Proving Ground: Performance Mock-Ups as Proof of Concept and Constructability Tools

Proving Ground: Performance
Mock-Ups as Proof of Concept
and Constructability Tools
Ryan Upp, AIA
Simpson Gumpertz & Heger | Los Angeles, CA
rnupp@sgh.com
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ABSTRACT
Design solutions must be buildable in the real world. Facade design intent, geometry, and materials must come
together in a way that allows structural loading, environmental protection, and optimal long-term performance.
Performance mock-ups bridge the gap between conceptual design and construction and allow project teams to test
expectations and fine-tune plans prior to installation. This step is particularly important when working with innovative
facade designs that incorporate new materials or complex integrations between various standard assemblies.
A performance mock-up is commonly understood as a tool to test previously untested cladding and glazing assemblies.
However, it can also be a valuable tool for understanding constructability, sequencing, and integration detailing.
Transition detailing, in particular, is unique to each project. Although the design may include transition concepts and
shop drawings may be carefully detailed, getting the systems to work together can be a challenge and result in unintended
design changes, as well as schedule and cost impacts during construction.
In this paper, I will explore how performance mock-ups translate design intricacies into constructable assemblies,
and ultimately, a successful project. I will discuss laboratory and on-site mock-ups and how to make the most of each,
including strategies for planning, timing, testing, and follow-through.
Ryan Upp, AIA
Simpson Gumpertz & Heger | Los Angeles, CA
Ryan Upp, AIA, is a senior project manager in the Building Technology Division of
Simpson Gumpertz & Heger’s Los Angeles office. He is an architect registered by the State
of California and has experience on a wide range of historic and contemporary structures,
consulting with architects, contractors, and building developers. His experience includes
investigation of existing building enclosures, restoration and remediation repair design,
and new-design consultation encompassing a variety of systems, including below-grade
waterproofing, plaza deck waterproofing, balcony waterproofing, exterior wall and cladding
assemblies, curtainwall and window assemblies, and roofing.
SPEAKER
Design solutions must be buildable. Facade design intent, geometry, and materials must come together in a way that allows structural loading, environmental protection, and optimal long-term performance. Performance mock-ups (PMUs) bridge the gap between conceptual design and construction and allow project teams to test expectations and fine-tune the design prior to installation. This step is particularly important with innovative facade designs that incorporate new materials or complex integrations between assemblies, as well as with simple designs and traditional assemblies.
A PMU is a tool to test performance of cladding and glazing assemblies. It is also a valuable tool for understanding constructability, sequencing, and transition detailing. Transition detailing is unique to each project, and while the design may include transition concepts and shop drawings may be carefully detailed, getting the systems to work together can be a challenge and can result in unintended design changes, as well as schedule and cost impacts, during construction.
This article discusses types of PMUs and how to make the most of each type; strategies for planning, timing, testing, and follow-through; how to avoid pitfalls in design, construction, and testing; and ultimately how PMUs translate design intricacies into constructible assemblies for a successful project.
MOCK-UP DESIGN, CONSTRUCTION, TESTING, AND EVALUATION
Mock-up Types
A mock-up is defined as a “full-size model built to scale for study, testing, or display.”1 Construction mock-ups vary in scope and complexity depending on what they are intended to accomplish. Common types of mock-ups include visual, component, system, and performance. A visual mock-up allows for aesthetic review of components, colors, finishes, and workmanship (Fig. 1). Component mock-ups are small scale and can be used to study pieces of a larger assembly, such as a complex sheet metal shape or unique mullion profile (Fig. 2). A system installation mock-up, such as a window installation or initial waterproofing application, helps confirm preparation and installation prior to full production, and allows initial quality assurance testing (Fig. 3). While these types of mock-ups are useful, they are limited. A PMU combines the visual, component, and system mock-ups into a single installation and allows testing of various performance metrics, as well as a more comprehensive evaluation of construction detailing, sequencing, and discovery of unanticipated conditions (Fig. 4).
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Proving Ground: Performance
Mock-Ups as Proof of Concept
and Constructability Tools
Figure 1. Visual mock-up.
Figure 2. Component mock-up.
Figure 3. System installation mock-up.
Figure 4. Performance mock-up.
PMU Considerations
A PMU can be built, evaluated, and tested in a laboratory (Fig. 5), on site or near the project (Fig. 6), or in situ within the building construction (Fig. 7). Project conditions (complexity, schedule, budget, and available space) generally dictate which location is most appropriate. Evaluate each alternative for intent, scheduling, and cost-effectiveness. Assess design complexity, previous performance history, and combinations of products and materials. Appraise the need or desire to validate performance expectations through testing and the potential need for rework or retesting of all or part of the assembly if the PMU does not initially perform as intended.
The type and extent of testing desired drives decisions about the PMU type and location. A laboratory setting allows the most extensive testing because it has prebuilt testing chambers, available testing equipment, and designated space. Some tests, such as the effects of simulated building movement, can only be performed in a laboratory setting. Most other tests, such as air and water infiltration tests, can be performed with on-site mock-ups. In situ testing is generally the most limited option, due to building constraints. Laboratory and on-site testing can be completed before or at early stages of construction so that the results can be used to inform the design or construction process prior to full implementation on the building. The results of in situ testing, which occurs during construction, necessarily limits the type and extent of modifications that can be made because materials have been ordered and work is ongoing.
Consider the convenience of available PMU construction and testing spaces. A nearby laboratory testing facility will be reasonably easy for the design and construction teams to access, and it allows PMU construction to be performed by the builders who will be performing the final work. A testing facility that is farther away limits access and makes coordination more difficult—builders performing the final work may not be able to work on the PMU or they may require special accommodations to do so, which affects cost and scheduling. An on-site PMU requires open space, such as plaza, landscape, or parking areas. A constricted and busy site may not accommodate an on-site PMU. There may be nearby space available in parking lots or other open spaces, but permission or leasing arrangements may be required to use them. An in situ PMU requires no special facilities or space and can potentially become a part of the finished work; however, fabrication schedules and construction sequencing may restrict the extent of the mock-up and limit one’s ability to conduct desired testing (for example, it may not be possible to perform water testing an in situ mock-up over work in progress below).
Consider the project schedule. A PMU should be constructed and tested prior to construction of the relevant components. Laboratory testing facilities have a finite amount of space, which may be reserved already. If laboratories are unavailable, testers must rely on on-site or in situ PMUs. A particularly aggressive project schedule may not allow for laboratory or on-site mock-up construction and evaluation, whereupon an in situ mockup may be the only viable option.
Consider the project costs. PMU construction, testing, and evaluation should be included in early construction cost estimates to allow evaluation by the owner, design, and construction teams to avoid unexpected costs. A laboratory PMU is typically the most expensive, followed by on-site and in situ. Costs will be impacted by the complexity and extent of the PMU, intended testing and evaluation, and the need or desire to rebuild or retest.
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Figure 6. On-site performance mock-up.
Figure 5. Laboratory performance mock-up.
Figure 7. In situ performance mock-up.
PMU Design
Design the PMU to represent project-specific conditions. Evaluation reports of components or assemblies by manufacturers or fabricators are useful to understand expected performance, but they typically do not evaluate adjacent assemblies, transitions, or concealed conditions. As the finished building is ultimately intended to perform holistically, it is important to confirm that the various components will function adequately together.
Include typical elements of the exterior wall system in the PMU, and evaluate whether mock-up of nontypical conditions provides value to the project. Mock-ups vary in size and should be coordinated with specific testing requirements. Consider how much space for the PMU can be accommodated by the laboratory or on site. In some cases, multiple PMUs may be necessary to consider all relevant conditions. Generally, the PMU should include the following (Fig. 8):
• One or more typical vertical and horizontal bays, enough to represent repetitive components
• Typical vertical and horizontal conditions and transitions
• Inside and outside corners, if appropriate
Mock-up of project-specific concealed conditions is particularly important, as a failure on the building will be difficult and costly to remediate. Inclusion of unspecified components or detailing, in lieu of project-specific components or detailing, will not give the project team the same level of confidence in the constructability or performance. For example, at cladding panels, if unspecified concealed clips are used for convenience to expedite cladding installation, the specified clips cannot be evaluated for installation and weather barrier continuity.
For laboratory or on-site mock-ups, while the PMU should be project specific, multiple representative sample conditions can be included in a single PMU. However, it is important to understand that the edges of the PMU are likely a non-project-specific condition; thus, details and components that are intended to be tested should not be located too close to the edge. The design and construction teams must consider not only which assemblies and transitions will provide the most benefit to mock-up but also how to transition them, including non-building conditions. Although not part of the building design, these transitions will essentially be required to pass PMU testing; however, they generally cannot be isolated, and testing failures can be difficult to attribute to a non-building condition only.
PMU Construction
To the extent practical, construct the PMU to mimic building construction. Account for logistics, sequencing, crating, staging, and other factors that mimic building field conditions. This process may reveal special requirements that might otherwise cause delays or increase costs. Ideally, the same forepersons and crews in the trades responsible for the work on the building will construct the PMU (Fig. 9). This allows the builders to practice and help identify and resolve unforeseen
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Figure 9. Performance mock-up in construction.
Figure 8. Performance mock-up extent.
conditions, special sequencing, or special techniques
required, which in turn reduces the risk
of delays and improves quality assurance during
construction.
While the PMU should represent building
construction, there will be challenges
to simulate project-specific conditions on
a steel testing chamber at a laboratory or a
stand-alone wall assembly on site. Consider
how the mock-up is
attached at the edges to
the chamber, supported
on site, and transitioned
to grade. These conditions
may be unique to
the PMU, but it can be
difficult to accurately
diagnose a testing failure
near the PMU edges. For
example, exposed slab
edges must be recreated
without the full slab in
the chamber but also
designed to allow simulated drift testing.
As part of the construction process, consider
in-progress observations of the PMU by
the design team and product manufacturers
for quality assurance, as might be performed
on the building. Before installed materials are
covered by subsequent materials, review the
installed materials and workmanship for compliance
with the design documents and manufacturers’
requirements.
Similarly, consider performing
quality assurance
testing, such as
material bond strength
testing or thickness
measurements. Quality
assurance evaluations
during PMU construction
will help eliminate
construction deficiencies
that could lead to
PMU testing failure.
Consider “pretesting”
partially installed
assemblies to identify
areas that require remediation, redesign, or
reinstallation that might otherwise contribute
to PMU testing failure after these components
are concealed. For example, it may be advisable
to perform water testing on a wall assembly
that includes weather barrier and penetration
detailingbefore covering by finish cladding;
the test results may provide early indications
of whether installation is successful, while it is
still relatively easy to make repairs or changes.
Performance Testing
Performance testing checks the wall
assembly’s ability to meet design performance
expectations. Evaluate and select testing in the
context of previously tested or untested assemblies,
the transitions between assemblies, anticipated
environmental conditions, performance
expectations, and level of acceptable performance
risk. When selecting performance tests,
consider other factors noted previously, including
available laboratories and space, schedule,
and cost.
Evaluate test methods and required test
values for project-specific conditions. Consider
whether the proposed tests are valid for project
conditions, and if the values are appropriate
for the project requirements. Require test loads
for the PMU based on local conditions and
building code and jurisdictional requirements.
Coordinate the required test values with the
specified products and assemblies. The tests
and values can be more (or less) stringent than
standards published by ASTM International,
American Architectural Manufacturers
Association, or other industry organizations,
provided they comply with regulations and
meet the owner’s performance requirements.
Laboratory PMU testing is guided by
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Quality assurance evaluations
during PMU construction will
help eliminate construction
deficiencies that could lead to
PMU testing failure.
Figure 10. Laboratory testing.
Figure 11. On-site testing.
ASTM E2099, Standard Practice for the Specification of Pre-Construction Laboratory Mock-ups of Exterior Wall Systems,2 which covers testing for air and water infiltration before and after the application of building design loads, effects of wind pressure, and vertical and horizontal movement between stories (Fig. 10). At the project team’s discretion, more (or less) testing can be performed. Air and water infiltration and structural testing are generally required, but optional tests include thermal performance, condensation risk, acoustic performance, and window washer anchorage.
On-site and in situ PMU testing are not currently guided by a singular industry standard. As noted previously, some, but not all, of the testing that can be done on a laboratory PMU can also be done to on site or in situ PMUs (Fig. 11).
Failures, Rebuilding, Retesting, and Deconstruction
Evaluate testing failures to determine when portions (or all) of the PMU should be reconstructed to implement revisions based on initial construction and testing results, and when the revised PMU should be retested. ASTM E2099 generally does not require retesting upon failure (although there are certain exceptions), so it is incumbent on the design team to specify the intent and requirements for retesting after failures.
To obtain the greatest value from a PMU, evaluate failure modes, make repairs, and retest to confirm the efficacy of the design or construction methodology; acceptance of testing failure does not generate proof of concept. “Band-Aid” repairs to make a mock-up artificially pass testing should be used with caution; they are only allowable if they do not influence the performance of adjacent components, if the cause of failure is known with certainty, and if the remediation for the building is proven. For example, adding sealant to prevent water entry into the glazing pocket of a PMU curtain wall assembly that is not intended to be installed during fabrication, can result in a false pass, which may fail on the building. In general, make PMU repairs to comply with the design intent of the construction documents, as modified by lessons learned from the original PMU, or redesign and rebuild the failed component to meet expected performance criteria (Fig. 12–14).
While it is easy to suggest repeated repairs and retesting, there is a cost and schedule implication to doing so. If initial testing fails and subsequent testing continues to fail after repairs are made, it may be tempting at some point to accept the test failures and move on to building construction. Before moving on, it may be prudent to reconstruct sections of the PMU
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Figure 12. Failed original joint installation.
Figure 14. Successfully reinstalled joint installation.
Figure 13. “Re-engineered” joint.
rather than trying to continue to make repairs. As a last resort, failures could be accepted. This decision should be made carefully on a case-by-case basis; conditions should be evaluated by the design, construction, and ownership teams to understand the most likely failure modes and if they can realistically be resolved in situ, as well as to understand the potential performance risk. In such cases, it is advisable to conduct follow-up in situ testing to confirm performance.
Documented deconstruction of a PMU is advisable in some circumstances. Suspected failure at concealed conditions or of an isolated component may require further analysis to develop an effective, repeatable remediation, which may require partial deconstruction to understand a flaw in the design, fabrication, or installation (Fig. 15). Similarly, if test failure is accepted as noted previously, observations of the suspected failure mode may provide some confidence in the proposed repair without additional testing.
COORDINATION AND
SCHEDULING TOOLS TO REDUCE UNFORESEEN CONDITIONS
Unforeseen Conditions
and Common Pitfalls in Design, Construction, and Testing
As discussed previously, a PMU can be used to flush out unforeseen issues in design, fabrication, or installation prior to full implementation on a building. When using a PMU, thorough coordination, scheduling, observation, and communication will reduce such issue, improving the likelihood of testing success and minimizing costs, if any, for follow-up reconstruction and retesting.
Common pitfalls in design include inadequate consideration of transition areas. This is particularly true of areas that combine complicated geometries, movement requirements (seismic, expansion, drift), or both with multiple materials and components, which may be installed by different trades. Communicating design intent in two-dimensional plan and section drawings is often not adequate to fully develop transitional design. Isometric or sequence detailing is necessary to understand complex transitions.
Common pitfalls in construction include the incorporation of unspecified materials and components and non-project-specific conditions. Unspecified materials and components are sometimes used in concealed conditions for convenience or to expedite installation or testing. Detailing around these unspecified components allows a testing failure or pass that is not fully applicable to the building. As noted earlier, a PMU may include non-project-specific conditions, such as perimeter/support conditions that are unique, to allow construction and testing of multiple assemblies on a single PMU. These conditions are typically not detailed in the design documents, but they are nonetheless required to pass testing if they cannot be isolated. In addition, many PMU test failures are not due to design flaws; rather, they are caused by incorrectly installed components, which must be removed and reinstalled for additional testing.
Common pitfalls in testing include insufficient coordination and equipment failure. “Wet” components, such as sealant, must fully cure before testing. Pretesting, or even full testing, is occasionally performed on uncured components, resulting in failure and the need to reinstall, cure, and retest. If PMUs are subjected to rain or water from adjacent testing or cleaning and not fully dried before testing, it is difficult to accurately assess the source of water leaks. Misplaced testing gauges do not provide accurate measurements, resulting in misdiagnosis. Furthermore, misplaced gauges can cause damage to PMU components, such as glazing, that might require replacement before retesting. Finally, if test equipment such as a propeller or water spray rack fails to operate properly on the day of the test, a retest may need to be scheduled.
Coordination Tools
Coordination among the owner, design team, contractors and trade partners, and testing agency is necessary to get the most value from the PMU process and to minimize PMU costs and schedule delays. The PMU purpose execution, evaluation, and expectation must be commonly understood by the project team. Although the design team is generally responsible for specifying PMUs, testing, values, and pass/fail criteria, the PMU effort should be collaborative. Define the roles of the project team early in the process: the owner defines the performance requirements (meets or exceeds jurisdictional requirements); the designer designs to meet the performance requirements and establishes the PMU parameters; contractors and trade partners provide feedback on constructability, performance expectations, and costs for the owner and designer to consider; and the testing agency provides final proof of concept by conducting specified testing.
Identify the type of PMU, conceptual PMU assemblies, extent, and testing early in the design phase. As PMUs and testing affect costs and schedules, the design team should identify the intended mock-ups and testing during the design phase, obtain owner buy-in, and include the mock-ups in construction cost estimates. This may require discussions of costs versus benefits and risks to define the PMU process.
Identify the assemblies to be included in the PMU in the construction drawings. As
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Figure 15. Deconstruction of performance mock-up components.
noted in ASTM E2099, the assemblies should be identified either by designating an area or areas on the architectural elevations or by providing separate mock-up elevation drawings that may combine various typical parts of the wall systems into a single mock-up. Evaluate the building geometry and various components to determine which is the most appropriate approach. In addition to elevations, provide wall sections and details, or references, as necessary. As discussed previously, a composite PMU may require transitions that are not included in the building; detail these areas to reduce risk of testing failure. Finally, identify critical points in the assembly, such as stack joints and transitions, where special viewing access may be needed.
The construction specifications indicate required testing, performance values, and more. Specifications include many individual sections that will be part of the PMU; however, specifications are not always fully coordinated. In addition, required testing described in any given section may be questioned as to its applicability to components of another section. As such, consider a stand-alone PMU specification section, or, alternatively, a comprehensive exterior cladding system specification, that references the various related sections and also provides a single place to define the PMU type, testing regimen, evaluation protocol, performance values, and other mock-up requirements, which can be noted as a catch-all to “govern” in the event of discrepancies among other specification sections. In addition, clarify if only specific components of the PMU are being evaluated or if all components including transitions, terminations, etc. will be evaluated.
Require material product data and shop drawing submittals for the PMU. The shop drawings should fully detail materials and components, transitions to adjacent assemblies, edge conditions, and viewing platforms. Consider requiring coordinated shop drawings that integrate various trades’ work into a single coordinated drawing set. Coordinate with the testing facility for the location of temporary supports and mounting locations for gauges. In addition, require submittal of test procedures and evaluation protocol for confirmation.
Conduct a PMU preconstruction meeting that includes all relevant parties to review approved shop drawings, testing procedures, and anticipated sequencing and schedule. Use the meeting as a tool to coordinate trades, understand cure times, and identify areas that may need further development or input by the design team.
Coordinate construction with the design team and manufacturers’ representatives to make periodic observations for compliance with design intent and manufacturers’ requirements. Make observations to document each “layer” of construction before it is covered by subsequent components. Have multiple parties review “final” construction and test setup before testing, with enough time to make minor repairs or adjustments.
Evaluate PMU construction as it is built to provide feedback on areas that work as intended or need further modification and evaluation. The contractor should maintain a record of as built mock-up construction, indicating in detail any changes or modifications to the PMU. Following successful testing, the design team should incorporate any changes to the design as a result of the PMU process into updated construction documents. Because PMU modifications may need to be interpolated to various assemblies on the building, relying only on as-built drawings or notes of the PMU to document design changes risks overlooking an important modification.
Scheduling Tools
The most important aspect of scheduling the PMU is that it be completed, tested, and approved before procurement and construction for the building (or relevant components), and with enough time to incorporate any design modifications. If the PMU process is completed after facade construction is underway or after cladding components are already in fabrication, it could be infeasible to incorporate modifications. For laboratory or on-site PMUs, coordinate the PMU schedule with the laboratory facility or on-site space requirements. In addition, consider accounting for time in the schedule to repair and retest the PMU; most PMUs will not pass the testing the first time for a variety of reasons. Remember, the PMU is intended to be a problem-solving tool, not a formality.
Understand the critical path to a successful test relative to component procurement and building construction. Establish a milestone schedule for the PMU, accounting for submittals and shop drawings, and in-progress reviews to observe components before they are covered. In addition, keep in mind that many concealed materials are not intended for long-term exposure to ultraviolet light and may degrade over time. Delays in cover, repairs, or testing can lead to testing failures from material degradation, potentially requiring additional repairs and testing.
HOW CONSTRUCTION PROCESS AND TESTING CALIBRATE FINAL DESIGN AND CONSTRUCTION
Construction Process
The purpose of a PMU is to provide proof of concept for the design performance intent and the construction means and methods. The PMU construction process can identify many potential design and construction issues on a small scale, allowing the opportunity for modifications prior to full implementation, which reduces the risk of schedule and cost increases on the building.
Previously untested assemblies or combinations of materials and components include some risk of performance failure, either due to design, fabrication, or installation. A PMU allows practice installation, which can in turn help to identify deficiencies and develop remediations to allow the design to perform as intended.
Design integration between materials or components may not be well developed in the construction drawings. Alternatively, design intent may be clear enough in two-dimensional plan and section drawings but underdeveloped across complex three-dimensional geometries. Even with building modeling software, small-scale transitions can be overlooked or misunderstood until visible, creating an unforeseen condition. A PMU allows discovery of underdeveloped transitions, as well as input from subcontractors on constructability at these transitions, so that solutions can be prepared and tested.
Along with transitional design details, complicated assemblies may require multiple attempts to build correctly. The PMU provides the opportunity to develop efficient means and methods for complicated transitions and best practices for specific conditions. The efficiencies learned on the PMU can be applied to the building. Any number of construction oversights may occur, such as noncompliance with design detailing, insufficient laps, or unrepaired damages. As these issues are identified on the PMU, special attention can be emphasized for these same areas on the actual building.
The need to install one product or component before another is not always clear in the design drawings. Alternatively, sequencing may be clear enough but may require one trade’s scope to be interrupted by another’s. A PMU helps clarify sequencing requirements, allowing for better planning and scheduling, or identifies areas that may be more efficiently constructed with alternative detailing.
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A PMU allows discovery of timing or scheduling impacts. Necessary modifications to components or alternative components could have lead times that impact the overall schedule. Early discovery of such issues can potentially mitigate delays or at least provide information to make informed decisions about delays versus performance.
Testing
Successful performance testing provides the final proof of concept for both design and construction. Successful testing proves the design, materials, and methods will work as intended. However, the process of achieving successful testing is how the design and construction are fine-tuned. Testing failures offer the design and construction teams the opportunity to evaluate the cause of failure and implement changes to achieve success. Multiple rounds of testing may be required to confirm that the changes work as intended.
To get the most value from the performance testing process, only “engineered” changes to the design or construction should be completed, and these changes should be done in the same manner that they would be implemented on the building. Retesting short-term or “nonengineered” repairs that are made only to expedite PMU testing success will not fine-tune the final design or construction and will leave some doubt as to proof of concept.
Documentation and Implementation
Because the PMU is a tool to evaluate design and construction prior to full implementation, it is critical that modifications to the design and lessons learned in the construction be incorporated in the project. If the mock-up is performed too late to make meaningful changes, or if there is no documentation of changes and plans for implementation, the PMU becomes a mere formality and may not add substantial value to the project.
ASTM E2099 generally requires as-built drawings of the PMU showing any changes to the design, as well as a final test report. However, simply meeting these requirements may not be enough to get the full value of the PMU process. Methodology and responsibilities should be established for documenting design changes and construction means and methods, and for how design changes will be implemented. In addition to as-built drawings, photographic documentation of the overall process and detail assemblies allows a virtual deconstruction and analysis of areas in the event of localized test failures. Written observations and analysis of pretesting, full testing, and retesting, or acceptance of failures, and any design, means, or methods modifications create a narrative for further evaluation and an additional basis for implementing changes on the building.
EVALUATING THE COSTS
AND BENEFITS OF PMUS
Table 1 summarizes pros and cons of laboratory, on-site, and in situ PMU types. This information can be useful when performing a high-level cost-benefit-risk analysis for the PMU types, including not providing a PMU at all. The potential results of a PMU do not always justify the expense; however, stakeholders may consider the cost of a PMU to be a relatively low-cost investment to reduce the risk of relatively high-cost performance failure, unforeseen conditions, and schedule and construction cost changes while in full production on the building.
Laboratory PMUs are generally of most value to projects with complicated geometries, transitions with multiple materials and components, previously untested assemblies or combinations of assemblies, and custom fabrications—particularly if capacity for differential movement is also required. In addition, laboratory testing may benefit projects with potentially high costs or substantial risks associated with failures, such as loss of use or litigation. A nearby laboratory maximizes the value of this PMU type by easy access for the design and construction teams. Although testing at a remote laboratory may be costlier, it can still be beneficial in some cases.
Compared to laboratory PMUs, on-site PMUs may provide a better value for projects with limited differential movement, comparatively simple geometries and transitions, limited components, and traditional combinations with a history of similar installation and good performance. Previous performance history might negate the need to test for movement and post-movement air and water infiltration, with relatively low risk. However, the on-site PMU will still allow for fine-tuning and adjustments for project-specific conditions. Lack of a nearby laboratory may increase the value of an on-site PMU, which could provide many of the same benefits as laboratory testing without excessive cost for travel or loss of interpretation between builders. An on-site PMU could also be considered a compromise to accommodate space, schedule, or cost constraints while still allowing more testing and evaluation prior to fabrication or construction than could be achieved with an in situ PMU.
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Type
Pros
Cons
Laboratory
• Allows testing not possible with other PMUs
• Allows modifications to design, fabrication, or
construction to be implemented (potentially)
• Most expensive
• Requires the most coordination
• Requires a laboratory testing facility, and team
members must travel to and from the facility
On-site
• Allows some of the testing that can be done in
laboratory
• Allows modifications to design, fabrication, or
construction to be implemented (potentially)
• Moderately expensive
• Requires moderate coordination
• Requires space to build and test
• No structural movement testing
• No air/water infiltration testing following
movement testing
In situ
• Least expensive
• Requires the least coordination
• The PMU may potentially remain as part of the
finished work
• May required multiple mock-ups to review all
areas of interest
• Only allows limited testing and observation
• Only allows minor modifications to design or
construction, more in line with quality assurance
Table 1. Pros and Cons of Performance Mock-ups (PMUs)
In situ PMUs are most appropriate for projects with simple geometries, materials and components with proven track records of performance, and simple and limited transitions. Although the in situ PMU provides performance validation for design and construction, it is more of a quality assurance test for installed components to confirm performance is the same as it was in the past. An in situ PMU may be appropriate in situations where there is little reason to anticipate performance failure and it is unlikely that design or construction changes will be necessary.
Omission of any type of PMU can increase risks for cost increases, schedule delays, performance failures, and undesirable aesthetic changes. In addition, omission of a PMU may limit the owner’s, design team’s, and builder’s confidence in the project success, which may, in turn, have insurance or future litigation implications.
SUMMARY
Facade designs range from simple to complex, but regardless of the level of complexity, they are expected to fulfill an aesthetic vision and provide a safe environment for users over the course of the building’s life cycle. PMUs allow testing of design solutions for constructability, sequencing, transition and integration detailing, and expected performance. Lessons learned as part of the mock-up construction and testing process can be incorporated into the final design and construction to reduce the risk of unintended design changes, schedule, and cost impacts during full implementation. Successful mock-up construction and testing provides a proof of concept for the design itself as well as the construction means and methods, and should provide the owner, design team, and contractor a high level of confidence in project success.
REFERENCES
1. Merriam-Webster.com Dictionary. “Mock-up.” Accessed May 5, 2021, https://www.merriam-webster.com/dictionary/mock-up
2. ASTM International. Standard Practice for the Specification of Pre-Construction Laboratory Mock-ups of Exterior Wall Systems. ASTM E2099-00(2014)e1, West Conshohocken, PA: ASTM International, 2014.
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