Technical Questions

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Tolerances for floors supporting operable partitions

Q. On a multi-story office building project using shored construction, we met the elevated floors’ specified flatness and levelness (FF/FL) of 25/20. But the architect has complained that installing floor guides for an operable partition required grinding and self-leveling topping. Is there an ACI tolerance for installing floors that receive operable partitions?


A. No; according to Section 4.4.1 of ACI 117, you were responsible for placing the shored suspended slabs within an overall elevation envelope of ±3/4 in. (±19 mm), along with meeting localized surface profile tolerances (peaks and valleys) controlled by the FF/FL specification. You met the specification. Unfortunately, the design team failed to coordinate the design and detailing of the slab and moveable partitions, as they set inadequate floor tolerance requirements and did not consider impact of slab deflections on this type of system.

Your project’s partition system is suspended from an overhead track and guided on a floor track. Installation of the partition’s long, flat, floor track required grinding and filling of the slab’s peaks and valleys. Although Section 4.4.2 of ACI 117.1R provides recommendations for establishing tolerance compatibility for installation of interior partitions, it doesn’t cover movable partitions.

However, ASTM E557, “Standard Guide for Architectural Design and Installation Practices for Sound Isolation between Spaces Separated by Operable Partitions,” provides recommendations that should have been considered, including:

  • “The floor immediately under the partition should not vary from a smooth level surface by more than ±1⁄8 in. (±3.2 mm) in 12 ft (3.7 m) non-accumulative. A steel member, such as a standard terrazzo strip, can be placed in a concrete floor to ensure this accuracy. Test Methods E1155 and E1155M are test methods for measuring floor flatness and levelness.” (Section 5.3.3); and
  • “The weight of the operable partition, in addition to all dead loads, should be taken into consideration when designing the supporting member. Deflection under maximum anticipated load should be no more than 1⁄8 in. (3.2 mm) per 12 ft (3.658 m) of opening width. If greater deflection is anticipated, either a structural member independent of the roof structure should be installed to support the operable partition, or an operable partition with bottom seals designed to accommodate the larger deflection should be specified.” (Section 5.5).

These recommendations explain your installation difficulties. A 1/8 in. gap under a 12 ft straightedge indicates an FF greater than 50. For a typical 36 ft span, a deflection limitation of 1/8 in. per 12 ft is roughly L/2400, where L is the span length. Designers typically use deflection limits ranging from L/480 to L/240, so it’s clear that ASTM E557 recommends some very specific and very high quality flatness and defection limits for operable partitions. These limits are far more stringent than the specified requirements for your project.

While ACI doesn’t provide a tolerance for installing floors that receive operable partitions, ACI documents do indicate that the architect is complaining to the wrong party. As stated in ACI 347R, Section 5.3.1: “The engineer/architect should be responsible for coordinating the tolerances for concrete work with the tolerance requirements of other trades whose work adjoins the concrete construction.” And, as stated in ACI 132R, Section 5.5: “The licensed design professional is responsible for accommodating individual material, product, and element tolerances at their interface with concrete construction to ensure tolerance compatibility.” To help avoid such problems in future projects, inquire about special material, product, and element (including operable partitions) tolerance in the bid or preconstruction phase.


References: ACI 117.1R; ACI 132R; ACI 347R; ASTM E1155; ASTM E557

Topics in Concrete: Tolerance, Concrete; Slab, Concrete

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