Water testing is complicated and as a contractor, if you have never had to be subjected to it, you can count yourself lucky. Water testing has made exterior plaster and EIFS work anything but business as usual. Most wall and ceiling contractors who work on condominiums have been around window water testing but may not really understand what is going on, what the rules are and how they should be applied. At the risk of being bold, many window experts and building envelope consultants don’t either, they just bluff very well. The following may help you when dealing with window troubles and water testing on walls. This is a very brief overview of a complicated issue.

Window Selection

All windows are not created equal. The performance grade per American Architectural Manufacturers Association standards determines how well a window will keep water out. (Tip: expensive looking windows do not always mean a higher performance grade or design pressure rating.)

To find the value of a window rating, you have to find the AAMA “gold” label. This label will be the only verification of the window’s performance value. Is the performance grade or design pressure correct for the project? This is not your concern but you might find it informative and helpful to see how the DP value correlates. (Tip: Too often, the DP or PG calculations are inadvertently incorrect.)

Design Pressure

There are two primary factors that architects should address when designing a building with regard to design pressures. First is the main wind force resisting systems, which include the structural components like wall framing, floor and roof diaphragms and shear walls. The second factor is the components and claddings, which deals with sheathings, exterior claddings, doors, windows and soffits.

There are four primary factors one needs to know to arrive at a DP for a specific building:

1.) Height of the building (average of the roof eave and the highest point of the roof).

2.) Importance factor of the building (Building Categories I-IV).

3.) Wind stagnation pressure of the building (three second wind gust from the code “Wind Speed Map”).

4.) Exposure (the determination of building’s exposure A-D).

The values are plugged into a calculation and a DP number is generated, then rounded up to the next increment of 5 psf. The selection of items 1 through 4 determine the DP is subjective, most notably the exposure factor. (Tip: Do not be afraid to question the values used to reach the testing DP rating. Do not simply accept them as the gospel from defect experts.)

The discontinuity factor is another item that comes into play. This typically refers to the parts of the building-usually corners-where pressures tend to be higher (sometimes twice as much as the field). Graphic 1 shows areas of discontinuity or high wall and roof zones. This is used to determine the DP for windows in those regions of the building. Determining the correct DP from the code is virtually impossible. The ASCE code standard is about 100 pages long. (Tip: Andersen Windows has a relatively easy-to-use DP estimator on its Web site. This online tool is only an estimate but pretty accurate and makes it much easier to verify the correct DP. Visit Google, type in “storm watch product finder,” then click on “design pressure estimator.”)

A mock-up getting ready for an E 331 test.


The water penetration test should follow ASTM E 1105 and AAMA 502-2 procedures. These tests should be conducted by an AAMA accredited lab. The AAMA lab is not allowed to have influence from outside sources and/or a conflict of interest. The lab typically tests fairly. (Tip: The lab will only test to the DP provided by the defect litigation firm or the specifier; so you might want to verify that the DP number is reasonably correct. Testing to higher pressure or longer periods of time is acceptable in limited circumstances.)

Once you determine the DP number is correct, testing starts. For structural tests, the base DP number is used at a 150 percent value. This is a pressure stress for how the windows withstand structural forces, not water penetration. For water resistance, the number is only 15 percent of the DP rating when tested at the lab.

For example, if it is a heavy commercial window with a DP rating of 40 psf, the water penetration test should be established at 6 psf for the laboratory. AAMA states that field testing should be at two-thirds of that value. The 6 psf is then multiplied by .667 and the test should be conducted at 4 psf, not 40 psf as stated on the window. There are a few exceptions to the above rules. First, the lowest DP figure for any window should be 2.64 psf. Second, AW-grade windows use a 20 percent value for the established DP.

A manometer is used to determine the water column pressure, which in turn can tell you what DP they are testing too.

The Water Column

You are now on site and a window water test is being conducted. You decide to see what DP they are testing the windows at. You note the test meter hooked up to the window reads 0.77 (see Photo 1). What does that 0.77 mean and how does that relate to the DP or PG of the window? The field testing agency verifies the DP by measuring the water column. A water column is created by the negative, which draws water up, much like using a straw to drink. The more pressure, the higher the water column rises. A window rated as HC 40 (see the PG chart) will be lab tested for water resistance at 15 percent of the 40 psf (or 6 psf). For the field test, the pressure is two-thirds (.667) of the 6 psf, which is 4 psf. Since the water resistance test requires knowing what the water column is and science tells that 1 psf of wind pressure drives water .1928-inches, a 4 psf will be a water column of .7712. Looking at the meter during the test tells us that the DP or PG for the window is an HC 40 psf.

A water test, per ASTM E 1105, using a design pressure.

ASTM E 2128

This is the standard for evaluating the water leakage of buildings. This standard is often misused in water testing as a tool by consultants using test pressures beyond what the established DP code requires. While the consultants are correct that E 2128 allows for increased pressure in terms of time and amounts of water, it is for the purpose of “recreating a known leakage problem.” This is fair if you own a building and the carpet gets wet every time a strong wind/rain storm occurs and you need to find out why so it can be fixed. It is not meant or intended to be used as a tool to create leaks to provide evidence in litigation support. It should be noted that item 10.2.7 states that “agreement” on testing methods and interpretation should between the interested parties “before” testing begins. If you are sent a notice that they plan to test per E 2128 and use a higher DP or longer period of time than stated, because E 2128 says they can, you need to find out the intent of the test. If the purpose is to find a “known” leak problem and then fix it, go for it. If they are doing the testing to build a court case against you, I think I would disagree in writing.

Water penetration testing is complicated and there are lots of rules, procedures and varying interpretations. If you are faced with water testing, hopefully this simplified overview can shed some light on the subject and encourage some good questions and guide everyone in the right direction. I would also suggest not fighting with the consultants. The contractor typically wants to solve a known leak problem too, and that it is done fairly and hopefully without burdensome and costly litigation.