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New Design Challenges for Impact Windows as ICC Ramps up U-Factors

Since 1992, when Category 5 Hurricane Andrew brought devastation to many of Florida’s southern cities, the state has been fairly aggressive in maintaining a strong building code to prevent similar damage from happening again.

As such, impacted-rated windows have been a necessity in the region for a while, along with other preparedness measures. The Tampa Bay Times noted in a piece from late last year, after Hurricane Michael hit the Florida panhandle, that “every hurricane is a learning experience,” editorializing that the building code should evolve again to account for higher wind speeds across the entire state.

Impact ratings may not be changing for the panhandle just yet—two bills to strengthen the code have so far died this year. But there have been some other developments that could be influencing window and door design in Florida soon.

I attended the recent Fenestration Manufacturers Association meeting in Florida, where there was some discussion about some upcoming updates to the International Code Council building code in 2021. The Florida Building Code is based on the I-Code, meaning changes to the I-Code will eventually impact the state.

There are some new considerations to account for wind zones in Florida, for one, but there was something else I found interesting.

For the 2021 I-Code updates, U-factors are growing stricter in Climate Zone 2, which encompasses much of Florida except for the very southern tip. Unless there are last-minute modifications, residential fenestration will be required to deliver a U-factor of 0.35.

This has some implications for window makers doing business in Florida. Aluminum windows—often incorporating laminated glass, upgraded hardware and special seals—are typically favored in the state for their impact resistance.

The traditional thinking has been that U-factor wasn’t as important as impact resistance in Florida’s climate, but that might be changing with some of the aforementioned code changes in the next few years. It will be difficult for nonthermally broken aluminum framing—often used to meet impact ratings—to meet that level of performance.

Thermal breaks aren’t radical new technology, of course, but their necessity in impact windows could bring some new complexity to the manufacturing process. And, with more complexity comes more cost.

Metal alternatives like vinyl can offer inherently superior thermal performance over aluminum; it could be worth manufacturers’ consideration in the near future. While metal is inherently trusted for its strength, today’s formulations for vinyl and other composite framing can provide good impact resistance for even the toughest codes that demand it, like Florida’s.

It goes to show that thermal efficiency requirements are becoming increasingly influential, and fenestration professionals everywhere need to be seeking out ways to deliver on those needs in an effective, economical manner. 


Eric Thompson

Eric Thompson

Eric Thompson is the national account manager for Quanex. Email him at