Impact ratings on doors and windows seem impressive, but many homeowners don’t understand what they mean. The labels and certifications are full of technical jargon and refer to tests that aren’t very visual. Yet these ratings help determine whether or not the door and window protects the home from the hurricane or fail as the point of least resistance and cause catastrophic destruction.
By knowing what these ratings truly mean, homeowners can make better decisions in choosing products for hurricane protection. Not all impact-resistant doors and windows perform the same, and when wind speeds reach triple digits and debris swirls about, the differences, however subtle, matter.
What do impact ratings truly test?
Impact-resistant doors and windows undergo standardized testing to simulate conditions in a hurricane. The first test is a large missile – testing provides different scenarios from small missiles or different object sizes.
They take a nine-pound 2×4 and shoot it at the glass at 34 miles per hour (that’s a large missile) or small projectiles (for different scenarios). This represents the kind of debris that a hurricane provides – when the wind picks up something heavy – a roof tile, a tree branch, a piece of a neighboring wall – and tosses it through the air at your home. The idea is that the glass should shatter but not penetrate and let the board through.
Next, the window/door undergoes cyclic pressure testing – the type of pressure created by extreme positive pressure and negative pressure (remember-hurricanes blow in and suck out). The push pull of a hurricane can extremely devalue a window/door as it sucks/pushes it out/in of its frame.
The two types of impact protection
There are two kinds of impact protection that provide different levels of success in the real world.
Laminated glass consists of two panes of glass with a plastic film interlayer separating them. When something hits laminated glass, the exterior glass may shatter, but the interlayer prevents penetration while the pieces stay in place. Think of your car windshield. It cracks upon impact but doesn’t cave in. The other option is to use impact-resistant film to regular tempered glass; this is less common and reliable, however, as the quality of adhesion varies, and its integrity diminishes over time (especially in hot, humid conditions).
In hurricane-prone areas, however, if laminated glass remains an option, energy efficient doors in Florida with such laminated glass are energy-efficient doors as well since they provide hurricane protection and insulation.
Design pressure ratings
Design pressure (DP) ratings indicate how much wind pressure doors and windows can hold. A DP50 means that whatever rating (pounds per square foot) it stands for (for example, 50 pounds per square foot) is what this window can withstand. For reference, 140 mph winds (Category 4 hurricane) equal about 100 pounds per square foot.
Every DP rating includes positive AND negative pressure – wind pushes on the outside and sucks/pulls from the inside (in fact, windows usually fail more often on the negative side than homeowners realize – hurricanes aren’t in-funnel only; they suck air out quicker than people realize).
The higher the DP rating, the more it can withstand stronger storms and higher costs. Ask your code office what building code is required.
Large missile/small missile ratings
There are two categories of missiles that are tested when glass is impacted – and pricing differs based on protection levels.
Large missile impact testing is that nine-pound 2×4 as discussed. This represents debris that is substantial – a piece of lumber or a major branch. Those products pass large missile testing mean they have extreme levels of impact protection.
Small missile testing uses steel balls that weigh two grams shot at glass at varying distances. This is gravel or small stones. Small missile-rated products cost less but also protect less against large missiles.
Hurricane codes usually call for large missile impact resistance; less risky hurricane zones call for small missile ratings to be acceptable.
Importance of installation in impact rated performance
The most highly rated impact rated door or window fails if it’s improperly installed.
The framing needs to be correctly secured to the frame structure. Where there’s a seal between frame/wall, it shouldn’t allow water penetration under pressure. Fasteners need to be proper for type, spacing, and depth to ensure no weak points exist. In a hurricane, any weak point during installation signifies failure.
In a lab where testing occurs, things are mounted perfectly. In reality, however, not everything gets installed perfectly which means certified installers who understand impact performance needs matter more than some homeowners realize.
Hurricane codes/testing standards
Building codes in hurricane-prone areas determine minimum impact/pressure ratings based on wind zone maps/exposure categories from FEMA/DHS. These are not suggestions but mandates for new construction generally and replacement windows/doors as well.
There are different testing standards; products could get certified through more than one company but some jurisdictions require more stringent assets that act as standards throughout coastal regions. Building codes apply minimum requirements; ASTM International tests all products nationwide.
A product might get passed through one standard but not another, or meet requirements from certain wind zones but not all. Understand exactly what the certification says.
What ratings fail to tell you
What impact ratings don’t tell you are just as important as what they do.
Corrosive resistance happens in salt air with marine qualities but isn’t tested for impact factors – therefore a door/window could potentially do great under impact resistance but better in a non-marine environment if its hardware fails after one season in such conditions.
Water infiltration might occur after conditions exceeding what’s tested for even if there’s impact access success; real hurricanes provide hours of water-driven rain at pressures more successful at getting through than what’s tested for.
Energy efficiency matters when homeowners want both but there are separate categories for that. A door/window might have excellent protection during hurricanes but poor insulating value or vice versa; both need checking separately for other relevant properties.
How to make sense of labeling
Homeowners looking for impact resistant products should make sense of their testing ratings – and labels matter most.
For windows/doors they should find:
- The impact rating (large/small missile)
- The design pressure rating
- Which testing standards were met
- Is it rated for complete assembly/glass (sometimes frames aren’t rated up to par with glazing)
- Is it rated for this specific wind zone? Is it rated for local code? What may be good enough for inland areas might NOT pass muster for high velocity hurricane zone coastal needs.
Impact ratings aren’t something that’s technical specification fluff just beyond pricing and aesthetic choice; they determine if your home’s envelope can withstand hurricane-strength winds and flying debris. Knowing how to assess what they truly mean helps homeowners better purchase options for verification of local requirements.