The truth is no designer or contractor wants a leaky wall assembly. Past water intrusion problems into walls have created billions of dollars in damage, struck fear in the hearts of architects and led to some drastic overreaction and insane alterations. One such insanity is the overzealous and misuse of mock-up testing on exteriors walls for water intrusion. Codes were changed to meet the crisis but the International Code, in an attempt to address the past concerns of water instruction, has inadvertently created some confusion among designers, consultants, contractors and building owners. Some people seem to believe that all walls require water testing and the code proves it. They are mistaken. The rules in the code actually make sense when you interpret them correctly.

The Code

In Section 1403, Chapter 14 is entitled Exterior Walls and has the requirements for weather performance. This section establishes basic design and construction ground rules for design and construction of exterior walls. Section 1403.2 requires exterior walls to be weather-resistant. The envelope shall include flashing, per section 1405.3, and allow for drainage of water with a water-resistive barrier per section 1404.2. For us in the plastering industry, generic three-coat cement plaster over building paper and drainage EIFS comply with 1403.2 by incorporating both sections 1404.2 and 1403.2, and as such, do not require on-site water testing.

Exterior walls that are designed and constructed without flashings and/or a water-resistive barrier behind the cladding would require testing to verify code performance compliance. For example, barrier EIFS over framed walls would require water testing per ASTM E 331. The design pressure differential is established at a minimum 6.24 psf. This is fairly tough to pass and insures the wall will pass some pretty tough wind-driven rains. Fortunately, every EIFS manufacturer can produce a report verifying compliance with this test for barrier EIFS. Some consultants sell water testing for all framed walls as a good idea for added insurance. The problem is the use of these “non-required” water tests are not being administered correctly and then can lead to fixes just to pass a test, which can lead to unforeseen consequences or create future problems.

Mock-Up Testing

The designers and or consultants who sell water testing on mock-ups will often use design pressures that are not related to the buildings per the components and claddings section of the code. They will simply start ramping up pressure until they suck water through the exterior veneer through penetrations that have never been a problem. There is a code procedure to determine the proper design pressure.

If mock-up water testing is done on a wall, the test should be done with the insulation in the wall cavity and the gypsum wallboard installed and taped on the inside. This will replicate a real life scenario test. The interior finish should only be removed after the test to verify if an uncontrolled water leak has occurred. While ASTM E 1105 states the interior finish should be removed to view for leaks, this is intended for windows and doors only and meant to view window leaks and leaks between the window frame and adjacent exterior sidings. Removal of interior finish for window testing is appropriate as the in-place gypsum wallboard (interior finish) will have little to no effect on the window and its flashings during normal service life. However, exterior claddings will be greatly affected by the presence or absence of interior finishes. Testing exterior wall assemblies with the veneer cladding missing or the interior finish missing is testing an incomplete assembly. The information garnered from this test is pointless, false and misleading. It would be similar to testing a cars ability to stop, but removing the brake pads just prior to the test.

When these mock-up tests start sucking water through fastener penetrations, which virtually never happens in real life, workers are directed to put sealant around fastener penetrations to seal every tiny hole. This is not code required or recommended by the plaster industry. What about the long term detrimental affects the sealant may cause against the asphaltic building paper, felt or synthetic house wrap? One example of a latent defect is the sealant can leech the bitumens out of the building paper possibly resulting in premature failure of the water-resistant barrier. If you see brown staining around the edge of the white sealant, you have to ask what long term effect will this have on the paper. Contractors would be wise to warn designers in writing “this practice may have long term detrimental effects and we will proceed only as directed by you.”

Experimental ideas are just that, experimental and they carry liability. We know that fasteners have been penetrating asphaltic building paper for decades on tens of thousands of buildings in all types of weather with no issue, unless you put the wall cladding under direct negative pressure and to force water through to force a leak. We have lots of real constructability issues to solve, we do not need to fabricate or create additional ones.