The “25% rule” is a Florida Building Code exception that lets owners of older homes in the wind-borne debris region replace a small share of their windows without adding opening protection. It is widely misunderstood, and in Miami-Dade and Broward it rarely changes what you can install. Here is what it actually says.
What the rule says
Florida Building Code, Existing Building, Section 707.4 provides an exception for one- and two-family homes whose original building permit was applied for before March 1, 2002, located in the wind-borne debris region. For those homes, replacement windows, sliding glass doors, glass patio doors, skylights, garage doors and exterior doors with glass installed within any 12-month period are not required to have opening protection, as long as the glazed area of the replaced components does not exceed 25 percent of the total glazed opening area of the dwelling. The replacements must still be designed for the wind pressures of an enclosed building.
The City of Cape Coral publishes the exception text in its residential window and door replacement guidelines. Your local building department applies the same code section.
What it means in plain terms
- Pre-2002 home only. Homes permitted under the Florida Building Code (March 2002 and later) do not get the exception.
- 25% of glass area, not 25% of windows. The measure is the glazed area of what you replace compared with all the glazed openings in the home. Two large sliding doors can exceed 25% on their own.
- Any 12-month period. Replacing a few windows now and a few more in eight months is counted together.
- Over 25%, opening protection is required. Either impact-rated products or approved shutters on the replaced openings.
- Pressure rating still applies. Even under the exception, the replacement must meet design pressure for your location.
Miami-Dade and Broward: the HVHZ
Miami-Dade and Broward sit in the High Velocity Hurricane Zone, which has its own product approval requirements. Replacement windows and doors there need a Miami-Dade NOA or equivalent HVHZ approval, and in practice the products available and permitted are impact-rated. If you are replacing windows in Miami, Hialeah, Doral, Fort Lauderdale or Pembroke Pines, plan on impact glass regardless of the 25% exception, and confirm with your municipality. What an NOA is.
Why most homeowners skip the exception anyway
- Non-impact replacements earn no insurance opening protection credit
- Mixing non-impact and impact windows leaves the home only partly protected and still needing shutters
- Insurers and buyers look for protection on every opening
- The price gap between non-impact and impact replacement windows is smaller than the gap in benefits
How to find out what applies to your house
- Check the year of your original building permit with your county or city
- Count the glazed area of the openings you want to replace against the whole house
- Ask your contractor to confirm the requirement with the building department before ordering. We do this on every quote.
Frequently asked questions
What is the 25% rule for windows in Florida?
An exception in Florida Building Code Existing Building 707.4: pre-March 2002 one- and two-family homes in the wind-borne debris region may replace up to 25% of their total glazed area in any 12-month period without adding opening protection, provided the replacements meet design pressure.
Does the 25% rule apply in Miami-Dade?
Miami-Dade and Broward are in the High Velocity Hurricane Zone with their own product approval rules, so replacement windows there need a Miami-Dade NOA and are impact-rated in practice. Confirm with your municipality.
Is it 25% of the number of windows?
No. It is 25% of the glazed area, so large sliding doors count heavily.
Can I replace windows a few at a time to stay under 25%?
Replacements within any 12-month period are counted together, so spreading them over months within a year does not reset the count.
Is it a good idea to use the exception?
Usually not. Non-impact replacements earn no insurance credit and leave the home partly unprotected. Most homeowners replace with impact glass and get the full benefit.