Window Fenestration

Before we tell you about the new NFRC testing requirements, we better tell you what window fenestration is and how it relates to your window selection. The latest news in the window fenestration industry will be one of our focus topics here on the OSR Blog, so come back often to stay up-to-date.

What is Window Fenestration?

The word “Fenestration” (fen-a-stra’-shun) is a reference to the placement of windows and doors throughout a building. It is derived from the Greek word Fenestra which means window, or in the medical context, fenestra is a pore. Aha, I get it, “pore”…“window” I suppose you could say fenestra means opening.

When discussing fenestration in the context of architecture, it is a reference to the presence of openings in the building design. While the focus is on windows, it also encompasses doors, skylights, and any other opening designed to transmit light from one area to another. In our industry, we use the term “window fenestration” to narrow the topic to specifically address windows incorporated into the building design.

For builders, architects, and home owners, windows are considered a fenestration product. This is where the National Fenestration Rating Council (NFRC) comes into play. The NFRC is a nonprofit organization that has developed a standard rating system for the performance of windows. The NFRC label on windows provides performance ratings for Solar Heat Gain, Air Leakage, U-Factor, and Visible Transmittance.

New NFRC/EPA Testing Requirements for 2017

The NFRC has announced that the EPA is reducing the percentage of products that must be tested in the NFRC Independent Verification Program beginning in January of 2017. Under the current guidelines 10% of windows must be tested to achieve the ENERGY STAR® rating. Moving forward, under the new guidelines, only 5% of windows require the testing.

In an era when it seems like there are more and more restrictions, regulations, and testing; it is nice to see the early success of the NFRC labeling program. Just three years into the full implementation of the program, the EPA has such confidence in the inspection process, they are willing to reduce the sampling size by half. This speaks highly to the overall integrity of the program.

What Does this Mean for Consumers?

While the announcement of the new testing requirements won’t have a direct effect on consumers, they can be even more confident in the specifications found on the NFRC labels. You can sleep well at night knowing that you actually get what you pay for when you purchase ENERGY STAR® windows.

Contact Us:

Do you have additional questions about window fenestration and NFRC ratings? Contact, One Source Glass LLC at or give us a call at (815)-725-7033.