General rules are difficult. Wall and window systems are devilishly hard to assess. Much of these systems are opaque, literally and figuratively. The most complex computer simulations fall short of reproducing the actions of air, moisture and heat in actual wall materials. It’s tough for any individual, or even a team, to master all the aspects of building science and practical know-how.
Still, there is a generally accepted methodology for a logical, comprehensive and cost-effective evaluation of exterior wall systems. Studies typically will include most of these steps:
1. Review of available documents
2. Personnel interviews
3. Visual survey of facade
4. Creation of inspection openings
5. Instrument recordings
7. Computer modeling
What does this look like in practice? I was part of a team investigating a building, constructed in the late 1970s, that houses community college classrooms and sports a steel curtainwall system (see Image 1). In this case, the failure is readily apparent as water permeates the walls in Image 2.
The owner assembled a team, including an architect, enclosure commissioning agent, and testing consultant to determine what and how much of the curtainwall to replace. The first step after the kickoff was to review all available documentation about the history of the wall, including design drawings and specs, shop drawings, previous studies, and maintenance and repair records. Then we interviewed knowledgeable staff.
The original design drawings were available and well crafted, clearly showing the insulated glass secured to the steel mullions with a rubber zipper gasket. (See Images 3a-b.) A careful field survey followed confirming, building-wide, that what could be seen matched the details. Still, the team wanted to confirm the interior wall structure and witness the deficits of the system in action if possible. This was a case for an inspection opening. Keep an open mind when your consultant says, “It is time to open a wall and force it to reveal its truth.” A small investment, and some inconvenience at this stage, can save much larger costs in testing later.
Making the Invisible Visible
A classroom was taken out of use and an area of the interior masonry bulkhead removed to reveal the back side of the spandrel panel below the window (Image 4). A fan was mounted in the classroom door to lower the pressure in the room and simulate a 20-mph wind against the facade (Image 5). Water was then applied to the exterior using a handheld spray nozzle (per AAMA 501.2, “Quality Assurance and Diagnostic Water Leakage Field Check of Installed Storefronts, Curtain Walls, and Sloped Glazing Systems) or a spray rack (ASTM E 1105, “Standard Test Method for Field Determination of Water Penetration of Installed Exterior Windows, Skylights, Doors, and Curtain Walls, by Uniform or Cyclic Static Air Pressure Difference”). Although water movement through walls is unpredictable, the leaks were apparent here. As an alternate to water, or to gain more information, theatrical smoke can be used to make airflow visible. In this case, both were used and each made dramatically clear that the zipper seal between the glass and the steel mullions had failed.
It was decided that a new glass retention system would be designed and retrofitted and, with all the glass replaced with argon-filled insulating units, the rest of the steel system could be refurbished.
A systematic process was followed that involved specific costly testing. You should know that it is rarely possible for consultants to determine, before beginning the investigation, what tests are going to be useful. When writing RFPs and budgeting, consider requesting unit prices for tests that seem likely to be needed and ask consultants to estimate the total cost for testing.