Expansion and Control Joints
Donald E. Smith, CCS
March 2008Don Allen from the Steel Framing Alliance came up with this month’s question, which deals with the definitions of expansion joints and control joints. Another part of the question concerned the bridging of a control joint in a building with a drywall soffit. The crux of the problem seems to be that the contractor does not believe that bridging a control joint in an exterior concrete wall with cold formed steel framing will present a problem in the future. Let’s deal with the definitions first.
These definitions have been a contentious issue in past meetings of ASTM Committee C11, Gypsum and Related Building Materials and Systems. Currently there are three definitions in ASTM C11-07, Standard Terminology Relating to Gypsum and Related Building Materials and Systems, that come into play:
Building construction joint, n—a designed division of a building that allows movement of all component parts of the building, in any plane which may be caused by thermal, seismic, wind loading or any other force. The construction of the separation is accomplished by one of the following methods: (1) manufactured devices suitable for this application, or (2) by field fabrication of suitable materials. Control (expansion construction) joint, n—a designed separation in the system materials that allows for movement caused by expansion or contraction of the system. The construction of the separation is accomplished by one of the following methods: (1) manufactured devices suitable for this application, or (2) by field fabrication of suitable materials.
Expansion joint, n—see control (expansion contraction) joint.
At a recent ASTM meeting, C11 was successful in adopting new definitions for expansion joints and control joints for use in C1063, Standard Specification for Installation of Lathing and Furring to Receive Interior and Exterior Portland-Cement Based Plaster. These are the definitions as adopted:
Control joint, n—a joint that accommodates movement of plaster shrinkage and curing along predetermined, usually straight, lines.
Expansion joint, n—a joint that accommodates movement beyond plaster shrinkage and curing.
Note: For design consideration of control and expansion joints, see ASTM C926, Section A126.96.36.199.
The definitions in C11 are not affected by this change in C1063. In fact, the definitions in C1063 apply only to C1063.
To return to the case in point, the contractor has bridged over a control joint using cold formed steel framing. The specifications stated that the steel framing cannot bridge over control joints. The contractor refuses to take corrective action because he does not believe that bridging the control joint will cause problems.
Control joints are used to prevent cracking of the overlaying materials and systems applied over the structure. While drywall is considered a flexible finish, it will crack when movement occurs in the underlying structure. The parameters for placement of control joints are specified in ASTM C840, Standard Specification for Application and Finishing of Gypsum Board: "A control joint shall be installed where a partition, wall or ceiling traverses a construction joint (expansion, seismic or building control element) in the base building structure.” I do not think this requirement could be any clearer.
The individual posing the question seems to think that MasterSpec or the American Iron and Steel Institute should cover these requirements in greater detail. The fact is that the new International Building Codes (I-Codes) reference ASTM standards and specifications for specifics of work to be performed. MasterSpec incorporates industry standards by reference just as the I-Codes do. AISI standards address the specifics of steel, both red iron and cold formed, structural and non-structural. AISI does not have an interest in the application of finish materials such as drywall.
There was also a request for technical backup to support the position of having the contractor install the control joints in the soffit. It seems to me that if the requirements are in the contract documents, and if it is a reasonable requirement, the contract documents should prevail. Remember that control joints play an important role ensuring that cracks do not appear in the finished surface. Done correctly, you will eliminate callbacks.
Don Smith is AWCI's director of technical services.