With proper design and clear specifications, it only remains to confirm that the window is installed properly in the field to make certain that the desired performance is achieved.
First, try to make sure that the windows on site are the ones that were specified. Check window labels (see Figure 4), invoices or shipment waybills for the model and manufacturer, and glazing options. Low-e coatings are impossible to verify just by looking at them, but there are ways to determine whether a window has a low-e coating (even if it is not possible to verify that it is the exact coating that was specified). A commercially available, handheld electronic device can be used to determine if a low-e coating exists and on which surface.
For a low-tech version of the same verification, use a flashlight, butane lighter or other source of light. With the light source held at the correct angle, a reflection of the light source from each surface will be visible. If there are no low-e coatings, the images will be similar, but if a low-e coating exists, the reflection of the light source off that surface will be different.
A low-e coating reduces the amount of energy transmitted in the long-wave part of the spectrum, so more of those wavelengths will be reflected back toward the viewed and the image will appear redder than the others. A black surface behind the window makes viewing easier.
Once the product has been verified as being what was intended, several field tests can verify the performance of the installed product. These include noise transmission, air leakage, ease of operation and water leakage.
Noise transmission
ASTM E966 is the field version of the STC lab test. A decibel meter and calibrated sound source are required. Several measurements are taken from the interior and the exterior, with the decibel reduction computed and converted to an STC rating as per the Standard. The specifications should indicate acceptable levels, recognizing that the fieldmeasured STC will not meet the same level of performance as the lab-rated specimen.
The tests should include the wall-window interface when performed in situ. This will not confirm the window rating, but will demonstrate the actual performance.
Air leakage
Portable air-leakage test units are commercially available. These units contain a vacuumcleaner motor and a calibrated airflow meter. The user must create a chamber to isolate the specimen of interest — this can be a window, or a bank of windows, or some other assembly. The test can isolate the window, or include the wall-window interface, depending on how the chamber is sealed to the wall.
Air leakage required to maintain a pressure difference is measured through the airflow meter. The result can be displayed as a flow (L/s or m3/hr) or a flow per unit area (L/s/m2 or m3/hr/m2, which is more common in door testing), or in the A440 units of m3/hr per metre of crack length. This can then be compared to the A rating, remembering that the field measurement will probably be higher than the lab-rated specimen.
If a small amount of smoke from a smoke pencil can be applied at the exterior, it may be possible to identify leaks, but this is usually easier to do with a blower-door test. The smoke pencil can be used to visualize the locations of leaks, which can then be addressed as needed.
Ease of operation
This parameter is a concern for elderly or physically challenged occupants. The window can be tested by applying a simple spring balance to the operating hardware.
The amount of force required to initiate motion, and to maintain motion, is measured, and must be less than the levels set in the A440 Standard. The Standard also defines where to take the measurements, depending on the window operator type. Ideally, let the occupants try the windows as a supplement to the test measurements.
Often they can give you useful feedback as to the required angle of applied force, as well as the amount of force necessary to open, close or lock the window. Note that ease of operation is usually a contrary requirement to air leakage and water leakage, both of which require the window to be tightly sealed (and therefore, usually difficult to operate). Proper selection of operating hardware can address these conflicts, but the best test occurs on the installed window.
Water leakage
Resistance to wind-driven rain is a particular concern in coastal locations, but water leakage is not welcome anywhere. Thus, installed windows should be properly evaluated in this regard.
The ASTM E1105 Standard is a field version of the E 547 test, used to determine the A440 B rating. Water is uniformly sprayed on the outside of the window at a specified rate and the window is subjected to an air-pressure difference to simulate wind pressures. The pressure is cycled in an attempt to simulate gust loading: A440 requires four cycles of five minutes with pressure “on” and one minute with pressure “off,” while the water spray is continuous throughout the test. The A440.1 User’s Guide gives test air pressures.
These pressures are maintained for the four “on” cycles, so air pressure should be continuously monitored. Before testing, the window should be preconditioned. As defined in E1105, this means opening, closing and locking the window five times, to ensure that the hardware is working and the seals are not over-tightened (which would affect the ease of operation).
The window should be observed carefully for signs of leakage. A clear chamber for testing, made of either polycarbonate or acrylic sheets, will facilitate the review. Note that there is a difference between the A440 pass-fail criteria and that of the E1105 procedure.
A440 defines water leakage as:
water penetrating the window assembly and wetting interior room surfaces;
water passing through the window into the wall below the sill;
OR
water trapped in the window assembly after the test pressure is released.
Any of these three occurrences constitutes a failure under A440. The E1105 procedure only considers the first of these to be a failure, and does not mention the other two modes of failure. It is important to define pass-fail criteria BEFORE the test begins, ideally in the project specifications.
Also, the last of these criteria is somewhat subjective: if the water is still in the assembly, but the weepholes and drainage are clearly working (so that the water will eventually drain out of the assembly), this could be considered a “Pass,” even though water in the assembly after the last oneminute “off ” cycle is, strictly speaking, considered a “Fail.”
Note that the E1105 test equipment must be calibrated, and the calibration is to be repeated every six months to make sure the water spray is constant. Reviewed by Guiseppe Strazzeri.
