Window ratings set the expected performance. Understanding the system will allow you to select appropriate ratings for project requirements.

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Providing:
Specifications, Quality Assurance, THE MEANING OF WINDOW RATINGS
Inspections & Investigations
for your Construction Projects By David Stutzman, AIA, CSI, CCS, SCIP, LEED AP
ABSTRACT: Primary Standard
Window ratings set the expected Exterior windows are often tested  CW - Low-rise and mid-rise
performance. Understanding the and rated according to the North buildings where larger sizes,
system will allow you to select American Fenestration Standard greater loads, and heavy use are
appropriate ratings for project expected.
published jointly by the American
requirements.
Architectural Manufacturers  AW - High-rise and mid-rise
buildings where greater loads or
Association (AAMA), the Window &
FILING: frequent and extreme use are
Door Manufacturers Association expected.
UniFormat™ (WDMA), and the Canadian For each performance class, AAMA
B2020 - Exterior Windows Standards Association (CSA). For 101 sets minimum gateway
purposes of this article, the requirements that the windows
MasterFormat™ standard will be referenced as must meet. The gateway
08 50 00 - Windows AAMA 101. This reference requirements include a minimum
standard sets minimum window size for testing purposes.
performance for three primary The minimum sizes vary
KEYWORDS: depending on performance class
attributes to establish an overall
Window, performance class, and the type of window.
performance grade, air infiltration, performance grade:
water penetration, structural Window design pressures are
 Air leakage
performance determined by the building code.
 Water penetration resistance The pressure is calculated from
 Structural adequacy to resist the wind speed, wind exposure
REFERENCES: applied loads factor, wind importance factor,
AAMA/WDMA/CSA
AAMA 101 sets four basic height above grade, and location
101/I.S.2/A440 - North American on the façade. Consult the project
performance classes based on
Fenestration
common use for the type of facility structural engineer to determine
Standard/Specification for
windows, doors, and skylights. (height of window above grade), actual project wind loads.
ASTM E283 - Standard Test expected wind loads, and For windows to be labeled as
Method for Determining Rate of expected use. These are listed in AAMA 101 compliant, the windows
Air Leakage Through Exterior ascending order from least to must be tested by an AAMA
Windows, Curtain Walls, and Doors greatest performance. approved independent laboratory.
Under Specified Pressure Labeled windows are listed in the
Differences Across the Specimen  R - One- and two-family dwellings searchable Certified Products
ASTM E330 - Standard Test  LC - Low-rise and mid-rise multi- Directory on the AAMA website.
Method for Structural Performance family dwellings and other
of Exterior Windows, Doors, buildings where larger sizes and
Skylights and Curtain Walls by greater loads are expected.
Uniform Static Air Pressure
Difference
ASTM E331 - Standard Test AAMA 101 Minimum Gateway Performance
Method for Water Penetration of
Performance Minimum Minimum Min. Test Pressures
Exterior Windows, Skylights, Class Performance Design (psf)
Doors, and Curtain Walls by Grade Pressure (psf)
Uniform Static Air Pressure Structural Water
Difference R 15 15.0 22.5 2.90
ASTM E547 - Standard Test LC 25 25.0 37.5 3.75
Method for Water Penetration of
Exterior Windows, Skylights, CW 30 30.0 45.0 4.50
Doors, and Curtain Walls by Cyclic AW 40 40.0 60.0 8.00
Static Air Pressure Difference

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Air Infiltration ASTM E331 with a uniform static with ASTM E330 Procedure A.
Air infiltration is measured by pressure. Observable permanent damage
ASTM E283. This is a static from the test is cause for failure.
Water resistance is dependent on
pressure test that measures total Permanent deflection of framing
the sill height and effective seals.
leakage through the entire window and sash members exceeding the
A sill 0.56 inches high will resist
assembly. Because the leakage is allowable percentage of span also
water penetration with a 2.90 psf
dependent on the size and length constitutes failure. Allowable
differential pressure, without
of cracks, the actual window size deflections are 0.4% for R and LC,
seals. Seals must remain in
can dramatically affect the leakage 0.3% for CW, and 0.2% for AW.
sufficient contact with the window
rate that is reported in cfm/sq ft.
Windows smaller than the gateway
sash under positive pressure to Conclusion:
maintain an effective water barrier.
size will likely have greater Inward opening windows rely on When selecting windows by AAMA
leakage rates because the cracks the window hardware to maintain 101 performance class and
will be greater as a percentage of the water seal. performance grade, ensure that
the window opening. the minimum gateway size is
To pass the test, there must be no greater than the size required for
AAMA 101 sets the test pressure water penetration as defined by the project. Oversized windows
and allowable leakage by the ASTM tests. This means that may require additional testing to
performance class and seal type. no water may be observed beyond confirm the window will perform.
Most windows will have air leakage a plane parallel to the glazing and
rates that are less than the intersecting the innermost Specifying a performance grade
maximum allowed by AAMA 101. projection of the test specimen, will set the window design
excluding hardware and trim. This pressure. Be sure to consider the
Performance Test Max. Air
definition permits water to collect increased loads at the building
Class Pressure Leakage
(psf) (cfm/sf) in the sill and then weep to the upper floors and corners.
R (jalousie only) 1.6 1.2 exterior when the test ends. AAMA 101 performance classes
R, LC, CW 16. 0.3 and performance grades can be
(except Jalousie) helpful for specifying windows.
AW (sliding 6.2 0.3 Specific project criteria for design
seal) loads and air infiltration must be
AW 62. 0.1 specified to ensure the correct
(compression performance is attained.
seal & fixed)
Air leakage will impact the HVAC
system. Uncontrolled air
infiltration requires additional Add Your Comments
Water penetration observed on the
capacity to maintain the building We invite your comments. Visit our
interior window stool or jamb
interior environmental design blog and add your comments to this
returns would be cause for failure.
conditions. article's announcement.
www.conspectusinc.com/blog
Structural
Water Penetration Performance The information contained in this
document is offered for educational
The test used to determine water Structural performance is purposes, only, and not as technical
penetration resistance is ASTM measured by applying a uniform advice suitable for any particular
E547. This test alternates between positive and negative load to the project or specific condition. Technical
a pressure cycle and a non- window and recording the consulting is unique to the facts of a
pressure cycle. The pressure is particular condition, and Conspectus
deflection. The test pressure is
applied to the window exterior. recommends that a specialist be
150% of the design pressure. The
AW windows are also tested to consulted to determine solutions for
test is conducted in accordance
each specific condition.