Implications of Allowing Substitutions in an MCM Wall Assembly

An MCM wall assembly is a complex assembly that quite often includes inter-related structural, water, air and insulation components, in addition to the exterior cladding itself. Designed to meet various codes such as NFPA 285, Section 1407 of the IBC, and ASHRAE 90.1, the wall assembly must be tested as a complete and integrated system. Once a system has passed the stringent testing requirements, this indicates that all of the products are working together to achieve a specific performance requirement. If any component of the tested system is changed, it is likely to impact the performance of the wall assembly as a whole.

Design professionals spend significant time to research and design a building that meets or exceeds code requirements, as well as remains aesthetically pleasing and within the owner’s budget. What should you do when the Division 7 specification is carefully developed and finalized, but another party wants to request a change to the assembly?

Here are some considerations and potential implications of accepting substitutions:

• Lack of required performance – Different products, or different product configurations, may result in insufficient performance in the wall assembly and not meet the requirements of the project. While the system may not entirely fail, a product substitution may reduce the system performance, and not meet one of the performance requirements.
• Product or system failure – If one of the components in the MCM assembly is changed, it is possible the substituted product or the entire wall system could fail.
• Warranty is voided – Because a manufacturer-designed system is a pre-engineered and fully tested MCM system, the manufacturer’s warranty may become null and void since the exact components were not installed in the assembly as tested.
• Noncompliance with building codes – Again, because the MCM wall assembly is tested as an entire system, to meet the various building codes, the system must be installed as it was tested. While the system may perform satisfactorily, it may not be code compliant.
• Impact on other components during installation – Substituting one product within the wall assembly could require changes to the accessory products required for the installation or could require changes to various details on the project to allow the products to function together properly. This is especially true when substituting insulation systems within MCM wall assemblies. Each insulation system works differently and requires project-specific detailing that will vary from the originally specified system.

Now that we have established the potential risks associated with substituting a wall assembly component, how do you decide to accept or reject a proposed substitution? Is it enough to approve a substitution based on a completed substitution request form? Have you received a detailed product comparison showing the differences between the specified product and the proposed substitution, as well as a cost analysis including both material and labor costs? Unfortunately, more often than not, this means additional time and research to evaluate the substitution request.

This is where a professional engineer (PE) and engineering judgements can assist you. An engineering judgement provides an assessment of component substitutions that vary from the tested wall assembly design configuration. It is validation that a substituted component has performed similarly to the tested component and should still meet the overall performance requirements when incorporated into the assembly. In some cases, it is not enough to have an engineering judgement or text extension letter provided from a manufacturer; it must be reviewed and stamped by a licensed PE prior to being submitted to the local building official for acceptance. It is important to note that engineering judgements are project specific and oftentimes the PE must be licensed in the state in which the project is located.

All things considered, even if a substitution is approved by a PE, it is important to review the original specification and manufacturers’ warranties to determine potential future implications. Do the risks of saving time or money today outweigh the long-term benefit of proceeding with a manufacturer-designed, pre-engineered, MCM wall assembly that has been fully tested and proven to perform?

Shawn Crouthamel, is the national sales manager at Laminators Inc. in Hatfield, Pa. For more information, visit www.laminatorsinc.com.