I’m working on a technical paper about design verification testing. That’s the radical new concept of testing wall and window assembly mock-ups to failure for air and water penetration so that you can see exactly what their limits are.
Currently, when window and wall-assembly testing is done at all, it’s done to some arbitrary standard to which everyone hopes the mock-up passes. But then you don’t know where failure lurks.
That’s something that anyone who constructs or owns a building needs to know.
As part of my research I spoke with Tom Schneider. the Director of Product Development for Building Envelope Innovations, LLC. During his three decades in the paint, coatings and sealant industry, Tom has developed architectural and high-tech ceramic coatings; and structural waterproofing and air management applications for the construction industry. A product-testing expert, Tom likes to say “if we are not testing, we are guessing. Guessing is very expensive.”
Here’s the gist of what he told me.
Buildings often fail due to water and air intrusion. Weather happens.
Those failures often engender enormous litigation and repair costs.
Energy is wasted when water and air infiltrate wall and window assemblies. The North American Insulation Manufacturers Association (NAIMA) claims that up to 35 percent of heat loss in homes can be attributed to air infiltration, in their white paper The Facts About Insulation and Air Infiltration.
When the water vapor carried in that warm air condenses on cold surfaces within the wall assembly, it can wet out insulation and other components. Wet insulation has little thermal resistance.
Wet walls can contribute to Sick Building Syndrome.
Sick building syndrome costs hundreds of millions of dollars annually, including the costs of increased respiratory illness and allergy rates from mold and mildew growing in wet walls.
Testing mock-up assemblies to find and fix leaks before construction — the proverbial “ounce of prevention” — is cheaper than repairing walls and windows when they do leak after the building is up. Yet testing is too often “not in the budget.”
If we are not testing, we are guessing. How willing are you to stake the well-being of a 20-story inhabited highrise on a guess? Incredibly, many construction professionals are willing to do just that.
If you don’t test your design with a mock-up wall assembly to the conditions the building is expected to face — a mock-up built with the same materials and procedures, by the same people who will do the building — Mother Nature will perform her own test.
And if she finds the flaw in the assembly — a flaw you could’ve found and fixed with a test — you could be liable for millions in repair costs. That’s the proverbial “pound of cure.”
Unfortunately, when there IS on-site mock-up testing, it’s typically inadequate.
That’s because the parties involved have a vested interest in the mock-up passing test. The contractor and owner both want the mock-up to pass, because if it doesn’t, that means delay and expense.
Sometimes, to ensure passing, they build the mock-up to a higher standard than will be used for the building. Sometimes, they test to easier conditions than the building will actually face. Sometimes they do both.
Sometimes they build the mock-up and don’t test it at all.
Tom recalled a multi-family condo in Northeast Portland (Oregon). The builders did a mock-up, then did everything possible to ensure it passed all the tests.
They used a window specially built just to pass the test.
Once the building was up, they confidence-tested the windows. The building had 300 windows. They tested random windows on each floor for air and water resistance. If the windows passed — like the mock-up — the test would end after 10 windows.
If a window failed, two more windows woud be tested, to restore confidence.
With 10 good windows, everyone could be confident most of the windows were good.
The only problem was that the window assemblies on the condo were not built to the special guaranteed-to-pass standards of the mock up.
The first window failed.
The second window failed.
Every window they tested failed. And they all failed in exactly the same place.
If the builders had tested a mock-up constructed with the same products and procedures used for the condo, they could have uncovered and corrected the problem immediately.
Instead, they bore the cost of replacing every window in the condo.
Testing should be to failure, not to artificially low standards. Design specification should consider actual geographic placement of the structure. Weather and surrounding structures have impact on what conditions the building will experience.
Typical ASTM tests are not adequate to predict the performance of the materials, assemblies or systems. Test committees do not often have construction experience.
Most testing is done under conditions the structure may never experience — 70 degrees Fahrenheit, 50 percent relative humidity.
You might think if you use the highest-quality proprietary materials backed by warranties, and install them strictly according to manufacturers’ instructions, those materials will all work as promised, and there will be no need to test.
You’d be wrong.
Product data-sheets will not indicate how the materials will perform in the presence of other materials.
Only preconstruction design verification testing will do that.
Testing doesn’t just save money by being more economical than repair. Constructing a mock-up under the same conditions, with the same people, products and procedures as will be used for the building confirms construction schedules and sequences. It helps determine labor costs, helps avoid pitfalls and educates everyone involved.
Meaningful design verification testing raises the level of expectation in performance of materials, assemblies and systems. When you know exactly, based on testing to failure, how far your materials can go, then you know exactly what you can expect from those materials.
That knowledge opens up opportunities for creative design, and results in energy-efficient buildings, better application methods, more cost-effective practices and healthier structures.
Anything less is a gamble at best.
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