The 25 Percent Rule for Windows in Florida, Explained Plainly

The 25 percent rule you may have read about is a roofing rule, not a window rule. In Florida law, the 25 percent threshold applies when an existing roof built, repaired, or replaced under the 2007 Florida Building Code or a later edition has 25 percent or more repaired, replaced, or recovered. Window replacement follows a different set of conditions. This guide explains each one in plain terms.

The Short Answer: What the 25 Percent Rule Means for Windows

The 25 percent figure in Florida law applies to roofs, not windows. The Florida windstorm loss mitigation law says that if an existing roofing system was built or replaced under the 2007 Florida Building Code or a later edition, and 25 percent or more of it is being repaired, replaced or recovered, only that portion must meet the code in effect.

The rule is about proportion. It asks what share of the roof is being worked on. It does not ask how much the whole home is worth or how much the job costs.

Window work is judged differently. The Florida Building Code lists specific conditions for replacing windows and doors. Those conditions focus on size, location, wind zone and design pressure. The sections below walk through each one.

Where the Threshold Comes From: The Florida Building Code

The Florida Building Code is the statewide rulebook that local building departments use. The Florida Building Code statute says the code covers the design, construction, alteration, repair and demolition of buildings, and how those rules are enforced.

Existing buildings get their own treatment. Repairs and alterations to an older home are handled differently from brand-new construction. The 2026 Florida Building Code analysis of changes says that section points to Chapter 14 and Chapter 7 so flashing requirements are met.

You can see that exact language in the Florida Building Code supplement.

How Window Replacement Is Measured Under the Code

Under Section 107.1.1, sealed drawings by a design professional are not required for replacing windows, doors, or garage doors in an existing one-family or two-family dwelling or townhouse when the listed conditions are met (source). The exception applies when all of the following conditions are met (source):

• The new units are installed per the manufacturer’s instructions for the wind zone.
• They meet the design pressure requirements of the current Florida Building Code, Residential.
• A copy of the manufacturer’s instructions goes with the permit application, on paper or digitally.
• The new units are the same size and go in the same opening as the old ones.

Here is an illustration, not a prediction. Suppose a homeowner has 12 windows and replaces 3 of them. A larger unit, or one moved to a new opening, fails the same-size and same-opening test.

Impact Window Requirements in Wind-Borne Debris Regions

Impact windows matter most in wind-borne debris regions, which are hurricane-prone areas near the coast or in high wind zones. The 2024 Florida Building Code annual technical amendment defines the region as areas within 1 mile of the coastal mean high water line where the ultimate design wind speed (Vult) is 130 mph or greater. It also includes areas where Vult is 140 mph or greater.

State law adds a rule for larger projects. The Florida windstorm loss mitigation law says that a permitted project applied for on or after July 1, 2008, estimated at $50,000 or more, on a building in the wind-borne debris region, must include opening protections required for new construction. This applies when the building has an insured value of $750,000 or more or, if the building is uninsured or for which documentation of insured value is not presented, has a just valuation for the structure for purposes of ad valorem taxation of $750,000 or more. Roof covering replacement or repair that prevents degradation is excluded.

Impact-resistant windows are a common way to provide opening protection. Whether a specific South Florida address falls inside the region depends on the wind-borne debris region as defined in s. 1609.2 of the International Building Code (2006).

How the 25% Roofing Rule Differs From the Window Rule

The 25% roofing rule looks at how much of an existing roof is repaired, replaced or recovered. The window rule looks at the conditions of each replacement. They answer different questions, so mixing them up gives the wrong answer.

The roofing exception has another limit. The statute says the Florida Building Commission adopts this exception by rule. A local government may not adopt by ordinance an administrative or technical amendment to this exception. Roof work also needs a permit in many places. The City of Miami roofing permit page says residential and commercial roof repair or replacement requires a permit.

To sort your question, ask what part of the building is involved. If it’s the roof, the 25% roofing rule applies when an existing roofing system or roof section built, repaired, or replaced under the 2007 Florida Building Code or a later edition has 25 percent or more repaired, replaced, or recovered. Our roof replacement and roof repair services cover roof-specific questions. For windows or doors, the conditions in Section 107.1.1 apply (source).

Questions Homeowners Ask Before Deciding on Impact Windows

Impact windows help protect openings during storms. The cost depends on the size, count and specification of the project. Our team can walk you through hybrid vinyl impact windows and impact doors during your free initial consultation, which is confidential and carries no obligation to continue. The Florida Office of Insurance Regulation explains that homeowners can submit an official mitigation inspection form to an insurance agent to seek hurricane-wind mitigation premium discounts.

If you’re handling this for a family home, a rental, or a building you manage after an inspection or insurance question, you don’t have to work through it alone. Reach out through the ASP Superhome contact page, and we’ll talk through your windows, your building’s location and your question. Our free first consultation is confidential, with no obligation to continue.