So, if you’ve looked up the Florida Building Code (FBC) rules for replacing your windows in a wind borne debris region, you might have seen something like “Florida 25 window rule” and wondered: “What does this mean?”
Homeowners living in one of Florida’s designated wind borne debris regions need to have their homes built to withstand a set level of wind pressure (and the objects that 140+ mph winds can pick up and throw). Florida’s 25% window rule is an exception for homeowners living in wind borne debris (WBD) regions.
What Is the “Florida 25 Window Rule” for Wind Borne Debris Regions?
One of the requirements for homes in WBD zones is that the windows in the home need to be impact-rated so they can withstand hurricane-force winds and flying objects during one of the all-too-frequent storms that hit the panhandle during hurricane season.
The 25% window rule is an exception to the impact glass requirement.
The text of the exception is as follows:
“The replacement of garage doors and exterior doors with glazing, sliding glass doors, glass patio doors, skylights, and operable and inoperable windows within any 12-month period shall not be required to have opening protection but shall be designed for wind pressures for enclosed buildings, provided the aggregate area of the glazing in the replaced components does not exceed 25 percent of the aggregate area of the glazed openings in the dwelling or dwelling unit.”
–FBC-EB, Section 706.4, Exception 1
To translate the code from legalese to plainer speak, it means that, as long as you’re only replacing 25% or less of the total surface area of your glass windows or doors in your home, the new glass doesn’t have to be impact-rated. It only needs to meet the requirements for an interior window or door.
So, say you have 100 square feet of glass windows on your home. In a single 12-month period, you could replace up to 25 square feet of those windows with non-impact windows and still fall under the exception.
Could I Replace 25% of My Windows in December and Another 25% in January?
No. The Florida 25 window rule isn’t based on calendar years, it’s based on a 12-month period. So, if you installed new windows on December 11th, 2025, you’d have to wait until at least December 12, 2026 before doing the next set of window replacements.
If you replace any of your windows for any reason in that time, the exception no longer applies and you’ll have to remove the newly-installed non-impact windows and replace them with impact windows to avoid noncompliance with the FBC’s rules for existing buildings.
Officials enforce this rule through permits. Every new window replacement/installation job requires the submission of a permit, and officials track the cumulative area that’s replaced within a 12-month period.
If they see that the total rate of replacement exceeds 25% in a year, then you may be hit with penalties such as being forced to switch to impact windows or paying a fine.
Can I Replace 25% of My Windows with Non-Impact and Do Impact Glass for the Rest?
No. You cannot “mix and match” to exceed the 25% total glass replacement rate restriction. The exemption only applies if you’re replacing less than 25% of all your home’s exterior glass within the same 12 months.
It doesn’t matter what kind of glass you’re installing—as soon as you exceed 25% within the same 12-month period, then you no longer qualify for the exception. So, if you do 20% non-impact and 6% impact, you’ll be in violation of the FBC rules and you’ll have to switch to all impact windows.
If you do up to the 25% threshold, but then have to replace another window because it broke during a storm, accident, or intrusion attempt, then you’ll be in violation of the rules.
My House Has 12 Windows. Does That Mean I Can Replace ANY Three of Them?
Not necessarily. The rule doesn’t count windows by number, but rather by the total surface area of the glass you’re replacing. So, if you have a dozen windows, but they aren’t all the same size, you might not be able to replace any four of your windows and know that you’re following the 25% replacement rule.
For example, many homes have larger windows facing the street. Often two or three times the size of other windows in the home. So, replacing that window would count for much more of the 25% of total glass area than the other windows would.
If you’re dealing with a contractor who’s offering to replace a quarter of your windows and claiming that you’ll be fine with Code Enforcement authorities even without actually measuring your windows… run. Do not let that contractor handle your window replacement. It will only end badly.
What If One of My Other Windows Breaks and I Have to Replace It?
Say you’ve been working on replacing your windows with non-impact windows for a few years now. Just waiting a year and a day on the dot before replacing the next set of windows.
Then, right after replacing your second set of windows to make 50% of your home’s windows are non-impact glass, a baseball comes flying through your front window, shattering it and even bending the cheap aluminum frame a little because the neighbor’s kid is the second coming of Babe Ruth.
So, you now need to completely replace that window… and all of the windows you just finished installing, because you’re now above the 25% total surface area replacement limit. It doesn’t matter that the broken window was non-impact glass already, you now are replacing more than 25% of your windows within the same 12-month period, so all of your recently-installed windows need to be switched over to impact glass.
Why You Shouldn’t Rely on the 25% Rule in Wind Born Debris Regions
The biggest reason why most homeowners want to use non-impact windows is because they’re going to be less expensive than impact glass windows… at least at the time of installation. But if you’re talking to a window installation company who’s making the claim that “you don’t have to use impact windows if you’re following the Florida 25 window rule” and that you can save some money by leveraging it, we have a few rebuttals:
- Non-Impact Windows Have a Shorter Useful Life. Non-impact windows aren’t as durable or long-lasting as impact-rated windows. They may break more easily from everyday events like the “baseball through the window” example mentioned earlier. Also, ‘discount’ window brands installed because of their low cost tend to have a shorter useful life overall, even in the absence of impacts.
- Cheap Non-Impact Windows May Be Less Energy Efficient. Non-impact windows may lack some of the features that help make impact windows more energy efficient—such as having multiple layers of glass, protective laminate, and argon gas fills that prevent heat transfer between your home and the outdoors.
- Non-Impact Windows Aren’t Hurricane Resistant. In a storm, a non-impact window is more likely to break, requiring you to repair or replace the window. This means spending more money on fixing a problem that would not have been as likely to happen with a hurricane impact window.
- Broken Windows Can Result in Damage to the Home. When a window breaks during a storm, the window may not be the only thing to get damaged. A broken window becomes an ingress point for wind, water, insects, debris, and more into your home. That can mean spending more money replacing damaged flooring, furniture, interior walls, electrical wiring, etc. In a worst-case scenario during a major hurricane, the broken window may even allow the wind to destroy the home as it pushes on internal walls as well as the exterior walls.
- Hurricane Impact Windows Protect the Home Even if They Crack. Impact windows built for high-velocity hurricane zones (HVHZs) include a layer of flexible laminate behind the top layer of glass. This laminate layer flexes when the top layer of glass breaks following an impact, absorbing the shock and maintaining the barrier between your home and the outside. With this layer, your home is protected even if the top layer of glass breaks. Additional layers of glass may also help protect your home, though the number of glass layers varies depending on the window’s manufacturer.
The price difference between non-impact windows and impact windows doesn’t justify the risk of damage to the home or having to replace the windows again as soon as the next big storm hits.
So, we recommend to our customers living in Florida’s wind-borne debris regions to use impact windows rather than relying on the 25% rule. It can actually save you money in the long run and reduces potential headaches down the line.
If you’re looking for a reliable window replacement service that will help you save money in the long run, Karoly Windows & Doors is here to help. We don’t cut corners on our installation jobs. We use 100% in-house technicians who are certified for window installation work in Florida. We partner with top-tier Floridian window manufacturers to provide top-tier windows. And we back it all up with a Platinum Standard Lifetime Guarantee that we can maintain precisely because of our total commitment to providing best-in-class service.
