Condensation Watch

AAMA 501.9 calls for curtain wall condensation testing before installation
Jason Seals
May 23, 2019
COMMERCIAL, RETAIL, FABRICATION : CODES & STANDARDS

The Bottom Line

AAMA 501.9 is a new test method from the American Architectural Manufacturers Association for verifying the performance of the design and installation of curtain wall systems. Keep watch for references to AAMA 501.9 in specifications for preconstruction wall mockups.  

Given possible liability consequences, manufacturers and contractors are well advised to verify the performance of the design and the installation method of fenestration systems before problems surface that will be time-consuming and expensive to rectify. To accomplish this, tests are available to be conducted on preconstruction mock-ups of representative sections in the laboratory.

For example, large curtain wall mock-ups are often built to replicate an area of fenestration and the surrounding wall construction that is representative of the actual building. Such mock-ups can then be subjected to a battery of tests. AAMA has developed several optional tests for curtain walls in its AAMA 501.n series, covering performance factors such as resistance to water penetration, seismic and wind-induced inter-story drift, seismic drift causing glass fallout, thermal movement effects of vertical inter-story movements, and even resistance to human impact.

Currently, AAMA 501.9, Surface Temperature Assessment for Condensation Evaluation of Exterior Wall Systems, is being finalized to join this family of test methods. It will prescribe a standardized means to evaluate the potential for the formation of condensation on interior surfaces under wintertime temperature and humidity conditions on large, job-specific curtain wall mock-ups. This is accomplished by measuring interior surface temperatures and comparing them to anticipated dew point temperatures likely to be experienced at the actual project site. 

Under the proposed assessment procedure, a representative section of the mock-up of the specific curtain wall system must be selected, measuring no larger than 15 feet (4.6 meters) square. If all the unique conditions cannot be represented in a 15-foot square section of the mock-up, it is allowable to require multiple assemblies as required to evaluate all the critical details. All parts of the specimen must be full size, using the same materials, details and methods of construction and anchorage as specified for the actual project. Portions of the interior wall representative of project conditions (e.g. drywall, insulation, etc.) should be included a minimum of 12 feet from the edges of the specimen to properly evaluate the perimeter conditions. Each operable element of the specimen must be securely closed and locked prior to testing.

To apply 501.9, the project specifier must determine the exterior and interior winter design conditions for the project, including interior temperature and humidity levels and exterior temperature. If no conditions are specified, default conditions are defined in the test method.

The test consists of sealing the mock-up specimen into the opening of an insulated laboratory test chamber. The outdoor side of the chamber is equipped with a means to lower the ambient temperature to the specified exterior winter design temperature. It also simulates air movement using wind generators to provide an air flow of 12.3 ± 3 miles per hour (5.5 ± 1.3 meters per second). The indoor side is equipped with a means to both control temperature and limit relative humidity to prevent the formation of condensation in the areas where surface temperature data is recorded. Indoor air circulation is established so as not to exceed 1 mile per hour as measured near the bottom and top of the mock-up. The interior ambient air temperature near the test specimen is instrumented with three thermocouples located near the top, middle and bottom of the test area. 

Test duration is a minimum of two hours after all recorded interior surface temperatures have achieved steady state conditions. The time will vary with the material composition of the wall, e.g., masonry vs. metal components. All surface temperature data is compared to the specified dew point for the project and all locations at which temperatures fall below the dew point are identified.

Note that this test method is for determining cold spots for the purposes of predicting the occurrence of condensation at the project’s specified winter design conditions. It does not provide a Condensation Resistance Factor, or CRF, rating such as that generated by AAMA 1503.

When published, AAMA 501.9 will be yet another test architects and consultants can specify for preconstruction wall mock-ups. Since large curtain wall mock-ups require a lot of planning, coordination and expense to build, it is often advantageous to add some of the other optional tests as well. After all, in the final analysis, testing is a lot less expensive than revisions after the fact. 

Jason Seals is certification manager for the American Architectural Manufacturers Association. He can be reached at jseals@aamanet.org.