Impact Glass 101.

How impact glass works

Impact-resistant window and door systems are tested as assemblies. Laminated glazing typically uses layers of glass bonded with an interlayer. A severe impact can crack the glass, but the laminated construction is intended to help hold the broken glass together and resist creating an open breach.

That distinction matters: impact-resistant does not mean unbreakable. The goal is protection of the opening under the conditions for which the complete system is approved.

Impact windows vs. shutters

Florida's building requirements in wind-borne debris regions recognize impact-resistant glazed openings as well as approved impact-resistant coverings. That means hurricane protection can come from an approved impact opening or from a separate protective system, depending on the application.

For homeowners, one practical difference is convenience: a permanently impact-rated window or door does not require installing a separate shutter over that same protected opening before a storm, assuming the opening and installation meet the applicable requirements.

Design pressure isn't one-size-fits-all

Design pressure relates to wind pressure acting on a building component. The pressure required for an opening can vary with factors such as the building, location, height, opening location and applicable code criteria.

Product approvals can also contain limits for size, pressure, configuration and installation. A product with an impressive rating in one configuration should not automatically be assumed suitable for every opening.

Florida approvals & Miami-Dade NOAs

Florida maintains a searchable Product Approval system for building products including windows and exterior doors. Approval records can identify whether a product is impact resistant, whether it is approved for use in the High-Velocity Hurricane Zone (HVHZ), and may link to installation instructions, evaluation reports and limits of use.

A Miami-Dade County Notice of Acceptance, commonly called an NOA, is another product-acceptance document. An NOA identifies the accepted product and includes conditions and limitations; its validity and applicability should be checked for the specific project.

Important: “Florida approved,” “impact resistant” and “HVHZ approved” are related terms, but they are not interchangeable. Read the actual documentation for the exact product.

Low-E, U-factor & SHGC

Low-E glass uses a low-emissivity coating designed to affect heat transfer through the glazing. It is an energy-performance feature; it is not what makes a product impact resistant.

U-factor describes the rate of heat transfer through the window or door assembly. Lower U-factor values generally indicate greater resistance to heat flow.

SHGC, or Solar Heat Gain Coefficient, describes how much solar radiation enters through the product. A lower SHGC means less solar heat gain. For a sunny Florida home, these specifications are worth comparing alongside impact performance.

What should you compare?

When comparing impact-window or door proposals, look beyond the total price. Ask each company to clearly identify:

• Manufacturer and exact product series
• Window or door style and configuration
• Impact rating and applicable product approval or NOA
• Glass package, including Low-E options when applicable
• Approved size and design-pressure limits for the configuration
• Frame material and finish
• Installation scope and what finish work is included
• Permit responsibilities
• Product and labor warranty information
• Expected project process and payment schedule

A detailed proposal makes it easier to determine whether two quotes are actually offering comparable products and scopes.