants is expected beginning 1/1/2027. The upcoming edition of MNL 135 does not contain product and erection tolerances but instead references PCI 135 for these. MasterSpec will need to be updated so that the document reference is changed to PCI 135.

ACI 117, Specification for Tolerances for Concrete Construction and Materials. ACI 117 references ITG 7, Specification for tolerances for Precast Concrete. ACI is planning an update to ACI 117 that will reference PCI 135 and ITG 7 will no longer be an active document.

Overview of Changes to PCI 135-25 from MNL-135-00

  1. Standardized, Prescriptive Language: PCI 135 is a specification and written in ANSI standard prescriptive (mandatory) language. Commentary explaining the requirements has been added at the end of the document. MNL 135-00 includes a combination of prescriptive and non-mandatory language.
  2. Regular Review Cycle: As a PCI document conforming to the ANSI process, PCI 135 will be on a schedule for review and update every five years.
  3. Consolidation of Tolerances: All dimensional tolerance requirements for component production and erection has been moved from MNL 135 to PCI 135, along with information on interfacing tolerances.
  4. Updated Definitions: PCI 135 has an updated list of definitions.
  5. New Chapter on Hardware: Chapter 3 of PCI 135, “Fabricated embeds and erection hardware”, includes tolerances for products that were not in the previous MNL 135. The standard now includes tolerances for:
    1. Fabricated embed plates (Figure 3.3.1)
    2. Fabricated loose plates with hole or slot (Figure 3.3.2)
  6. Added Production Tolerances: Chapter 4 of PCI 135, “Production Tolerances”, has added production tolerances for the following components:
    1. Fabricated precast concrete solid flat slabs (Figure 4.3.6)
    2. Glass-fiber-reinforced concrete (GFRC) products (Figure 4.4.1)
  7. Added Erection Tolerances: Chapter 5 of PCI 135, “Erection Tolerances”, has been expanded to include new sections for:
    1. Glass-fiber-reinforced concrete (GFRC) products (Section 5.4).
    2. Connections and bearing (Section 5.5).
  8. New Appendix for Architectural Certification: An appendix was added, outlining the production and erection tolerances for architectural components for PCI architectural certification categories AA, AB, and AC.
  9. Broad Committee Review: Various PCI committees representing the different types of PCI components were consulted resulting in the clarification and update of tolerances within PCI 135.
  10. MNL 135 Repurposed: The next edition of MNL 135 is planned for publication in late 2026. MNL 135 is a resource manual that includes information to be used by the design team when considering project tolerances, background information for evaluating tolerances with examples, recommended sample forms, and typical tolerance related details, among other information. MNL 135 will reference PCI 135 for actual production and erection tolerances.

Questions concerning tolerances or the changes from MNL 135 to PCI 135 can be addressed to technical@pci.org.