WDMA Clarifies Rating System in Current Standard

The Window and Door Manufacturers Association (WDMA) has issued a press release recently to clarify the rating system in 101/I.S. 2/NAFS-02, Voluntary Specification for Windows, Skylights and Glass Doors developed jointly by the WDMA and the American Architectural Manufacturers Association (AAMA).

The current code referenced performance standard for single and dual action windows, skylights and glass doors used in new construction and replacement applications.

Within its nine sections, section four, general requirements, covers the rating system and test size guidelines, which are described further below.

Gateway Performance Requirements

For each product type, there is a set of primary (or preliminary) minimum allowable performance levels referred to as "gateway" or "passport" requirements that a test specimen must meet in order for it to be rated. These performance levels are for air leakage resistance, water penetration resistance, uniform load and forced-entry resistance. The size of the test specimens must be equal to or larger than the specified minimum size (in both height and width). Once the minimum test requirements have been met, the product can be rated within one of these five performance classes:

• Residential (R);
  
• Light construction (LC);
  
• Commercial (C);
  
• Heavy construction (HC); and
  
• Architectural (A).

Product Designations

A four-part designation or code identifies the rating the window or door product has achieved. It consists of the product type, performance class, performance grade and maximum size tested. Twenty-six product types are identified by a letter code. For example, "H" is the code for single, double or triple hung windows; "HGD" is used for hinged glass doors; and "VS" designates vertical sliding windows.

Performance Class is designated by the one- or two-letter code previously discussed. Performance Grade is based on design pressure (DP) or the windload resistance a window or door is designed to withstand when closed and locked. A higher number equates to higher performance. DP is measured in either pounds per square foot (psf) or Pascals (Pa), and is based on a structural test of the product at 1.5 times the design pressure or DP rating. A rating of DP 40, for instance, indicates that the product was tested to 60 pounds per square foot and withstood water penetration under conditions equal to 15 percent of the design pressure. Each performance class has a minimum DP performance requirement. These are: Residential: 15 psi (720 Pa) Light Construction: 25 psi (1200 Pa) Commercial: 30 psi (1440 Pa) Heavy Construction: 40 psi (1920 Pa) Architectural: 40 psi (1920 Pa).

The maximum test size, a critical factor in determining compliance with the standard, is designated as the test unit width times height, in millimeters, for example 705 x 1503. Actual labeled products must be the same size or smaller than this size in order for the rating to be valid.

A typical product designation for a dual horizontal sliding window would be:

HS-DW-LC 25 1800 X 1400 (71 X 55)
HS (horizontal sliding window)-DW (dual window) LC (light commercial) 25 (DP) 1800 x 1400 (size tested)

Roof windows and skylights, however, will be designated by a five-part code. In this case, there will be two performance grades: positive design pressure (long duration) and negative design pressure (short duration). A typical product designation would be:

SKG-R 30 20 1200 X 1200 (47 X 47)
SKG (skylights/glass glazed) R (residential) 30 (DP-long duration) 20 ( DP -short duration) 1200 x 1200 (size tested).

Products can be tested to Optional Performance Grades (DP) which are higher than the minimum performance grade. Optional Performance Grades require additional tests for products, including higher uniform load structural test pressures and higher water resistance test pressures to provide higher DP ratings for special conditions related to weather and climate, height of the installation or the type of the structure.

The next edition of the standard, AAMA/CSA/WDMA 101/I.S.2/A440, Specifications for Windows, Doors and Unit Skylights, has already been approved by both AAMA and WDMA, and is currently undergoing public review and approval by the Canadian Standards Association (CSA). The rating system in the new standard is the same as the current 101/I.S.2/NAFS-02. AAMA and WDMA are co-sponsoring submittals to the International Code Council to upgrade references in the 2006 editions of the International Building Code (IBC) and International Residential Code (IRC) to the new standard. Petitions will also be made to the National Building Code of Canada (NBC) to update its references to the new standard.

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