You are here Home » Tech » How To's » A Straightforward Guide on How to Read an Impact Window Rating Scale

A Straightforward Guide on How to Read an Impact Window Rating Scale


Did you know that, according to the Congressional Budget Office, annual cost associated with hurricane damage now exceeds $28 billion? During these events, glass windows and doors are often the first things to go.

The threat of storm damage to your home can be anxiety-inducing. Understanding the “impact window rating scale” can be the first step to knowing whether your home is secure, and what you might do to be better prepared for storms.

Hurricanes, tornadoes, and even regular high-speed winds can cause significant damage to weaker windows. Installing impact windows can mitigate this threat, and provide peace of mind. You can know that your home is secure and that everything in it is safe.

If you are considering beefing up your windows or doors against the threat of storms, the information below will point you in the right direction. Even if you don’t live in an area prone to severe weather, there are many other benefits of impact windows, such as durability and protection against break-ins.

What Are Impact Windows?

Impact windows combine heavy-duty frames with panes of very thick, laminated glass. The panes of glass are sandwiched together with a very thin layer of polyvinyl butyral (PVB), which is a clean, durable, water-resistant plastic. In the event that the glass in the window breaks, this prevents it from shattering and falling apart.

Impact windows are constructed and installed using special silicone adhesives so that they do not pull apart during severe weather. They require specialty installation, to ensure a proper fit and so that the window function is optimized.

In addition to protecting your belongings, as well as yourself and your loved ones, these robust products can help guard against serious damage to the structure of your home. Once hurricane-force winds enter a building, the roof and walls become more susceptible. Impact windows fortify your home’s infrastructure against this breakdown.

Impact window frames can be made of metal, vinyl, or wood. Aluminum is a typical metal component for impact windows. It is very strong, lightweight, and low-maintenance. But it does have less insulating capacity than other types of frames.

Steel is stronger than aluminum but heavier. It can also be prone to rust if not maintained.

Vinyl insulates well and is the most economical option. However, it may be susceptible to cracking if you live in an area with dramatic fluctuations in temperature.

Wood is also great for insulating, and many people like its aesthetic appeal. However, it does require more maintenance in order to avoid rotting and decay.

Since impact windows and doors require a particular production method, they are available in a variety of styles and dimensions. This includes single- and double-hung windows, bay windows, French doors, and even sliding glass doors.

What Is the Impact Window Rating Scale?

Following Hurricane Andrew in 1992, which left more than $26 billion worth of destruction in its wake, many building codes were changed to reflect an increased ability to withstand hurricanes and other severe storms. These codes have been updated other times since the 1990’s, and they vary by state and region.

These ratings are based in part on the Federal Emergency Management (FEMA) recommendations for protecting windows and doors from wind, rain, hail, and projectiles during a storm. Note that oftentimes building codes pertain to new construction. If you live in an older home, it is possible that the windows and glass doors in it may be below current standards.

These standards are based on a series of tests of impact windows and doors that yield a “design pressure” (DP) rating. According to the American Architectural Manufacturers Association, DP is the load that a product is designed to withstand in its end-use application. It is how strong a window or door is expressed in strength against pounds per square foot (psf) of pressure.

Testing Impact Windows

Three areas of strength are measured to attain a DP rating: water resistance, air infiltration, and structural load. Other tests, like forced entry or direct impact, may be performed on products, but are not necessary for the DP rating calculation.

The water penetration test measures how much liquid the window keeps out per square foot of pressure. Similarly, the air infiltration test measures the amount of air it can withstand. The structural test measures the overall strength of the window, including the glass and frame.

To pass each test, the window or door must resist 1.5 times the design pressure for 10 seconds without the product suffering any permanent damage. The higher the rating, the greater amount of resistance the window or door has to these elements.

The final DP is determined by the product’s ability to pass two of the three tests. You may look for “performance grade” ratings, which are given to products that pass all three categories.

For reference, in Florida, most inland residential windows range from DP-35 to DP-50. Many coastal communities require a DP-60 or above. In other areas of the country, where storms are less prevalent, you may find DP ratings as low as 15, although this is less frequent.

How Does That Translate to Withstanding Winds?

How much wind a rated impact window can withstand depends on its size. For instance, a 20 square foot window with a DP-35 rating cand withstand 130 mph winds. A 50 square foot window of the same rating could withstand slightly stronger winds, up to 140 mph.

When you hear meteorologists talk about hurricanes, they usually mention sustained winds” and may mention “gusts.” A typical hurricane has sustained winds of 100 to 150 mph, but some storms have seen sustained winds of up more than 200 mph. A window’s DP-rated resistance to sustained winds does not mean that it can hold up to bigger gusts or impacts from projectiles.

It may be tempting to only base your prospective needs on resistance to sustained winds, but these other factors are important to consider as well. What DP rating is right for your home will be determined by where you live, what the window is exposed to, and how tall your building is.

Additional Benefits of Impact Windows

Durability in general is a big advantage of impact windows. The features that make them resistant to storm damage also makes them last longer than regular windows. So, even if they are never needed during a storm, there is still a benefit to their value.

Also, impact windows provide greater protection against intruders. DP-50 ratings and above are very difficult to break. And, as stated before, even if the impact window is broken, it does not shatter–it remains in one piece.

Added protection against all of these threats can even help you lower your home insurance rates. Some policies may discount more than 40 percent off the wind mitigation portion of your premium. In storm-prone areas, this can amount to more than a quarter of your entire payment.

Impact windows contribute to great energy efficiency. Most have the option of an added pane of glass that is secured to the laminate layer, with a hermetically sealed air space in between. This can provide superior insulation and help lower energy costs.

Impact windows also can provide up to 99 percent protection against UV rays. This could be a great benefit for windows in rooms where people regularly sit or stand, such as a living room or above the kitchen sink.

Finally, due to their greater thickness, impact windows can reduce noise inside the home.

Hire a Professional

If you are handy with home projects, you may be tempted to tackle impact window installation yourself. Think twice about this. The installation processes are very complicated and require special knowledge and training.

There are a number of other reasons to hire a professional for the project. A prominent impact window installer can go over the details and help determine what product is right for your home. You may need different levels of protection depending on where the window or door is located.

Most prominent contractors will offer a warranty for their impact windows or doors. This is a good indication that they stand by their product.

Be certain to select a contractor that has a lot of experience installing impact windows. Proper licensing and training of installers may be as important as the product itself. You’ll want to have the confidence that your window or door is installed correctly, and will hold up to whatever storms throw its way.

Be Prepared

With the information above about the impact window rating scale and the many options available, you are ready to upgrade your home and ensure that it can stand up to severe weather threats.

Also, be sure to check out other posts on the intersection of technology with the many different aspects of our lives.

You may also like