Replacement Window Rating Explained Replacement Window Rating Explained

A replacement window rating can seem confusing, but it is important to use them if you are thinking of replacing your windows. An energy rating can help protect the environment and save you money. The window rating standard is known as the AAMA 101. Here is a quick guide to explain the ratings system and what it means. 

Who Decides the Window Ratings? 

Window Ratings are published jointly by the American Architectural Manufacturers Association (AAMA), the Window and Door Manufacturers Association (WDMA) and the Canadian Standards Association (CSA). All external windows are tested according to the North American Fenestration Standard. 

What Is Tested? 

Three things are tested to give a replacement window a rating.

  • Air leakage
  • Water Penetration Resistance
  • Structural Adequacy to Resist Applied Loads

There is a minimum performance standard for each of the three attributes. 

How Are These Tested?

Air infiltration is measured using a static pressure test. Total leakage is measured. The leakage will vary greatly dependent on the size of the window. A bigger window can have bigger cracks and leaks. However smaller windows may have greater leakage rates as the cracks will take up a greater percentage of the window.  

Water resistance is dependent on the height of the window sills and how effective the window seals are. The seals must have enough contact with the window to make a water proof barrier. For a window to pass the tests there must be no water penetration. If water is found inside the window than it will fail the test. The windows are tested by putting running a water pressure cycle against the window. 

Structural performance is tested by applying a load to the window and recording the deflection. If you can see damage after the load is applied then the window will fail the test. 

All of the tests are done in a laboratory that is an AAMA approved independent laboratory. 

What are the Performance Classes? 

There are four different performance classes. These are as follows in order of building size

  • R - 1 and 2 family residences, for instance houses.
  • LC - Low rise and mid rise multi family dwellings, for instance small apartment blocks, and also other buildings where larger sizes and and greater loads are expected.
  • CW - Low rise and mid rise buildings where larger sizes, greater loads and heavier use are expected, for instance warehouses.
  • AW - High rise and mid rise where greater loads or frequent and extreme use are expected, for instance office blocks. 

For each performance class there are minimum requirements that the windows much reach. 

Energy Ratings

Finally windows are also given an energy rating. The U-value measures the window's heat loss through radiation. All windows with insulated glass need to carry a rating of at least 0.40. The higher the U-value of the windows installed, the higher the energy efficiency of the building. 

The Solar Heat Gain Coefficient rating (SHGC) measures how well the window reduces heat gain through radiation. This rating is directly linked to the U-Rating and you should look for a similar figure when installing windows. 


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