NAFS Performance Classes: A Comprehensive Guide to Window Performance Testing


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NAFS Performance Classes: A Comprehensive Guide to Window Performance Testing

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In the world of window performance testing, the North American Fenestration Standard (NAFS) is a crucial benchmark for architects, contractors, and manufacturers. NAFS-11, the updated version of the standard, provides a comprehensive framework for evaluating the performance of windows, doors, and skylights. Understanding NAFS and its performance classes is essential for ensuring building compliance and selecting the right products for your projects.

In this guide, we will explore the key concepts and features of NAFS performance classes, debunk common misconceptions, and highlight the value of NAFS certification.

NAFS and NFRC: Bridging the Gap

Before delving into the specifics of NAFS performance classes, it’s important to understand the relationship between NAFS and the National Fenestration Rating Council (NFRC). While NAFS focuses on product performance, NFRC provides energy performance ratings for fenestration products. These two standards work in tandem to ensure that windows and doors meet both structural and energy efficiency requirements.

The Four NAFS Performance Classes

NAFS Performance Classes new

The NAFS performance classes categorize fenestration products based on their intended applications and performance levels. The four classes are:

R Class: Light Duty for Residential Buildings

The R class is designed for one- and two-family dwellings. These windows are typically used in residential settings where lighter performance requirements are sufficient. The R class provides a cost-effective option for homeowners without sacrificing quality and durability.

LC Class: Medium Duty for Low-Rise and Mid-Rise Buildings

The LC class is suitable for low-rise and mid-rise multi-family dwellings and other buildings where larger sizes and higher loading requirements are expected. LC class windows offer greater versatility and performance compared to the R class, making them a popular choice for residential and light commercial projects.

CW Class: Heavy Duty for Low-Rise and Mid-Rise Buildings

The CW class is designed for low-rise and mid-rise buildings where larger sizes, higher loading requirements, limits on deflection, and heavy use are expected. These windows are more robust and can withstand more demanding environmental conditions, making them suitable for commercial and multi-family buildings.

AW Class: Severe Duty for Mid-Rise and High-Rise Buildings

The AW class is the highest level of performance in the NAFS system. AW class windows are commonly used in mid-rise and high-rise buildings that require increased loading requirements, limits on deflection, and extreme use of fenestration products. These windows provide exceptional durability and performance, making them ideal for commercial and high-end residential projects.

NAFS Gateway Requirements: Performance Grade and Design Pressure

To determine the performance of fenestration products within each class, NAFS establishes gateway requirements that include the minimum performance grade (PG), minimum design pressure (DP), minimum structural test pressure (STP), and minimum water resistance test pressure. These requirements ensure that products meet the necessary performance standards for their intended applications.

Common Misconceptions about NAFS Performance Classes

Selecting the appropriate performance class according to the North American Fenestration Standard (NAFS) guidelines is crucial when it comes to choosing windows for a building. However, there are several common misconceptions that people often fall into when making this decision. Here is some advice on how to avoid them.

improperly chosen windows due to misconceptions about NAFS classes

1. Avoid Choosing the Class Solely Based on Building Type:

One common mistake is selecting the performance class based solely on the type of building. While certain classes may be recommended for specific building types, it is essential to consider other factors that can significantly impact the window’s performance. Factors such as window size, wind exposure, and budget should also be taken into account. Ignoring these factors can lead to improper selection and potential performance issues.

2. Avoid Arbitrary Class Selection:

Applying the performance class arbitrarily without proper analysis is a common mistake to avoid. Each performance class has specific requirements and limitations, and selecting a class without considering these factors can lead to incorrect selection. It is essential to thoroughly analyze the project’s needs, including factors such as location, climate, desired energy efficiency, and wind load requirements. This analysis will help in making an informed decision and selecting the appropriate performance class.

3. Do Not Rely Solely on Performance Grade:

Another misconception is selecting the performance class based solely on the performance grade. The performance grade indicates the level of performance a window can achieve, but it should not be the sole determining factor. It is crucial to justify the class choice based on rational criteria that take into account the specific requirements and constraints of the project. This ensures that the selected class aligns with the desired performance goals.

4. Remember NAFS Classes are for NAFS Products:

It is crucial to remember that NAFS classes are designed specifically for NAFS products and should not be applied to non-NAFS products. NAFS is a standardized testing and rating system for windows, doors, and skylights. For non-NAFS products, it is necessary to consult the appropriate manuals and guidelines specific to those products. Applying NAFS classes to non-NAFS products can lead to inaccurate performance expectations and potential safety concerns.

The Value of NAFS Certification

By choosing NAFS-certified windows and doors, architects and contractors can have confidence that they are selecting products that meet building compliance requirements. NAFS certification ensures that the products have undergone rigorous testing and meet the necessary performance standards. This certification provides peace of mind and assurance that the chosen products will perform as expected.


NAFS performance classes play a crucial role in selecting and specifying fenestration products that meet the performance requirements of different projects. Understanding the distinctions between the four classes and avoiding common misconceptions is essential for making informed decisions. By considering factors such as building type, performance grade, and specific project requirements, architects and contractors can confidently choose the right NAFS performance class and ensure the success of their projects.

For more information on NAFS and to discuss your specific project needs, contact us for a consultation and tailored solution.

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